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d5f930fe76
std: improve documentation for get_mut() methods regarding forgotten guards Fixes #139034 This PR improves the documentation for `get_mut()` methods in `Mutex`, `RefCell`, and `RwLock` to clarify their behavior when lock guards are forgotten (e.g., via std::mem::forget). The current documentation for these methods states that a mutable borrow "statically guarantees no locks exist", which is not entirely accurate. While a mutable borrow prevents new locks from being created, it does not clear or detect previously abandoned locks through `forget()`. This can lead to counterintuitive behavior: https://play.rust-lang.org/?version=stable&mode=debug&edition=2024&gist=e68cefec12dcd435daf2237c16824ed3 https://play.rust-lang.org/?version=nightly&mode=debug&edition=2024&gist=81263ad652c752afd63c903113d3082c https://play.rust-lang.org/?version=stable&mode=debug&edition=2024&gist=311baa4edb3abf82a25c8d7bf21a4a52 r? libs
2486 lines
86 KiB
Rust
2486 lines
86 KiB
Rust
//! Shareable mutable containers.
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//!
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//! Rust memory safety is based on this rule: Given an object `T`, it is only possible to
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//! have one of the following:
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//!
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//! - Several immutable references (`&T`) to the object (also known as **aliasing**).
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//! - One mutable reference (`&mut T`) to the object (also known as **mutability**).
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//!
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//! This is enforced by the Rust compiler. However, there are situations where this rule is not
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//! flexible enough. Sometimes it is required to have multiple references to an object and yet
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//! mutate it.
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//!
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//! Shareable mutable containers exist to permit mutability in a controlled manner, even in the
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//! presence of aliasing. [`Cell<T>`], [`RefCell<T>`], and [`OnceCell<T>`] allow doing this in
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//! a single-threaded way—they do not implement [`Sync`]. (If you need to do aliasing and
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//! mutation among multiple threads, [`Mutex<T>`], [`RwLock<T>`], [`OnceLock<T>`] or [`atomic`]
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//! types are the correct data structures to do so).
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//!
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//! Values of the `Cell<T>`, `RefCell<T>`, and `OnceCell<T>` types may be mutated through shared
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//! references (i.e. the common `&T` type), whereas most Rust types can only be mutated through
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//! unique (`&mut T`) references. We say these cell types provide 'interior mutability'
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//! (mutable via `&T`), in contrast with typical Rust types that exhibit 'inherited mutability'
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//! (mutable only via `&mut T`).
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//!
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//! Cell types come in four flavors: `Cell<T>`, `RefCell<T>`, `OnceCell<T>`, and `LazyCell<T>`.
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//! Each provides a different way of providing safe interior mutability.
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//!
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//! ## `Cell<T>`
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//!
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//! [`Cell<T>`] implements interior mutability by moving values in and out of the cell. That is, an
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//! `&mut T` to the inner value can never be obtained, and the value itself cannot be directly
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//! obtained without replacing it with something else. Both of these rules ensure that there is
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//! never more than one reference pointing to the inner value. This type provides the following
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//! methods:
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//!
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//! - For types that implement [`Copy`], the [`get`](Cell::get) method retrieves the current
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//! interior value by duplicating it.
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//! - For types that implement [`Default`], the [`take`](Cell::take) method replaces the current
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//! interior value with [`Default::default()`] and returns the replaced value.
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//! - All types have:
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//! - [`replace`](Cell::replace): replaces the current interior value and returns the replaced
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//! value.
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//! - [`into_inner`](Cell::into_inner): this method consumes the `Cell<T>` and returns the
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//! interior value.
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//! - [`set`](Cell::set): this method replaces the interior value, dropping the replaced value.
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//!
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//! `Cell<T>` is typically used for more simple types where copying or moving values isn't too
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//! resource intensive (e.g. numbers), and should usually be preferred over other cell types when
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//! possible. For larger and non-copy types, `RefCell` provides some advantages.
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//!
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//! ## `RefCell<T>`
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//!
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//! [`RefCell<T>`] uses Rust's lifetimes to implement "dynamic borrowing", a process whereby one can
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//! claim temporary, exclusive, mutable access to the inner value. Borrows for `RefCell<T>`s are
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//! tracked at _runtime_, unlike Rust's native reference types which are entirely tracked
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//! statically, at compile time.
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//!
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//! An immutable reference to a `RefCell`'s inner value (`&T`) can be obtained with
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//! [`borrow`](`RefCell::borrow`), and a mutable borrow (`&mut T`) can be obtained with
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//! [`borrow_mut`](`RefCell::borrow_mut`). When these functions are called, they first verify that
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//! Rust's borrow rules will be satisfied: any number of immutable borrows are allowed or a
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//! single mutable borrow is allowed, but never both. If a borrow is attempted that would violate
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//! these rules, the thread will panic.
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//!
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//! The corresponding [`Sync`] version of `RefCell<T>` is [`RwLock<T>`].
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//!
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//! ## `OnceCell<T>`
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//!
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//! [`OnceCell<T>`] is somewhat of a hybrid of `Cell` and `RefCell` that works for values that
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//! typically only need to be set once. This means that a reference `&T` can be obtained without
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//! moving or copying the inner value (unlike `Cell`) but also without runtime checks (unlike
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//! `RefCell`). However, its value can also not be updated once set unless you have a mutable
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//! reference to the `OnceCell`.
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//!
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//! `OnceCell` provides the following methods:
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//!
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//! - [`get`](OnceCell::get): obtain a reference to the inner value
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//! - [`set`](OnceCell::set): set the inner value if it is unset (returns a `Result`)
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//! - [`get_or_init`](OnceCell::get_or_init): return the inner value, initializing it if needed
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//! - [`get_mut`](OnceCell::get_mut): provide a mutable reference to the inner value, only available
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//! if you have a mutable reference to the cell itself.
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//!
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//! The corresponding [`Sync`] version of `OnceCell<T>` is [`OnceLock<T>`].
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//!
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//! ## `LazyCell<T, F>`
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//!
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//! A common pattern with OnceCell is, for a given OnceCell, to use the same function on every
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//! call to [`OnceCell::get_or_init`] with that cell. This is what is offered by [`LazyCell`],
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//! which pairs cells of `T` with functions of `F`, and always calls `F` before it yields `&T`.
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//! This happens implicitly by simply attempting to dereference the LazyCell to get its contents,
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//! so its use is much more transparent with a place which has been initialized by a constant.
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//!
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//! More complicated patterns that don't fit this description can be built on `OnceCell<T>` instead.
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//!
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//! `LazyCell` works by providing an implementation of `impl Deref` that calls the function,
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//! so you can just use it by dereference (e.g. `*lazy_cell` or `lazy_cell.deref()`).
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//!
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//! The corresponding [`Sync`] version of `LazyCell<T, F>` is [`LazyLock<T, F>`].
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//!
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//! # When to choose interior mutability
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//!
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//! The more common inherited mutability, where one must have unique access to mutate a value, is
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//! one of the key language elements that enables Rust to reason strongly about pointer aliasing,
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//! statically preventing crash bugs. Because of that, inherited mutability is preferred, and
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//! interior mutability is something of a last resort. Since cell types enable mutation where it
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//! would otherwise be disallowed though, there are occasions when interior mutability might be
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//! appropriate, or even *must* be used, e.g.
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//!
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//! * Introducing mutability 'inside' of something immutable
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//! * Implementation details of logically-immutable methods.
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//! * Mutating implementations of [`Clone`].
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//!
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//! ## Introducing mutability 'inside' of something immutable
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//!
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//! Many shared smart pointer types, including [`Rc<T>`] and [`Arc<T>`], provide containers that can
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//! be cloned and shared between multiple parties. Because the contained values may be
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//! multiply-aliased, they can only be borrowed with `&`, not `&mut`. Without cells it would be
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//! impossible to mutate data inside of these smart pointers at all.
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//!
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//! It's very common then to put a `RefCell<T>` inside shared pointer types to reintroduce
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//! mutability:
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//!
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//! ```
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//! use std::cell::{RefCell, RefMut};
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//! use std::collections::HashMap;
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//! use std::rc::Rc;
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//!
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//! fn main() {
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//! let shared_map: Rc<RefCell<_>> = Rc::new(RefCell::new(HashMap::new()));
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//! // Create a new block to limit the scope of the dynamic borrow
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//! {
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//! let mut map: RefMut<'_, _> = shared_map.borrow_mut();
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//! map.insert("africa", 92388);
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//! map.insert("kyoto", 11837);
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//! map.insert("piccadilly", 11826);
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//! map.insert("marbles", 38);
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//! }
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//!
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//! // Note that if we had not let the previous borrow of the cache fall out
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//! // of scope then the subsequent borrow would cause a dynamic thread panic.
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//! // This is the major hazard of using `RefCell`.
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//! let total: i32 = shared_map.borrow().values().sum();
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//! println!("{total}");
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//! }
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//! ```
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//!
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//! Note that this example uses `Rc<T>` and not `Arc<T>`. `RefCell<T>`s are for single-threaded
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//! scenarios. Consider using [`RwLock<T>`] or [`Mutex<T>`] if you need shared mutability in a
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//! multi-threaded situation.
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//!
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//! ## Implementation details of logically-immutable methods
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//!
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//! Occasionally it may be desirable not to expose in an API that there is mutation happening
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//! "under the hood". This may be because logically the operation is immutable, but e.g., caching
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//! forces the implementation to perform mutation; or because you must employ mutation to implement
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//! a trait method that was originally defined to take `&self`.
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//!
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//! ```
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//! # #![allow(dead_code)]
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//! use std::cell::OnceCell;
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//!
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//! struct Graph {
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//! edges: Vec<(i32, i32)>,
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//! span_tree_cache: OnceCell<Vec<(i32, i32)>>
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//! }
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//!
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//! impl Graph {
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//! fn minimum_spanning_tree(&self) -> Vec<(i32, i32)> {
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//! self.span_tree_cache
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//! .get_or_init(|| self.calc_span_tree())
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//! .clone()
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//! }
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//!
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//! fn calc_span_tree(&self) -> Vec<(i32, i32)> {
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//! // Expensive computation goes here
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//! vec![]
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//! }
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//! }
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//! ```
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//!
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//! ## Mutating implementations of `Clone`
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//!
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//! This is simply a special - but common - case of the previous: hiding mutability for operations
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//! that appear to be immutable. The [`clone`](Clone::clone) method is expected to not change the
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//! source value, and is declared to take `&self`, not `&mut self`. Therefore, any mutation that
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//! happens in the `clone` method must use cell types. For example, [`Rc<T>`] maintains its
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//! reference counts within a `Cell<T>`.
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//!
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//! ```
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//! use std::cell::Cell;
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//! use std::ptr::NonNull;
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//! use std::process::abort;
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//! use std::marker::PhantomData;
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//!
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//! struct Rc<T: ?Sized> {
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//! ptr: NonNull<RcInner<T>>,
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//! phantom: PhantomData<RcInner<T>>,
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//! }
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//!
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//! struct RcInner<T: ?Sized> {
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//! strong: Cell<usize>,
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//! refcount: Cell<usize>,
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//! value: T,
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//! }
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//!
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//! impl<T: ?Sized> Clone for Rc<T> {
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//! fn clone(&self) -> Rc<T> {
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//! self.inc_strong();
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//! Rc {
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//! ptr: self.ptr,
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//! phantom: PhantomData,
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//! }
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//! }
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//! }
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//!
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//! trait RcInnerPtr<T: ?Sized> {
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//!
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//! fn inner(&self) -> &RcInner<T>;
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//!
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//! fn strong(&self) -> usize {
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//! self.inner().strong.get()
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//! }
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//!
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//! fn inc_strong(&self) {
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//! self.inner()
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//! .strong
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//! .set(self.strong()
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//! .checked_add(1)
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//! .unwrap_or_else(|| abort() ));
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//! }
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//! }
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//!
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//! impl<T: ?Sized> RcInnerPtr<T> for Rc<T> {
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//! fn inner(&self) -> &RcInner<T> {
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//! unsafe {
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//! self.ptr.as_ref()
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//! }
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//! }
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//! }
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//! ```
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//!
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//! [`Arc<T>`]: ../../std/sync/struct.Arc.html
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//! [`Rc<T>`]: ../../std/rc/struct.Rc.html
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//! [`RwLock<T>`]: ../../std/sync/struct.RwLock.html
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//! [`Mutex<T>`]: ../../std/sync/struct.Mutex.html
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//! [`OnceLock<T>`]: ../../std/sync/struct.OnceLock.html
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//! [`LazyLock<T, F>`]: ../../std/sync/struct.LazyLock.html
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//! [`Sync`]: ../../std/marker/trait.Sync.html
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//! [`atomic`]: crate::sync::atomic
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#![stable(feature = "rust1", since = "1.0.0")]
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use crate::cmp::Ordering;
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use crate::fmt::{self, Debug, Display};
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use crate::marker::{PhantomData, PointerLike, Unsize};
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use crate::mem;
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use crate::ops::{CoerceUnsized, Deref, DerefMut, DerefPure, DispatchFromDyn};
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use crate::pin::PinCoerceUnsized;
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use crate::ptr::{self, NonNull};
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mod lazy;
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mod once;
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#[stable(feature = "lazy_cell", since = "1.80.0")]
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pub use lazy::LazyCell;
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#[stable(feature = "once_cell", since = "1.70.0")]
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pub use once::OnceCell;
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/// A mutable memory location.
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///
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/// # Memory layout
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///
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/// `Cell<T>` has the same [memory layout and caveats as
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/// `UnsafeCell<T>`](UnsafeCell#memory-layout). In particular, this means that
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/// `Cell<T>` has the same in-memory representation as its inner type `T`.
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///
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/// # Examples
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///
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/// In this example, you can see that `Cell<T>` enables mutation inside an
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/// immutable struct. In other words, it enables "interior mutability".
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///
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/// ```
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/// use std::cell::Cell;
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///
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/// struct SomeStruct {
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/// regular_field: u8,
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/// special_field: Cell<u8>,
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/// }
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///
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/// let my_struct = SomeStruct {
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/// regular_field: 0,
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/// special_field: Cell::new(1),
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/// };
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///
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/// let new_value = 100;
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///
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/// // ERROR: `my_struct` is immutable
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/// // my_struct.regular_field = new_value;
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///
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/// // WORKS: although `my_struct` is immutable, `special_field` is a `Cell`,
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/// // which can always be mutated
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/// my_struct.special_field.set(new_value);
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/// assert_eq!(my_struct.special_field.get(), new_value);
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/// ```
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///
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/// See the [module-level documentation](self) for more.
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#[rustc_diagnostic_item = "Cell"]
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#[stable(feature = "rust1", since = "1.0.0")]
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#[repr(transparent)]
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#[rustc_pub_transparent]
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pub struct Cell<T: ?Sized> {
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value: UnsafeCell<T>,
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}
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#[stable(feature = "rust1", since = "1.0.0")]
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unsafe impl<T: ?Sized> Send for Cell<T> where T: Send {}
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// Note that this negative impl isn't strictly necessary for correctness,
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// as `Cell` wraps `UnsafeCell`, which is itself `!Sync`.
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// However, given how important `Cell`'s `!Sync`-ness is,
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// having an explicit negative impl is nice for documentation purposes
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// and results in nicer error messages.
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#[stable(feature = "rust1", since = "1.0.0")]
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impl<T: ?Sized> !Sync for Cell<T> {}
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#[stable(feature = "rust1", since = "1.0.0")]
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impl<T: Copy> Clone for Cell<T> {
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#[inline]
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fn clone(&self) -> Cell<T> {
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Cell::new(self.get())
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}
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}
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#[stable(feature = "rust1", since = "1.0.0")]
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impl<T: Default> Default for Cell<T> {
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/// Creates a `Cell<T>`, with the `Default` value for T.
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#[inline]
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fn default() -> Cell<T> {
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Cell::new(Default::default())
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}
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}
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#[stable(feature = "rust1", since = "1.0.0")]
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impl<T: PartialEq + Copy> PartialEq for Cell<T> {
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#[inline]
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fn eq(&self, other: &Cell<T>) -> bool {
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self.get() == other.get()
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}
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}
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#[stable(feature = "cell_eq", since = "1.2.0")]
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impl<T: Eq + Copy> Eq for Cell<T> {}
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#[stable(feature = "cell_ord", since = "1.10.0")]
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impl<T: PartialOrd + Copy> PartialOrd for Cell<T> {
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#[inline]
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fn partial_cmp(&self, other: &Cell<T>) -> Option<Ordering> {
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self.get().partial_cmp(&other.get())
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}
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#[inline]
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fn lt(&self, other: &Cell<T>) -> bool {
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self.get() < other.get()
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}
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#[inline]
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fn le(&self, other: &Cell<T>) -> bool {
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self.get() <= other.get()
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}
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#[inline]
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fn gt(&self, other: &Cell<T>) -> bool {
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self.get() > other.get()
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}
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#[inline]
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fn ge(&self, other: &Cell<T>) -> bool {
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self.get() >= other.get()
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}
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}
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#[stable(feature = "cell_ord", since = "1.10.0")]
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impl<T: Ord + Copy> Ord for Cell<T> {
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#[inline]
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fn cmp(&self, other: &Cell<T>) -> Ordering {
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self.get().cmp(&other.get())
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}
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}
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#[stable(feature = "cell_from", since = "1.12.0")]
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impl<T> From<T> for Cell<T> {
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/// Creates a new `Cell<T>` containing the given value.
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fn from(t: T) -> Cell<T> {
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Cell::new(t)
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}
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}
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impl<T> Cell<T> {
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/// Creates a new `Cell` containing the given value.
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///
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/// # Examples
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///
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/// ```
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/// use std::cell::Cell;
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///
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/// let c = Cell::new(5);
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/// ```
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#[stable(feature = "rust1", since = "1.0.0")]
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#[rustc_const_stable(feature = "const_cell_new", since = "1.24.0")]
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#[inline]
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pub const fn new(value: T) -> Cell<T> {
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Cell { value: UnsafeCell::new(value) }
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}
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/// Sets the contained value.
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///
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/// # Examples
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///
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/// ```
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/// use std::cell::Cell;
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///
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/// let c = Cell::new(5);
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///
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/// c.set(10);
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/// ```
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#[inline]
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#[stable(feature = "rust1", since = "1.0.0")]
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pub fn set(&self, val: T) {
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self.replace(val);
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}
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/// Swaps the values of two `Cell`s.
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///
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/// The difference with `std::mem::swap` is that this function doesn't
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/// require a `&mut` reference.
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///
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|
/// # Panics
|
|
///
|
|
/// This function will panic if `self` and `other` are different `Cell`s that partially overlap.
|
|
/// (Using just standard library methods, it is impossible to create such partially overlapping `Cell`s.
|
|
/// However, unsafe code is allowed to e.g. create two `&Cell<[i32; 2]>` that partially overlap.)
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// use std::cell::Cell;
|
|
///
|
|
/// let c1 = Cell::new(5i32);
|
|
/// let c2 = Cell::new(10i32);
|
|
/// c1.swap(&c2);
|
|
/// assert_eq!(10, c1.get());
|
|
/// assert_eq!(5, c2.get());
|
|
/// ```
|
|
#[inline]
|
|
#[stable(feature = "move_cell", since = "1.17.0")]
|
|
pub fn swap(&self, other: &Self) {
|
|
// This function documents that it *will* panic, and intrinsics::is_nonoverlapping doesn't
|
|
// do the check in const, so trying to use it here would be inviting unnecessary fragility.
|
|
fn is_nonoverlapping<T>(src: *const T, dst: *const T) -> bool {
|
|
let src_usize = src.addr();
|
|
let dst_usize = dst.addr();
|
|
let diff = src_usize.abs_diff(dst_usize);
|
|
diff >= size_of::<T>()
|
|
}
|
|
|
|
if ptr::eq(self, other) {
|
|
// Swapping wouldn't change anything.
|
|
return;
|
|
}
|
|
if !is_nonoverlapping(self, other) {
|
|
// See <https://github.com/rust-lang/rust/issues/80778> for why we need to stop here.
|
|
panic!("`Cell::swap` on overlapping non-identical `Cell`s");
|
|
}
|
|
// SAFETY: This can be risky if called from separate threads, but `Cell`
|
|
// is `!Sync` so this won't happen. This also won't invalidate any
|
|
// pointers since `Cell` makes sure nothing else will be pointing into
|
|
// either of these `Cell`s. We also excluded shenanigans like partially overlapping `Cell`s,
|
|
// so `swap` will just properly copy two full values of type `T` back and forth.
|
|
unsafe {
|
|
mem::swap(&mut *self.value.get(), &mut *other.value.get());
|
|
}
|
|
}
|
|
|
|
/// Replaces the contained value with `val`, and returns the old contained value.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// use std::cell::Cell;
|
|
///
|
|
/// let cell = Cell::new(5);
|
|
/// assert_eq!(cell.get(), 5);
|
|
/// assert_eq!(cell.replace(10), 5);
|
|
/// assert_eq!(cell.get(), 10);
|
|
/// ```
|
|
#[inline]
|
|
#[stable(feature = "move_cell", since = "1.17.0")]
|
|
#[rustc_const_stable(feature = "const_cell", since = "CURRENT_RUSTC_VERSION")]
|
|
#[rustc_confusables("swap")]
|
|
pub const fn replace(&self, val: T) -> T {
|
|
// SAFETY: This can cause data races if called from a separate thread,
|
|
// but `Cell` is `!Sync` so this won't happen.
|
|
mem::replace(unsafe { &mut *self.value.get() }, val)
|
|
}
|
|
|
|
/// Unwraps the value, consuming the cell.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// use std::cell::Cell;
|
|
///
|
|
/// let c = Cell::new(5);
|
|
/// let five = c.into_inner();
|
|
///
|
|
/// assert_eq!(five, 5);
|
|
/// ```
|
|
#[stable(feature = "move_cell", since = "1.17.0")]
|
|
#[rustc_const_stable(feature = "const_cell_into_inner", since = "1.83.0")]
|
|
#[rustc_allow_const_fn_unstable(const_precise_live_drops)]
|
|
pub const fn into_inner(self) -> T {
|
|
self.value.into_inner()
|
|
}
|
|
}
|
|
|
|
impl<T: Copy> Cell<T> {
|
|
/// Returns a copy of the contained value.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// use std::cell::Cell;
|
|
///
|
|
/// let c = Cell::new(5);
|
|
///
|
|
/// let five = c.get();
|
|
/// ```
|
|
#[inline]
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
|
#[rustc_const_stable(feature = "const_cell", since = "CURRENT_RUSTC_VERSION")]
|
|
pub const fn get(&self) -> T {
|
|
// SAFETY: This can cause data races if called from a separate thread,
|
|
// but `Cell` is `!Sync` so this won't happen.
|
|
unsafe { *self.value.get() }
|
|
}
|
|
|
|
/// Updates the contained value using a function.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// #![feature(cell_update)]
|
|
///
|
|
/// use std::cell::Cell;
|
|
///
|
|
/// let c = Cell::new(5);
|
|
/// c.update(|x| x + 1);
|
|
/// assert_eq!(c.get(), 6);
|
|
/// ```
|
|
#[inline]
|
|
#[unstable(feature = "cell_update", issue = "50186")]
|
|
pub fn update(&self, f: impl FnOnce(T) -> T) {
|
|
let old = self.get();
|
|
self.set(f(old));
|
|
}
|
|
}
|
|
|
|
impl<T: ?Sized> Cell<T> {
|
|
/// Returns a raw pointer to the underlying data in this cell.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// use std::cell::Cell;
|
|
///
|
|
/// let c = Cell::new(5);
|
|
///
|
|
/// let ptr = c.as_ptr();
|
|
/// ```
|
|
#[inline]
|
|
#[stable(feature = "cell_as_ptr", since = "1.12.0")]
|
|
#[rustc_const_stable(feature = "const_cell_as_ptr", since = "1.32.0")]
|
|
#[rustc_as_ptr]
|
|
#[rustc_never_returns_null_ptr]
|
|
pub const fn as_ptr(&self) -> *mut T {
|
|
self.value.get()
|
|
}
|
|
|
|
/// Returns a mutable reference to the underlying data.
|
|
///
|
|
/// This call borrows `Cell` mutably (at compile-time) which guarantees
|
|
/// that we possess the only reference.
|
|
///
|
|
/// However be cautious: this method expects `self` to be mutable, which is
|
|
/// generally not the case when using a `Cell`. If you require interior
|
|
/// mutability by reference, consider using `RefCell` which provides
|
|
/// run-time checked mutable borrows through its [`borrow_mut`] method.
|
|
///
|
|
/// [`borrow_mut`]: RefCell::borrow_mut()
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// use std::cell::Cell;
|
|
///
|
|
/// let mut c = Cell::new(5);
|
|
/// *c.get_mut() += 1;
|
|
///
|
|
/// assert_eq!(c.get(), 6);
|
|
/// ```
|
|
#[inline]
|
|
#[stable(feature = "cell_get_mut", since = "1.11.0")]
|
|
#[rustc_const_stable(feature = "const_cell", since = "CURRENT_RUSTC_VERSION")]
|
|
pub const fn get_mut(&mut self) -> &mut T {
|
|
self.value.get_mut()
|
|
}
|
|
|
|
/// Returns a `&Cell<T>` from a `&mut T`
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// use std::cell::Cell;
|
|
///
|
|
/// let slice: &mut [i32] = &mut [1, 2, 3];
|
|
/// let cell_slice: &Cell<[i32]> = Cell::from_mut(slice);
|
|
/// let slice_cell: &[Cell<i32>] = cell_slice.as_slice_of_cells();
|
|
///
|
|
/// assert_eq!(slice_cell.len(), 3);
|
|
/// ```
|
|
#[inline]
|
|
#[stable(feature = "as_cell", since = "1.37.0")]
|
|
#[rustc_const_stable(feature = "const_cell", since = "CURRENT_RUSTC_VERSION")]
|
|
pub const fn from_mut(t: &mut T) -> &Cell<T> {
|
|
// SAFETY: `&mut` ensures unique access.
|
|
unsafe { &*(t as *mut T as *const Cell<T>) }
|
|
}
|
|
}
|
|
|
|
impl<T: Default> Cell<T> {
|
|
/// Takes the value of the cell, leaving `Default::default()` in its place.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// use std::cell::Cell;
|
|
///
|
|
/// let c = Cell::new(5);
|
|
/// let five = c.take();
|
|
///
|
|
/// assert_eq!(five, 5);
|
|
/// assert_eq!(c.into_inner(), 0);
|
|
/// ```
|
|
#[stable(feature = "move_cell", since = "1.17.0")]
|
|
pub fn take(&self) -> T {
|
|
self.replace(Default::default())
|
|
}
|
|
}
|
|
|
|
#[unstable(feature = "coerce_unsized", issue = "18598")]
|
|
impl<T: CoerceUnsized<U>, U> CoerceUnsized<Cell<U>> for Cell<T> {}
|
|
|
|
// Allow types that wrap `Cell` to also implement `DispatchFromDyn`
|
|
// and become dyn-compatible method receivers.
|
|
// Note that currently `Cell` itself cannot be a method receiver
|
|
// because it does not implement Deref.
|
|
// In other words:
|
|
// `self: Cell<&Self>` won't work
|
|
// `self: CellWrapper<Self>` becomes possible
|
|
#[unstable(feature = "dispatch_from_dyn", issue = "none")]
|
|
impl<T: DispatchFromDyn<U>, U> DispatchFromDyn<Cell<U>> for Cell<T> {}
|
|
|
|
#[unstable(feature = "pointer_like_trait", issue = "none")]
|
|
impl<T: PointerLike> PointerLike for Cell<T> {}
|
|
|
|
impl<T> Cell<[T]> {
|
|
/// Returns a `&[Cell<T>]` from a `&Cell<[T]>`
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// use std::cell::Cell;
|
|
///
|
|
/// let slice: &mut [i32] = &mut [1, 2, 3];
|
|
/// let cell_slice: &Cell<[i32]> = Cell::from_mut(slice);
|
|
/// let slice_cell: &[Cell<i32>] = cell_slice.as_slice_of_cells();
|
|
///
|
|
/// assert_eq!(slice_cell.len(), 3);
|
|
/// ```
|
|
#[stable(feature = "as_cell", since = "1.37.0")]
|
|
#[rustc_const_stable(feature = "const_cell", since = "CURRENT_RUSTC_VERSION")]
|
|
pub const fn as_slice_of_cells(&self) -> &[Cell<T>] {
|
|
// SAFETY: `Cell<T>` has the same memory layout as `T`.
|
|
unsafe { &*(self as *const Cell<[T]> as *const [Cell<T>]) }
|
|
}
|
|
}
|
|
|
|
impl<T, const N: usize> Cell<[T; N]> {
|
|
/// Returns a `&[Cell<T>; N]` from a `&Cell<[T; N]>`
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// #![feature(as_array_of_cells)]
|
|
/// use std::cell::Cell;
|
|
///
|
|
/// let mut array: [i32; 3] = [1, 2, 3];
|
|
/// let cell_array: &Cell<[i32; 3]> = Cell::from_mut(&mut array);
|
|
/// let array_cell: &[Cell<i32>; 3] = cell_array.as_array_of_cells();
|
|
/// ```
|
|
#[unstable(feature = "as_array_of_cells", issue = "88248")]
|
|
pub const fn as_array_of_cells(&self) -> &[Cell<T>; N] {
|
|
// SAFETY: `Cell<T>` has the same memory layout as `T`.
|
|
unsafe { &*(self as *const Cell<[T; N]> as *const [Cell<T>; N]) }
|
|
}
|
|
}
|
|
|
|
/// A mutable memory location with dynamically checked borrow rules
|
|
///
|
|
/// See the [module-level documentation](self) for more.
|
|
#[rustc_diagnostic_item = "RefCell"]
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
|
pub struct RefCell<T: ?Sized> {
|
|
borrow: Cell<BorrowFlag>,
|
|
// Stores the location of the earliest currently active borrow.
|
|
// This gets updated whenever we go from having zero borrows
|
|
// to having a single borrow. When a borrow occurs, this gets included
|
|
// in the generated `BorrowError`/`BorrowMutError`
|
|
#[cfg(feature = "debug_refcell")]
|
|
borrowed_at: Cell<Option<&'static crate::panic::Location<'static>>>,
|
|
value: UnsafeCell<T>,
|
|
}
|
|
|
|
/// An error returned by [`RefCell::try_borrow`].
|
|
#[stable(feature = "try_borrow", since = "1.13.0")]
|
|
#[non_exhaustive]
|
|
pub struct BorrowError {
|
|
#[cfg(feature = "debug_refcell")]
|
|
location: &'static crate::panic::Location<'static>,
|
|
}
|
|
|
|
#[stable(feature = "try_borrow", since = "1.13.0")]
|
|
impl Debug for BorrowError {
|
|
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
|
|
let mut builder = f.debug_struct("BorrowError");
|
|
|
|
#[cfg(feature = "debug_refcell")]
|
|
builder.field("location", self.location);
|
|
|
|
builder.finish()
|
|
}
|
|
}
|
|
|
|
#[stable(feature = "try_borrow", since = "1.13.0")]
|
|
impl Display for BorrowError {
|
|
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
|
|
Display::fmt("already mutably borrowed", f)
|
|
}
|
|
}
|
|
|
|
/// An error returned by [`RefCell::try_borrow_mut`].
|
|
#[stable(feature = "try_borrow", since = "1.13.0")]
|
|
#[non_exhaustive]
|
|
pub struct BorrowMutError {
|
|
#[cfg(feature = "debug_refcell")]
|
|
location: &'static crate::panic::Location<'static>,
|
|
}
|
|
|
|
#[stable(feature = "try_borrow", since = "1.13.0")]
|
|
impl Debug for BorrowMutError {
|
|
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
|
|
let mut builder = f.debug_struct("BorrowMutError");
|
|
|
|
#[cfg(feature = "debug_refcell")]
|
|
builder.field("location", self.location);
|
|
|
|
builder.finish()
|
|
}
|
|
}
|
|
|
|
#[stable(feature = "try_borrow", since = "1.13.0")]
|
|
impl Display for BorrowMutError {
|
|
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
|
|
Display::fmt("already borrowed", f)
|
|
}
|
|
}
|
|
|
|
// This ensures the panicking code is outlined from `borrow_mut` for `RefCell`.
|
|
#[cfg_attr(not(feature = "panic_immediate_abort"), inline(never))]
|
|
#[track_caller]
|
|
#[cold]
|
|
fn panic_already_borrowed(err: BorrowMutError) -> ! {
|
|
panic!("already borrowed: {:?}", err)
|
|
}
|
|
|
|
// This ensures the panicking code is outlined from `borrow` for `RefCell`.
|
|
#[cfg_attr(not(feature = "panic_immediate_abort"), inline(never))]
|
|
#[track_caller]
|
|
#[cold]
|
|
fn panic_already_mutably_borrowed(err: BorrowError) -> ! {
|
|
panic!("already mutably borrowed: {:?}", err)
|
|
}
|
|
|
|
// Positive values represent the number of `Ref` active. Negative values
|
|
// represent the number of `RefMut` active. Multiple `RefMut`s can only be
|
|
// active at a time if they refer to distinct, nonoverlapping components of a
|
|
// `RefCell` (e.g., different ranges of a slice).
|
|
//
|
|
// `Ref` and `RefMut` are both two words in size, and so there will likely never
|
|
// be enough `Ref`s or `RefMut`s in existence to overflow half of the `usize`
|
|
// range. Thus, a `BorrowFlag` will probably never overflow or underflow.
|
|
// However, this is not a guarantee, as a pathological program could repeatedly
|
|
// create and then mem::forget `Ref`s or `RefMut`s. Thus, all code must
|
|
// explicitly check for overflow and underflow in order to avoid unsafety, or at
|
|
// least behave correctly in the event that overflow or underflow happens (e.g.,
|
|
// see BorrowRef::new).
|
|
type BorrowFlag = isize;
|
|
const UNUSED: BorrowFlag = 0;
|
|
|
|
#[inline(always)]
|
|
fn is_writing(x: BorrowFlag) -> bool {
|
|
x < UNUSED
|
|
}
|
|
|
|
#[inline(always)]
|
|
fn is_reading(x: BorrowFlag) -> bool {
|
|
x > UNUSED
|
|
}
|
|
|
|
impl<T> RefCell<T> {
|
|
/// Creates a new `RefCell` containing `value`.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// use std::cell::RefCell;
|
|
///
|
|
/// let c = RefCell::new(5);
|
|
/// ```
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
|
#[rustc_const_stable(feature = "const_refcell_new", since = "1.24.0")]
|
|
#[inline]
|
|
pub const fn new(value: T) -> RefCell<T> {
|
|
RefCell {
|
|
value: UnsafeCell::new(value),
|
|
borrow: Cell::new(UNUSED),
|
|
#[cfg(feature = "debug_refcell")]
|
|
borrowed_at: Cell::new(None),
|
|
}
|
|
}
|
|
|
|
/// Consumes the `RefCell`, returning the wrapped value.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// use std::cell::RefCell;
|
|
///
|
|
/// let c = RefCell::new(5);
|
|
///
|
|
/// let five = c.into_inner();
|
|
/// ```
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
|
#[rustc_const_stable(feature = "const_cell_into_inner", since = "1.83.0")]
|
|
#[rustc_allow_const_fn_unstable(const_precise_live_drops)]
|
|
#[inline]
|
|
pub const fn into_inner(self) -> T {
|
|
// Since this function takes `self` (the `RefCell`) by value, the
|
|
// compiler statically verifies that it is not currently borrowed.
|
|
self.value.into_inner()
|
|
}
|
|
|
|
/// Replaces the wrapped value with a new one, returning the old value,
|
|
/// without deinitializing either one.
|
|
///
|
|
/// This function corresponds to [`std::mem::replace`](../mem/fn.replace.html).
|
|
///
|
|
/// # Panics
|
|
///
|
|
/// Panics if the value is currently borrowed.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// use std::cell::RefCell;
|
|
/// let cell = RefCell::new(5);
|
|
/// let old_value = cell.replace(6);
|
|
/// assert_eq!(old_value, 5);
|
|
/// assert_eq!(cell, RefCell::new(6));
|
|
/// ```
|
|
#[inline]
|
|
#[stable(feature = "refcell_replace", since = "1.24.0")]
|
|
#[track_caller]
|
|
#[rustc_confusables("swap")]
|
|
pub fn replace(&self, t: T) -> T {
|
|
mem::replace(&mut *self.borrow_mut(), t)
|
|
}
|
|
|
|
/// Replaces the wrapped value with a new one computed from `f`, returning
|
|
/// the old value, without deinitializing either one.
|
|
///
|
|
/// # Panics
|
|
///
|
|
/// Panics if the value is currently borrowed.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// use std::cell::RefCell;
|
|
/// let cell = RefCell::new(5);
|
|
/// let old_value = cell.replace_with(|&mut old| old + 1);
|
|
/// assert_eq!(old_value, 5);
|
|
/// assert_eq!(cell, RefCell::new(6));
|
|
/// ```
|
|
#[inline]
|
|
#[stable(feature = "refcell_replace_swap", since = "1.35.0")]
|
|
#[track_caller]
|
|
pub fn replace_with<F: FnOnce(&mut T) -> T>(&self, f: F) -> T {
|
|
let mut_borrow = &mut *self.borrow_mut();
|
|
let replacement = f(mut_borrow);
|
|
mem::replace(mut_borrow, replacement)
|
|
}
|
|
|
|
/// Swaps the wrapped value of `self` with the wrapped value of `other`,
|
|
/// without deinitializing either one.
|
|
///
|
|
/// This function corresponds to [`std::mem::swap`](../mem/fn.swap.html).
|
|
///
|
|
/// # Panics
|
|
///
|
|
/// Panics if the value in either `RefCell` is currently borrowed, or
|
|
/// if `self` and `other` point to the same `RefCell`.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// use std::cell::RefCell;
|
|
/// let c = RefCell::new(5);
|
|
/// let d = RefCell::new(6);
|
|
/// c.swap(&d);
|
|
/// assert_eq!(c, RefCell::new(6));
|
|
/// assert_eq!(d, RefCell::new(5));
|
|
/// ```
|
|
#[inline]
|
|
#[stable(feature = "refcell_swap", since = "1.24.0")]
|
|
pub fn swap(&self, other: &Self) {
|
|
mem::swap(&mut *self.borrow_mut(), &mut *other.borrow_mut())
|
|
}
|
|
}
|
|
|
|
impl<T: ?Sized> RefCell<T> {
|
|
/// Immutably borrows the wrapped value.
|
|
///
|
|
/// The borrow lasts until the returned `Ref` exits scope. Multiple
|
|
/// immutable borrows can be taken out at the same time.
|
|
///
|
|
/// # Panics
|
|
///
|
|
/// Panics if the value is currently mutably borrowed. For a non-panicking variant, use
|
|
/// [`try_borrow`](#method.try_borrow).
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// use std::cell::RefCell;
|
|
///
|
|
/// let c = RefCell::new(5);
|
|
///
|
|
/// let borrowed_five = c.borrow();
|
|
/// let borrowed_five2 = c.borrow();
|
|
/// ```
|
|
///
|
|
/// An example of panic:
|
|
///
|
|
/// ```should_panic
|
|
/// use std::cell::RefCell;
|
|
///
|
|
/// let c = RefCell::new(5);
|
|
///
|
|
/// let m = c.borrow_mut();
|
|
/// let b = c.borrow(); // this causes a panic
|
|
/// ```
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
|
#[inline]
|
|
#[track_caller]
|
|
pub fn borrow(&self) -> Ref<'_, T> {
|
|
match self.try_borrow() {
|
|
Ok(b) => b,
|
|
Err(err) => panic_already_mutably_borrowed(err),
|
|
}
|
|
}
|
|
|
|
/// Immutably borrows the wrapped value, returning an error if the value is currently mutably
|
|
/// borrowed.
|
|
///
|
|
/// The borrow lasts until the returned `Ref` exits scope. Multiple immutable borrows can be
|
|
/// taken out at the same time.
|
|
///
|
|
/// This is the non-panicking variant of [`borrow`](#method.borrow).
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// use std::cell::RefCell;
|
|
///
|
|
/// let c = RefCell::new(5);
|
|
///
|
|
/// {
|
|
/// let m = c.borrow_mut();
|
|
/// assert!(c.try_borrow().is_err());
|
|
/// }
|
|
///
|
|
/// {
|
|
/// let m = c.borrow();
|
|
/// assert!(c.try_borrow().is_ok());
|
|
/// }
|
|
/// ```
|
|
#[stable(feature = "try_borrow", since = "1.13.0")]
|
|
#[inline]
|
|
#[cfg_attr(feature = "debug_refcell", track_caller)]
|
|
pub fn try_borrow(&self) -> Result<Ref<'_, T>, BorrowError> {
|
|
match BorrowRef::new(&self.borrow) {
|
|
Some(b) => {
|
|
#[cfg(feature = "debug_refcell")]
|
|
{
|
|
// `borrowed_at` is always the *first* active borrow
|
|
if b.borrow.get() == 1 {
|
|
self.borrowed_at.set(Some(crate::panic::Location::caller()));
|
|
}
|
|
}
|
|
|
|
// SAFETY: `BorrowRef` ensures that there is only immutable access
|
|
// to the value while borrowed.
|
|
let value = unsafe { NonNull::new_unchecked(self.value.get()) };
|
|
Ok(Ref { value, borrow: b })
|
|
}
|
|
None => Err(BorrowError {
|
|
// If a borrow occurred, then we must already have an outstanding borrow,
|
|
// so `borrowed_at` will be `Some`
|
|
#[cfg(feature = "debug_refcell")]
|
|
location: self.borrowed_at.get().unwrap(),
|
|
}),
|
|
}
|
|
}
|
|
|
|
/// Mutably borrows the wrapped value.
|
|
///
|
|
/// The borrow lasts until the returned `RefMut` or all `RefMut`s derived
|
|
/// from it exit scope. The value cannot be borrowed while this borrow is
|
|
/// active.
|
|
///
|
|
/// # Panics
|
|
///
|
|
/// Panics if the value is currently borrowed. For a non-panicking variant, use
|
|
/// [`try_borrow_mut`](#method.try_borrow_mut).
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// use std::cell::RefCell;
|
|
///
|
|
/// let c = RefCell::new("hello".to_owned());
|
|
///
|
|
/// *c.borrow_mut() = "bonjour".to_owned();
|
|
///
|
|
/// assert_eq!(&*c.borrow(), "bonjour");
|
|
/// ```
|
|
///
|
|
/// An example of panic:
|
|
///
|
|
/// ```should_panic
|
|
/// use std::cell::RefCell;
|
|
///
|
|
/// let c = RefCell::new(5);
|
|
/// let m = c.borrow();
|
|
///
|
|
/// let b = c.borrow_mut(); // this causes a panic
|
|
/// ```
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
|
#[inline]
|
|
#[track_caller]
|
|
pub fn borrow_mut(&self) -> RefMut<'_, T> {
|
|
match self.try_borrow_mut() {
|
|
Ok(b) => b,
|
|
Err(err) => panic_already_borrowed(err),
|
|
}
|
|
}
|
|
|
|
/// Mutably borrows the wrapped value, returning an error if the value is currently borrowed.
|
|
///
|
|
/// The borrow lasts until the returned `RefMut` or all `RefMut`s derived
|
|
/// from it exit scope. The value cannot be borrowed while this borrow is
|
|
/// active.
|
|
///
|
|
/// This is the non-panicking variant of [`borrow_mut`](#method.borrow_mut).
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// use std::cell::RefCell;
|
|
///
|
|
/// let c = RefCell::new(5);
|
|
///
|
|
/// {
|
|
/// let m = c.borrow();
|
|
/// assert!(c.try_borrow_mut().is_err());
|
|
/// }
|
|
///
|
|
/// assert!(c.try_borrow_mut().is_ok());
|
|
/// ```
|
|
#[stable(feature = "try_borrow", since = "1.13.0")]
|
|
#[inline]
|
|
#[cfg_attr(feature = "debug_refcell", track_caller)]
|
|
pub fn try_borrow_mut(&self) -> Result<RefMut<'_, T>, BorrowMutError> {
|
|
match BorrowRefMut::new(&self.borrow) {
|
|
Some(b) => {
|
|
#[cfg(feature = "debug_refcell")]
|
|
{
|
|
self.borrowed_at.set(Some(crate::panic::Location::caller()));
|
|
}
|
|
|
|
// SAFETY: `BorrowRefMut` guarantees unique access.
|
|
let value = unsafe { NonNull::new_unchecked(self.value.get()) };
|
|
Ok(RefMut { value, borrow: b, marker: PhantomData })
|
|
}
|
|
None => Err(BorrowMutError {
|
|
// If a borrow occurred, then we must already have an outstanding borrow,
|
|
// so `borrowed_at` will be `Some`
|
|
#[cfg(feature = "debug_refcell")]
|
|
location: self.borrowed_at.get().unwrap(),
|
|
}),
|
|
}
|
|
}
|
|
|
|
/// Returns a raw pointer to the underlying data in this cell.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// use std::cell::RefCell;
|
|
///
|
|
/// let c = RefCell::new(5);
|
|
///
|
|
/// let ptr = c.as_ptr();
|
|
/// ```
|
|
#[inline]
|
|
#[stable(feature = "cell_as_ptr", since = "1.12.0")]
|
|
#[rustc_as_ptr]
|
|
#[rustc_never_returns_null_ptr]
|
|
pub fn as_ptr(&self) -> *mut T {
|
|
self.value.get()
|
|
}
|
|
|
|
/// Returns a mutable reference to the underlying data.
|
|
///
|
|
/// Since this method borrows `RefCell` mutably, it is statically guaranteed
|
|
/// that no borrows to the underlying data exist. The dynamic checks inherent
|
|
/// in [`borrow_mut`] and most other methods of `RefCell` are therefore
|
|
/// unnecessary. Note that this method does not reset the borrowing state if borrows were previously leaked
|
|
/// (e.g., via [`forget()`] on a [`Ref`] or [`RefMut`]). For that purpose,
|
|
/// consider using the unstable [`undo_leak`] method.
|
|
///
|
|
/// This method can only be called if `RefCell` can be mutably borrowed,
|
|
/// which in general is only the case directly after the `RefCell` has
|
|
/// been created. In these situations, skipping the aforementioned dynamic
|
|
/// borrowing checks may yield better ergonomics and runtime-performance.
|
|
///
|
|
/// In most situations where `RefCell` is used, it can't be borrowed mutably.
|
|
/// Use [`borrow_mut`] to get mutable access to the underlying data then.
|
|
///
|
|
/// [`borrow_mut`]: RefCell::borrow_mut()
|
|
/// [`forget()`]: mem::forget
|
|
/// [`undo_leak`]: RefCell::undo_leak()
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// use std::cell::RefCell;
|
|
///
|
|
/// let mut c = RefCell::new(5);
|
|
/// *c.get_mut() += 1;
|
|
///
|
|
/// assert_eq!(c, RefCell::new(6));
|
|
/// ```
|
|
#[inline]
|
|
#[stable(feature = "cell_get_mut", since = "1.11.0")]
|
|
pub fn get_mut(&mut self) -> &mut T {
|
|
self.value.get_mut()
|
|
}
|
|
|
|
/// Undo the effect of leaked guards on the borrow state of the `RefCell`.
|
|
///
|
|
/// This call is similar to [`get_mut`] but more specialized. It borrows `RefCell` mutably to
|
|
/// ensure no borrows exist and then resets the state tracking shared borrows. This is relevant
|
|
/// if some `Ref` or `RefMut` borrows have been leaked.
|
|
///
|
|
/// [`get_mut`]: RefCell::get_mut()
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// #![feature(cell_leak)]
|
|
/// use std::cell::RefCell;
|
|
///
|
|
/// let mut c = RefCell::new(0);
|
|
/// std::mem::forget(c.borrow_mut());
|
|
///
|
|
/// assert!(c.try_borrow().is_err());
|
|
/// c.undo_leak();
|
|
/// assert!(c.try_borrow().is_ok());
|
|
/// ```
|
|
#[unstable(feature = "cell_leak", issue = "69099")]
|
|
pub fn undo_leak(&mut self) -> &mut T {
|
|
*self.borrow.get_mut() = UNUSED;
|
|
self.get_mut()
|
|
}
|
|
|
|
/// Immutably borrows the wrapped value, returning an error if the value is
|
|
/// currently mutably borrowed.
|
|
///
|
|
/// # Safety
|
|
///
|
|
/// Unlike `RefCell::borrow`, this method is unsafe because it does not
|
|
/// return a `Ref`, thus leaving the borrow flag untouched. Mutably
|
|
/// borrowing the `RefCell` while the reference returned by this method
|
|
/// is alive is undefined behavior.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// use std::cell::RefCell;
|
|
///
|
|
/// let c = RefCell::new(5);
|
|
///
|
|
/// {
|
|
/// let m = c.borrow_mut();
|
|
/// assert!(unsafe { c.try_borrow_unguarded() }.is_err());
|
|
/// }
|
|
///
|
|
/// {
|
|
/// let m = c.borrow();
|
|
/// assert!(unsafe { c.try_borrow_unguarded() }.is_ok());
|
|
/// }
|
|
/// ```
|
|
#[stable(feature = "borrow_state", since = "1.37.0")]
|
|
#[inline]
|
|
pub unsafe fn try_borrow_unguarded(&self) -> Result<&T, BorrowError> {
|
|
if !is_writing(self.borrow.get()) {
|
|
// SAFETY: We check that nobody is actively writing now, but it is
|
|
// the caller's responsibility to ensure that nobody writes until
|
|
// the returned reference is no longer in use.
|
|
// Also, `self.value.get()` refers to the value owned by `self`
|
|
// and is thus guaranteed to be valid for the lifetime of `self`.
|
|
Ok(unsafe { &*self.value.get() })
|
|
} else {
|
|
Err(BorrowError {
|
|
// If a borrow occurred, then we must already have an outstanding borrow,
|
|
// so `borrowed_at` will be `Some`
|
|
#[cfg(feature = "debug_refcell")]
|
|
location: self.borrowed_at.get().unwrap(),
|
|
})
|
|
}
|
|
}
|
|
}
|
|
|
|
impl<T: Default> RefCell<T> {
|
|
/// Takes the wrapped value, leaving `Default::default()` in its place.
|
|
///
|
|
/// # Panics
|
|
///
|
|
/// Panics if the value is currently borrowed.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// use std::cell::RefCell;
|
|
///
|
|
/// let c = RefCell::new(5);
|
|
/// let five = c.take();
|
|
///
|
|
/// assert_eq!(five, 5);
|
|
/// assert_eq!(c.into_inner(), 0);
|
|
/// ```
|
|
#[stable(feature = "refcell_take", since = "1.50.0")]
|
|
pub fn take(&self) -> T {
|
|
self.replace(Default::default())
|
|
}
|
|
}
|
|
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
|
unsafe impl<T: ?Sized> Send for RefCell<T> where T: Send {}
|
|
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
|
impl<T: ?Sized> !Sync for RefCell<T> {}
|
|
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
|
impl<T: Clone> Clone for RefCell<T> {
|
|
/// # Panics
|
|
///
|
|
/// Panics if the value is currently mutably borrowed.
|
|
#[inline]
|
|
#[track_caller]
|
|
fn clone(&self) -> RefCell<T> {
|
|
RefCell::new(self.borrow().clone())
|
|
}
|
|
|
|
/// # Panics
|
|
///
|
|
/// Panics if `source` is currently mutably borrowed.
|
|
#[inline]
|
|
#[track_caller]
|
|
fn clone_from(&mut self, source: &Self) {
|
|
self.get_mut().clone_from(&source.borrow())
|
|
}
|
|
}
|
|
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
|
impl<T: Default> Default for RefCell<T> {
|
|
/// Creates a `RefCell<T>`, with the `Default` value for T.
|
|
#[inline]
|
|
fn default() -> RefCell<T> {
|
|
RefCell::new(Default::default())
|
|
}
|
|
}
|
|
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
|
impl<T: ?Sized + PartialEq> PartialEq for RefCell<T> {
|
|
/// # Panics
|
|
///
|
|
/// Panics if the value in either `RefCell` is currently mutably borrowed.
|
|
#[inline]
|
|
fn eq(&self, other: &RefCell<T>) -> bool {
|
|
*self.borrow() == *other.borrow()
|
|
}
|
|
}
|
|
|
|
#[stable(feature = "cell_eq", since = "1.2.0")]
|
|
impl<T: ?Sized + Eq> Eq for RefCell<T> {}
|
|
|
|
#[stable(feature = "cell_ord", since = "1.10.0")]
|
|
impl<T: ?Sized + PartialOrd> PartialOrd for RefCell<T> {
|
|
/// # Panics
|
|
///
|
|
/// Panics if the value in either `RefCell` is currently mutably borrowed.
|
|
#[inline]
|
|
fn partial_cmp(&self, other: &RefCell<T>) -> Option<Ordering> {
|
|
self.borrow().partial_cmp(&*other.borrow())
|
|
}
|
|
|
|
/// # Panics
|
|
///
|
|
/// Panics if the value in either `RefCell` is currently mutably borrowed.
|
|
#[inline]
|
|
fn lt(&self, other: &RefCell<T>) -> bool {
|
|
*self.borrow() < *other.borrow()
|
|
}
|
|
|
|
/// # Panics
|
|
///
|
|
/// Panics if the value in either `RefCell` is currently mutably borrowed.
|
|
#[inline]
|
|
fn le(&self, other: &RefCell<T>) -> bool {
|
|
*self.borrow() <= *other.borrow()
|
|
}
|
|
|
|
/// # Panics
|
|
///
|
|
/// Panics if the value in either `RefCell` is currently mutably borrowed.
|
|
#[inline]
|
|
fn gt(&self, other: &RefCell<T>) -> bool {
|
|
*self.borrow() > *other.borrow()
|
|
}
|
|
|
|
/// # Panics
|
|
///
|
|
/// Panics if the value in either `RefCell` is currently mutably borrowed.
|
|
#[inline]
|
|
fn ge(&self, other: &RefCell<T>) -> bool {
|
|
*self.borrow() >= *other.borrow()
|
|
}
|
|
}
|
|
|
|
#[stable(feature = "cell_ord", since = "1.10.0")]
|
|
impl<T: ?Sized + Ord> Ord for RefCell<T> {
|
|
/// # Panics
|
|
///
|
|
/// Panics if the value in either `RefCell` is currently mutably borrowed.
|
|
#[inline]
|
|
fn cmp(&self, other: &RefCell<T>) -> Ordering {
|
|
self.borrow().cmp(&*other.borrow())
|
|
}
|
|
}
|
|
|
|
#[stable(feature = "cell_from", since = "1.12.0")]
|
|
impl<T> From<T> for RefCell<T> {
|
|
/// Creates a new `RefCell<T>` containing the given value.
|
|
fn from(t: T) -> RefCell<T> {
|
|
RefCell::new(t)
|
|
}
|
|
}
|
|
|
|
#[unstable(feature = "coerce_unsized", issue = "18598")]
|
|
impl<T: CoerceUnsized<U>, U> CoerceUnsized<RefCell<U>> for RefCell<T> {}
|
|
|
|
struct BorrowRef<'b> {
|
|
borrow: &'b Cell<BorrowFlag>,
|
|
}
|
|
|
|
impl<'b> BorrowRef<'b> {
|
|
#[inline]
|
|
fn new(borrow: &'b Cell<BorrowFlag>) -> Option<BorrowRef<'b>> {
|
|
let b = borrow.get().wrapping_add(1);
|
|
if !is_reading(b) {
|
|
// Incrementing borrow can result in a non-reading value (<= 0) in these cases:
|
|
// 1. It was < 0, i.e. there are writing borrows, so we can't allow a read borrow
|
|
// due to Rust's reference aliasing rules
|
|
// 2. It was isize::MAX (the max amount of reading borrows) and it overflowed
|
|
// into isize::MIN (the max amount of writing borrows) so we can't allow
|
|
// an additional read borrow because isize can't represent so many read borrows
|
|
// (this can only happen if you mem::forget more than a small constant amount of
|
|
// `Ref`s, which is not good practice)
|
|
None
|
|
} else {
|
|
// Incrementing borrow can result in a reading value (> 0) in these cases:
|
|
// 1. It was = 0, i.e. it wasn't borrowed, and we are taking the first read borrow
|
|
// 2. It was > 0 and < isize::MAX, i.e. there were read borrows, and isize
|
|
// is large enough to represent having one more read borrow
|
|
borrow.set(b);
|
|
Some(BorrowRef { borrow })
|
|
}
|
|
}
|
|
}
|
|
|
|
impl Drop for BorrowRef<'_> {
|
|
#[inline]
|
|
fn drop(&mut self) {
|
|
let borrow = self.borrow.get();
|
|
debug_assert!(is_reading(borrow));
|
|
self.borrow.set(borrow - 1);
|
|
}
|
|
}
|
|
|
|
impl Clone for BorrowRef<'_> {
|
|
#[inline]
|
|
fn clone(&self) -> Self {
|
|
// Since this Ref exists, we know the borrow flag
|
|
// is a reading borrow.
|
|
let borrow = self.borrow.get();
|
|
debug_assert!(is_reading(borrow));
|
|
// Prevent the borrow counter from overflowing into
|
|
// a writing borrow.
|
|
assert!(borrow != BorrowFlag::MAX);
|
|
self.borrow.set(borrow + 1);
|
|
BorrowRef { borrow: self.borrow }
|
|
}
|
|
}
|
|
|
|
/// Wraps a borrowed reference to a value in a `RefCell` box.
|
|
/// A wrapper type for an immutably borrowed value from a `RefCell<T>`.
|
|
///
|
|
/// See the [module-level documentation](self) for more.
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
|
#[must_not_suspend = "holding a Ref across suspend points can cause BorrowErrors"]
|
|
#[rustc_diagnostic_item = "RefCellRef"]
|
|
pub struct Ref<'b, T: ?Sized + 'b> {
|
|
// NB: we use a pointer instead of `&'b T` to avoid `noalias` violations, because a
|
|
// `Ref` argument doesn't hold immutability for its whole scope, only until it drops.
|
|
// `NonNull` is also covariant over `T`, just like we would have with `&T`.
|
|
value: NonNull<T>,
|
|
borrow: BorrowRef<'b>,
|
|
}
|
|
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
|
impl<T: ?Sized> Deref for Ref<'_, T> {
|
|
type Target = T;
|
|
|
|
#[inline]
|
|
fn deref(&self) -> &T {
|
|
// SAFETY: the value is accessible as long as we hold our borrow.
|
|
unsafe { self.value.as_ref() }
|
|
}
|
|
}
|
|
|
|
#[unstable(feature = "deref_pure_trait", issue = "87121")]
|
|
unsafe impl<T: ?Sized> DerefPure for Ref<'_, T> {}
|
|
|
|
impl<'b, T: ?Sized> Ref<'b, T> {
|
|
/// Copies a `Ref`.
|
|
///
|
|
/// The `RefCell` is already immutably borrowed, so this cannot fail.
|
|
///
|
|
/// This is an associated function that needs to be used as
|
|
/// `Ref::clone(...)`. A `Clone` implementation or a method would interfere
|
|
/// with the widespread use of `r.borrow().clone()` to clone the contents of
|
|
/// a `RefCell`.
|
|
#[stable(feature = "cell_extras", since = "1.15.0")]
|
|
#[must_use]
|
|
#[inline]
|
|
pub fn clone(orig: &Ref<'b, T>) -> Ref<'b, T> {
|
|
Ref { value: orig.value, borrow: orig.borrow.clone() }
|
|
}
|
|
|
|
/// Makes a new `Ref` for a component of the borrowed data.
|
|
///
|
|
/// The `RefCell` is already immutably borrowed, so this cannot fail.
|
|
///
|
|
/// This is an associated function that needs to be used as `Ref::map(...)`.
|
|
/// A method would interfere with methods of the same name on the contents
|
|
/// of a `RefCell` used through `Deref`.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// use std::cell::{RefCell, Ref};
|
|
///
|
|
/// let c = RefCell::new((5, 'b'));
|
|
/// let b1: Ref<'_, (u32, char)> = c.borrow();
|
|
/// let b2: Ref<'_, u32> = Ref::map(b1, |t| &t.0);
|
|
/// assert_eq!(*b2, 5)
|
|
/// ```
|
|
#[stable(feature = "cell_map", since = "1.8.0")]
|
|
#[inline]
|
|
pub fn map<U: ?Sized, F>(orig: Ref<'b, T>, f: F) -> Ref<'b, U>
|
|
where
|
|
F: FnOnce(&T) -> &U,
|
|
{
|
|
Ref { value: NonNull::from(f(&*orig)), borrow: orig.borrow }
|
|
}
|
|
|
|
/// Makes a new `Ref` for an optional component of the borrowed data. The
|
|
/// original guard is returned as an `Err(..)` if the closure returns
|
|
/// `None`.
|
|
///
|
|
/// The `RefCell` is already immutably borrowed, so this cannot fail.
|
|
///
|
|
/// This is an associated function that needs to be used as
|
|
/// `Ref::filter_map(...)`. A method would interfere with methods of the same
|
|
/// name on the contents of a `RefCell` used through `Deref`.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// use std::cell::{RefCell, Ref};
|
|
///
|
|
/// let c = RefCell::new(vec![1, 2, 3]);
|
|
/// let b1: Ref<'_, Vec<u32>> = c.borrow();
|
|
/// let b2: Result<Ref<'_, u32>, _> = Ref::filter_map(b1, |v| v.get(1));
|
|
/// assert_eq!(*b2.unwrap(), 2);
|
|
/// ```
|
|
#[stable(feature = "cell_filter_map", since = "1.63.0")]
|
|
#[inline]
|
|
pub fn filter_map<U: ?Sized, F>(orig: Ref<'b, T>, f: F) -> Result<Ref<'b, U>, Self>
|
|
where
|
|
F: FnOnce(&T) -> Option<&U>,
|
|
{
|
|
match f(&*orig) {
|
|
Some(value) => Ok(Ref { value: NonNull::from(value), borrow: orig.borrow }),
|
|
None => Err(orig),
|
|
}
|
|
}
|
|
|
|
/// Splits a `Ref` into multiple `Ref`s for different components of the
|
|
/// borrowed data.
|
|
///
|
|
/// The `RefCell` is already immutably borrowed, so this cannot fail.
|
|
///
|
|
/// This is an associated function that needs to be used as
|
|
/// `Ref::map_split(...)`. A method would interfere with methods of the same
|
|
/// name on the contents of a `RefCell` used through `Deref`.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// use std::cell::{Ref, RefCell};
|
|
///
|
|
/// let cell = RefCell::new([1, 2, 3, 4]);
|
|
/// let borrow = cell.borrow();
|
|
/// let (begin, end) = Ref::map_split(borrow, |slice| slice.split_at(2));
|
|
/// assert_eq!(*begin, [1, 2]);
|
|
/// assert_eq!(*end, [3, 4]);
|
|
/// ```
|
|
#[stable(feature = "refcell_map_split", since = "1.35.0")]
|
|
#[inline]
|
|
pub fn map_split<U: ?Sized, V: ?Sized, F>(orig: Ref<'b, T>, f: F) -> (Ref<'b, U>, Ref<'b, V>)
|
|
where
|
|
F: FnOnce(&T) -> (&U, &V),
|
|
{
|
|
let (a, b) = f(&*orig);
|
|
let borrow = orig.borrow.clone();
|
|
(
|
|
Ref { value: NonNull::from(a), borrow },
|
|
Ref { value: NonNull::from(b), borrow: orig.borrow },
|
|
)
|
|
}
|
|
|
|
/// Converts into a reference to the underlying data.
|
|
///
|
|
/// The underlying `RefCell` can never be mutably borrowed from again and will always appear
|
|
/// already immutably borrowed. It is not a good idea to leak more than a constant number of
|
|
/// references. The `RefCell` can be immutably borrowed again if only a smaller number of leaks
|
|
/// have occurred in total.
|
|
///
|
|
/// This is an associated function that needs to be used as
|
|
/// `Ref::leak(...)`. A method would interfere with methods of the
|
|
/// same name on the contents of a `RefCell` used through `Deref`.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// #![feature(cell_leak)]
|
|
/// use std::cell::{RefCell, Ref};
|
|
/// let cell = RefCell::new(0);
|
|
///
|
|
/// let value = Ref::leak(cell.borrow());
|
|
/// assert_eq!(*value, 0);
|
|
///
|
|
/// assert!(cell.try_borrow().is_ok());
|
|
/// assert!(cell.try_borrow_mut().is_err());
|
|
/// ```
|
|
#[unstable(feature = "cell_leak", issue = "69099")]
|
|
pub fn leak(orig: Ref<'b, T>) -> &'b T {
|
|
// By forgetting this Ref we ensure that the borrow counter in the RefCell can't go back to
|
|
// UNUSED within the lifetime `'b`. Resetting the reference tracking state would require a
|
|
// unique reference to the borrowed RefCell. No further mutable references can be created
|
|
// from the original cell.
|
|
mem::forget(orig.borrow);
|
|
// SAFETY: after forgetting, we can form a reference for the rest of lifetime `'b`.
|
|
unsafe { orig.value.as_ref() }
|
|
}
|
|
}
|
|
|
|
#[unstable(feature = "coerce_unsized", issue = "18598")]
|
|
impl<'b, T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<Ref<'b, U>> for Ref<'b, T> {}
|
|
|
|
#[stable(feature = "std_guard_impls", since = "1.20.0")]
|
|
impl<T: ?Sized + fmt::Display> fmt::Display for Ref<'_, T> {
|
|
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
|
|
(**self).fmt(f)
|
|
}
|
|
}
|
|
|
|
impl<'b, T: ?Sized> RefMut<'b, T> {
|
|
/// Makes a new `RefMut` for a component of the borrowed data, e.g., an enum
|
|
/// variant.
|
|
///
|
|
/// The `RefCell` is already mutably borrowed, so this cannot fail.
|
|
///
|
|
/// This is an associated function that needs to be used as
|
|
/// `RefMut::map(...)`. A method would interfere with methods of the same
|
|
/// name on the contents of a `RefCell` used through `Deref`.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// use std::cell::{RefCell, RefMut};
|
|
///
|
|
/// let c = RefCell::new((5, 'b'));
|
|
/// {
|
|
/// let b1: RefMut<'_, (u32, char)> = c.borrow_mut();
|
|
/// let mut b2: RefMut<'_, u32> = RefMut::map(b1, |t| &mut t.0);
|
|
/// assert_eq!(*b2, 5);
|
|
/// *b2 = 42;
|
|
/// }
|
|
/// assert_eq!(*c.borrow(), (42, 'b'));
|
|
/// ```
|
|
#[stable(feature = "cell_map", since = "1.8.0")]
|
|
#[inline]
|
|
pub fn map<U: ?Sized, F>(mut orig: RefMut<'b, T>, f: F) -> RefMut<'b, U>
|
|
where
|
|
F: FnOnce(&mut T) -> &mut U,
|
|
{
|
|
let value = NonNull::from(f(&mut *orig));
|
|
RefMut { value, borrow: orig.borrow, marker: PhantomData }
|
|
}
|
|
|
|
/// Makes a new `RefMut` for an optional component of the borrowed data. The
|
|
/// original guard is returned as an `Err(..)` if the closure returns
|
|
/// `None`.
|
|
///
|
|
/// The `RefCell` is already mutably borrowed, so this cannot fail.
|
|
///
|
|
/// This is an associated function that needs to be used as
|
|
/// `RefMut::filter_map(...)`. A method would interfere with methods of the
|
|
/// same name on the contents of a `RefCell` used through `Deref`.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// use std::cell::{RefCell, RefMut};
|
|
///
|
|
/// let c = RefCell::new(vec![1, 2, 3]);
|
|
///
|
|
/// {
|
|
/// let b1: RefMut<'_, Vec<u32>> = c.borrow_mut();
|
|
/// let mut b2: Result<RefMut<'_, u32>, _> = RefMut::filter_map(b1, |v| v.get_mut(1));
|
|
///
|
|
/// if let Ok(mut b2) = b2 {
|
|
/// *b2 += 2;
|
|
/// }
|
|
/// }
|
|
///
|
|
/// assert_eq!(*c.borrow(), vec![1, 4, 3]);
|
|
/// ```
|
|
#[stable(feature = "cell_filter_map", since = "1.63.0")]
|
|
#[inline]
|
|
pub fn filter_map<U: ?Sized, F>(mut orig: RefMut<'b, T>, f: F) -> Result<RefMut<'b, U>, Self>
|
|
where
|
|
F: FnOnce(&mut T) -> Option<&mut U>,
|
|
{
|
|
// SAFETY: function holds onto an exclusive reference for the duration
|
|
// of its call through `orig`, and the pointer is only de-referenced
|
|
// inside of the function call never allowing the exclusive reference to
|
|
// escape.
|
|
match f(&mut *orig) {
|
|
Some(value) => {
|
|
Ok(RefMut { value: NonNull::from(value), borrow: orig.borrow, marker: PhantomData })
|
|
}
|
|
None => Err(orig),
|
|
}
|
|
}
|
|
|
|
/// Splits a `RefMut` into multiple `RefMut`s for different components of the
|
|
/// borrowed data.
|
|
///
|
|
/// The underlying `RefCell` will remain mutably borrowed until both
|
|
/// returned `RefMut`s go out of scope.
|
|
///
|
|
/// The `RefCell` is already mutably borrowed, so this cannot fail.
|
|
///
|
|
/// This is an associated function that needs to be used as
|
|
/// `RefMut::map_split(...)`. A method would interfere with methods of the
|
|
/// same name on the contents of a `RefCell` used through `Deref`.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// use std::cell::{RefCell, RefMut};
|
|
///
|
|
/// let cell = RefCell::new([1, 2, 3, 4]);
|
|
/// let borrow = cell.borrow_mut();
|
|
/// let (mut begin, mut end) = RefMut::map_split(borrow, |slice| slice.split_at_mut(2));
|
|
/// assert_eq!(*begin, [1, 2]);
|
|
/// assert_eq!(*end, [3, 4]);
|
|
/// begin.copy_from_slice(&[4, 3]);
|
|
/// end.copy_from_slice(&[2, 1]);
|
|
/// ```
|
|
#[stable(feature = "refcell_map_split", since = "1.35.0")]
|
|
#[inline]
|
|
pub fn map_split<U: ?Sized, V: ?Sized, F>(
|
|
mut orig: RefMut<'b, T>,
|
|
f: F,
|
|
) -> (RefMut<'b, U>, RefMut<'b, V>)
|
|
where
|
|
F: FnOnce(&mut T) -> (&mut U, &mut V),
|
|
{
|
|
let borrow = orig.borrow.clone();
|
|
let (a, b) = f(&mut *orig);
|
|
(
|
|
RefMut { value: NonNull::from(a), borrow, marker: PhantomData },
|
|
RefMut { value: NonNull::from(b), borrow: orig.borrow, marker: PhantomData },
|
|
)
|
|
}
|
|
|
|
/// Converts into a mutable reference to the underlying data.
|
|
///
|
|
/// The underlying `RefCell` can not be borrowed from again and will always appear already
|
|
/// mutably borrowed, making the returned reference the only to the interior.
|
|
///
|
|
/// This is an associated function that needs to be used as
|
|
/// `RefMut::leak(...)`. A method would interfere with methods of the
|
|
/// same name on the contents of a `RefCell` used through `Deref`.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// #![feature(cell_leak)]
|
|
/// use std::cell::{RefCell, RefMut};
|
|
/// let cell = RefCell::new(0);
|
|
///
|
|
/// let value = RefMut::leak(cell.borrow_mut());
|
|
/// assert_eq!(*value, 0);
|
|
/// *value = 1;
|
|
///
|
|
/// assert!(cell.try_borrow_mut().is_err());
|
|
/// ```
|
|
#[unstable(feature = "cell_leak", issue = "69099")]
|
|
pub fn leak(mut orig: RefMut<'b, T>) -> &'b mut T {
|
|
// By forgetting this BorrowRefMut we ensure that the borrow counter in the RefCell can't
|
|
// go back to UNUSED within the lifetime `'b`. Resetting the reference tracking state would
|
|
// require a unique reference to the borrowed RefCell. No further references can be created
|
|
// from the original cell within that lifetime, making the current borrow the only
|
|
// reference for the remaining lifetime.
|
|
mem::forget(orig.borrow);
|
|
// SAFETY: after forgetting, we can form a reference for the rest of lifetime `'b`.
|
|
unsafe { orig.value.as_mut() }
|
|
}
|
|
}
|
|
|
|
struct BorrowRefMut<'b> {
|
|
borrow: &'b Cell<BorrowFlag>,
|
|
}
|
|
|
|
impl Drop for BorrowRefMut<'_> {
|
|
#[inline]
|
|
fn drop(&mut self) {
|
|
let borrow = self.borrow.get();
|
|
debug_assert!(is_writing(borrow));
|
|
self.borrow.set(borrow + 1);
|
|
}
|
|
}
|
|
|
|
impl<'b> BorrowRefMut<'b> {
|
|
#[inline]
|
|
fn new(borrow: &'b Cell<BorrowFlag>) -> Option<BorrowRefMut<'b>> {
|
|
// NOTE: Unlike BorrowRefMut::clone, new is called to create the initial
|
|
// mutable reference, and so there must currently be no existing
|
|
// references. Thus, while clone increments the mutable refcount, here
|
|
// we explicitly only allow going from UNUSED to UNUSED - 1.
|
|
match borrow.get() {
|
|
UNUSED => {
|
|
borrow.set(UNUSED - 1);
|
|
Some(BorrowRefMut { borrow })
|
|
}
|
|
_ => None,
|
|
}
|
|
}
|
|
|
|
// Clones a `BorrowRefMut`.
|
|
//
|
|
// This is only valid if each `BorrowRefMut` is used to track a mutable
|
|
// reference to a distinct, nonoverlapping range of the original object.
|
|
// This isn't in a Clone impl so that code doesn't call this implicitly.
|
|
#[inline]
|
|
fn clone(&self) -> BorrowRefMut<'b> {
|
|
let borrow = self.borrow.get();
|
|
debug_assert!(is_writing(borrow));
|
|
// Prevent the borrow counter from underflowing.
|
|
assert!(borrow != BorrowFlag::MIN);
|
|
self.borrow.set(borrow - 1);
|
|
BorrowRefMut { borrow: self.borrow }
|
|
}
|
|
}
|
|
|
|
/// A wrapper type for a mutably borrowed value from a `RefCell<T>`.
|
|
///
|
|
/// See the [module-level documentation](self) for more.
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
|
#[must_not_suspend = "holding a RefMut across suspend points can cause BorrowErrors"]
|
|
#[rustc_diagnostic_item = "RefCellRefMut"]
|
|
pub struct RefMut<'b, T: ?Sized + 'b> {
|
|
// NB: we use a pointer instead of `&'b mut T` to avoid `noalias` violations, because a
|
|
// `RefMut` argument doesn't hold exclusivity for its whole scope, only until it drops.
|
|
value: NonNull<T>,
|
|
borrow: BorrowRefMut<'b>,
|
|
// `NonNull` is covariant over `T`, so we need to reintroduce invariance.
|
|
marker: PhantomData<&'b mut T>,
|
|
}
|
|
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
|
impl<T: ?Sized> Deref for RefMut<'_, T> {
|
|
type Target = T;
|
|
|
|
#[inline]
|
|
fn deref(&self) -> &T {
|
|
// SAFETY: the value is accessible as long as we hold our borrow.
|
|
unsafe { self.value.as_ref() }
|
|
}
|
|
}
|
|
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
|
impl<T: ?Sized> DerefMut for RefMut<'_, T> {
|
|
#[inline]
|
|
fn deref_mut(&mut self) -> &mut T {
|
|
// SAFETY: the value is accessible as long as we hold our borrow.
|
|
unsafe { self.value.as_mut() }
|
|
}
|
|
}
|
|
|
|
#[unstable(feature = "deref_pure_trait", issue = "87121")]
|
|
unsafe impl<T: ?Sized> DerefPure for RefMut<'_, T> {}
|
|
|
|
#[unstable(feature = "coerce_unsized", issue = "18598")]
|
|
impl<'b, T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<RefMut<'b, U>> for RefMut<'b, T> {}
|
|
|
|
#[stable(feature = "std_guard_impls", since = "1.20.0")]
|
|
impl<T: ?Sized + fmt::Display> fmt::Display for RefMut<'_, T> {
|
|
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
|
|
(**self).fmt(f)
|
|
}
|
|
}
|
|
|
|
/// The core primitive for interior mutability in Rust.
|
|
///
|
|
/// If you have a reference `&T`, then normally in Rust the compiler performs optimizations based on
|
|
/// the knowledge that `&T` points to immutable data. Mutating that data, for example through an
|
|
/// alias or by transmuting a `&T` into a `&mut T`, is considered undefined behavior.
|
|
/// `UnsafeCell<T>` opts-out of the immutability guarantee for `&T`: a shared reference
|
|
/// `&UnsafeCell<T>` may point to data that is being mutated. This is called "interior mutability".
|
|
///
|
|
/// All other types that allow internal mutability, such as [`Cell<T>`] and [`RefCell<T>`], internally
|
|
/// use `UnsafeCell` to wrap their data.
|
|
///
|
|
/// Note that only the immutability guarantee for shared references is affected by `UnsafeCell`. The
|
|
/// uniqueness guarantee for mutable references is unaffected. There is *no* legal way to obtain
|
|
/// aliasing `&mut`, not even with `UnsafeCell<T>`.
|
|
///
|
|
/// `UnsafeCell` does nothing to avoid data races; they are still undefined behavior. If multiple
|
|
/// threads have access to the same `UnsafeCell`, they must follow the usual rules of the
|
|
/// [concurrent memory model]: conflicting non-synchronized accesses must be done via the APIs in
|
|
/// [`core::sync::atomic`].
|
|
///
|
|
/// The `UnsafeCell` API itself is technically very simple: [`.get()`] gives you a raw pointer
|
|
/// `*mut T` to its contents. It is up to _you_ as the abstraction designer to use that raw pointer
|
|
/// correctly.
|
|
///
|
|
/// [`.get()`]: `UnsafeCell::get`
|
|
/// [concurrent memory model]: ../sync/atomic/index.html#memory-model-for-atomic-accesses
|
|
///
|
|
/// The precise Rust aliasing rules are somewhat in flux, but the main points are not contentious:
|
|
///
|
|
/// - If you create a safe reference with lifetime `'a` (either a `&T` or `&mut T` reference), then
|
|
/// you must not access the data in any way that contradicts that reference for the remainder of
|
|
/// `'a`. For example, this means that if you take the `*mut T` from an `UnsafeCell<T>` and cast it
|
|
/// to an `&T`, then the data in `T` must remain immutable (modulo any `UnsafeCell` data found
|
|
/// within `T`, of course) until that reference's lifetime expires. Similarly, if you create a `&mut
|
|
/// T` reference that is released to safe code, then you must not access the data within the
|
|
/// `UnsafeCell` until that reference expires.
|
|
///
|
|
/// - For both `&T` without `UnsafeCell<_>` and `&mut T`, you must also not deallocate the data
|
|
/// until the reference expires. As a special exception, given an `&T`, any part of it that is
|
|
/// inside an `UnsafeCell<_>` may be deallocated during the lifetime of the reference, after the
|
|
/// last time the reference is used (dereferenced or reborrowed). Since you cannot deallocate a part
|
|
/// of what a reference points to, this means the memory an `&T` points to can be deallocated only if
|
|
/// *every part of it* (including padding) is inside an `UnsafeCell`.
|
|
///
|
|
/// However, whenever a `&UnsafeCell<T>` is constructed or dereferenced, it must still point to
|
|
/// live memory and the compiler is allowed to insert spurious reads if it can prove that this
|
|
/// memory has not yet been deallocated.
|
|
///
|
|
/// To assist with proper design, the following scenarios are explicitly declared legal
|
|
/// for single-threaded code:
|
|
///
|
|
/// 1. A `&T` reference can be released to safe code and there it can co-exist with other `&T`
|
|
/// references, but not with a `&mut T`
|
|
///
|
|
/// 2. A `&mut T` reference may be released to safe code provided neither other `&mut T` nor `&T`
|
|
/// co-exist with it. A `&mut T` must always be unique.
|
|
///
|
|
/// Note that whilst mutating the contents of an `&UnsafeCell<T>` (even while other
|
|
/// `&UnsafeCell<T>` references alias the cell) is
|
|
/// ok (provided you enforce the above invariants some other way), it is still undefined behavior
|
|
/// to have multiple `&mut UnsafeCell<T>` aliases. That is, `UnsafeCell` is a wrapper
|
|
/// designed to have a special interaction with _shared_ accesses (_i.e._, through an
|
|
/// `&UnsafeCell<_>` reference); there is no magic whatsoever when dealing with _exclusive_
|
|
/// accesses (_e.g._, through a `&mut UnsafeCell<_>`): neither the cell nor the wrapped value
|
|
/// may be aliased for the duration of that `&mut` borrow.
|
|
/// This is showcased by the [`.get_mut()`] accessor, which is a _safe_ getter that yields
|
|
/// a `&mut T`.
|
|
///
|
|
/// [`.get_mut()`]: `UnsafeCell::get_mut`
|
|
///
|
|
/// # Memory layout
|
|
///
|
|
/// `UnsafeCell<T>` has the same in-memory representation as its inner type `T`. A consequence
|
|
/// of this guarantee is that it is possible to convert between `T` and `UnsafeCell<T>`.
|
|
/// Special care has to be taken when converting a nested `T` inside of an `Outer<T>` type
|
|
/// to an `Outer<UnsafeCell<T>>` type: this is not sound when the `Outer<T>` type enables [niche]
|
|
/// optimizations. For example, the type `Option<NonNull<u8>>` is typically 8 bytes large on
|
|
/// 64-bit platforms, but the type `Option<UnsafeCell<NonNull<u8>>>` takes up 16 bytes of space.
|
|
/// Therefore this is not a valid conversion, despite `NonNull<u8>` and `UnsafeCell<NonNull<u8>>>`
|
|
/// having the same memory layout. This is because `UnsafeCell` disables niche optimizations in
|
|
/// order to avoid its interior mutability property from spreading from `T` into the `Outer` type,
|
|
/// thus this can cause distortions in the type size in these cases.
|
|
///
|
|
/// Note that the only valid way to obtain a `*mut T` pointer to the contents of a
|
|
/// _shared_ `UnsafeCell<T>` is through [`.get()`] or [`.raw_get()`]. A `&mut T` reference
|
|
/// can be obtained by either dereferencing this pointer or by calling [`.get_mut()`]
|
|
/// on an _exclusive_ `UnsafeCell<T>`. Even though `T` and `UnsafeCell<T>` have the
|
|
/// same memory layout, the following is not allowed and undefined behavior:
|
|
///
|
|
/// ```rust,compile_fail
|
|
/// # use std::cell::UnsafeCell;
|
|
/// unsafe fn not_allowed<T>(ptr: &UnsafeCell<T>) -> &mut T {
|
|
/// let t = ptr as *const UnsafeCell<T> as *mut T;
|
|
/// // This is undefined behavior, because the `*mut T` pointer
|
|
/// // was not obtained through `.get()` nor `.raw_get()`:
|
|
/// unsafe { &mut *t }
|
|
/// }
|
|
/// ```
|
|
///
|
|
/// Instead, do this:
|
|
///
|
|
/// ```rust
|
|
/// # use std::cell::UnsafeCell;
|
|
/// // Safety: the caller must ensure that there are no references that
|
|
/// // point to the *contents* of the `UnsafeCell`.
|
|
/// unsafe fn get_mut<T>(ptr: &UnsafeCell<T>) -> &mut T {
|
|
/// unsafe { &mut *ptr.get() }
|
|
/// }
|
|
/// ```
|
|
///
|
|
/// Converting in the other direction from a `&mut T`
|
|
/// to an `&UnsafeCell<T>` is allowed:
|
|
///
|
|
/// ```rust
|
|
/// # use std::cell::UnsafeCell;
|
|
/// fn get_shared<T>(ptr: &mut T) -> &UnsafeCell<T> {
|
|
/// let t = ptr as *mut T as *const UnsafeCell<T>;
|
|
/// // SAFETY: `T` and `UnsafeCell<T>` have the same memory layout
|
|
/// unsafe { &*t }
|
|
/// }
|
|
/// ```
|
|
///
|
|
/// [niche]: https://rust-lang.github.io/unsafe-code-guidelines/glossary.html#niche
|
|
/// [`.raw_get()`]: `UnsafeCell::raw_get`
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// Here is an example showcasing how to soundly mutate the contents of an `UnsafeCell<_>` despite
|
|
/// there being multiple references aliasing the cell:
|
|
///
|
|
/// ```
|
|
/// use std::cell::UnsafeCell;
|
|
///
|
|
/// let x: UnsafeCell<i32> = 42.into();
|
|
/// // Get multiple / concurrent / shared references to the same `x`.
|
|
/// let (p1, p2): (&UnsafeCell<i32>, &UnsafeCell<i32>) = (&x, &x);
|
|
///
|
|
/// unsafe {
|
|
/// // SAFETY: within this scope there are no other references to `x`'s contents,
|
|
/// // so ours is effectively unique.
|
|
/// let p1_exclusive: &mut i32 = &mut *p1.get(); // -- borrow --+
|
|
/// *p1_exclusive += 27; // |
|
|
/// } // <---------- cannot go beyond this point -------------------+
|
|
///
|
|
/// unsafe {
|
|
/// // SAFETY: within this scope nobody expects to have exclusive access to `x`'s contents,
|
|
/// // so we can have multiple shared accesses concurrently.
|
|
/// let p2_shared: &i32 = &*p2.get();
|
|
/// assert_eq!(*p2_shared, 42 + 27);
|
|
/// let p1_shared: &i32 = &*p1.get();
|
|
/// assert_eq!(*p1_shared, *p2_shared);
|
|
/// }
|
|
/// ```
|
|
///
|
|
/// The following example showcases the fact that exclusive access to an `UnsafeCell<T>`
|
|
/// implies exclusive access to its `T`:
|
|
///
|
|
/// ```rust
|
|
/// #![forbid(unsafe_code)] // with exclusive accesses,
|
|
/// // `UnsafeCell` is a transparent no-op wrapper,
|
|
/// // so no need for `unsafe` here.
|
|
/// use std::cell::UnsafeCell;
|
|
///
|
|
/// let mut x: UnsafeCell<i32> = 42.into();
|
|
///
|
|
/// // Get a compile-time-checked unique reference to `x`.
|
|
/// let p_unique: &mut UnsafeCell<i32> = &mut x;
|
|
/// // With an exclusive reference, we can mutate the contents for free.
|
|
/// *p_unique.get_mut() = 0;
|
|
/// // Or, equivalently:
|
|
/// x = UnsafeCell::new(0);
|
|
///
|
|
/// // When we own the value, we can extract the contents for free.
|
|
/// let contents: i32 = x.into_inner();
|
|
/// assert_eq!(contents, 0);
|
|
/// ```
|
|
#[lang = "unsafe_cell"]
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
|
#[repr(transparent)]
|
|
#[rustc_pub_transparent]
|
|
pub struct UnsafeCell<T: ?Sized> {
|
|
value: T,
|
|
}
|
|
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
|
impl<T: ?Sized> !Sync for UnsafeCell<T> {}
|
|
|
|
impl<T> UnsafeCell<T> {
|
|
/// Constructs a new instance of `UnsafeCell` which will wrap the specified
|
|
/// value.
|
|
///
|
|
/// All access to the inner value through `&UnsafeCell<T>` requires `unsafe` code.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// use std::cell::UnsafeCell;
|
|
///
|
|
/// let uc = UnsafeCell::new(5);
|
|
/// ```
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
|
#[rustc_const_stable(feature = "const_unsafe_cell_new", since = "1.32.0")]
|
|
#[inline(always)]
|
|
pub const fn new(value: T) -> UnsafeCell<T> {
|
|
UnsafeCell { value }
|
|
}
|
|
|
|
/// Unwraps the value, consuming the cell.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// use std::cell::UnsafeCell;
|
|
///
|
|
/// let uc = UnsafeCell::new(5);
|
|
///
|
|
/// let five = uc.into_inner();
|
|
/// ```
|
|
#[inline(always)]
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
|
#[rustc_const_stable(feature = "const_cell_into_inner", since = "1.83.0")]
|
|
#[rustc_allow_const_fn_unstable(const_precise_live_drops)]
|
|
pub const fn into_inner(self) -> T {
|
|
self.value
|
|
}
|
|
|
|
/// Replace the value in this `UnsafeCell` and return the old value.
|
|
///
|
|
/// # Safety
|
|
///
|
|
/// The caller must take care to avoid aliasing and data races.
|
|
///
|
|
/// - It is Undefined Behavior to allow calls to race with
|
|
/// any other access to the wrapped value.
|
|
/// - It is Undefined Behavior to call this while any other
|
|
/// reference(s) to the wrapped value are alive.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// #![feature(unsafe_cell_access)]
|
|
/// use std::cell::UnsafeCell;
|
|
///
|
|
/// let uc = UnsafeCell::new(5);
|
|
///
|
|
/// let old = unsafe { uc.replace(10) };
|
|
/// assert_eq!(old, 5);
|
|
/// ```
|
|
#[inline]
|
|
#[unstable(feature = "unsafe_cell_access", issue = "136327")]
|
|
pub const unsafe fn replace(&self, value: T) -> T {
|
|
// SAFETY: pointer comes from `&self` so naturally satisfies invariants.
|
|
unsafe { ptr::replace(self.get(), value) }
|
|
}
|
|
}
|
|
|
|
impl<T: ?Sized> UnsafeCell<T> {
|
|
/// Converts from `&mut T` to `&mut UnsafeCell<T>`.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// use std::cell::UnsafeCell;
|
|
///
|
|
/// let mut val = 42;
|
|
/// let uc = UnsafeCell::from_mut(&mut val);
|
|
///
|
|
/// *uc.get_mut() -= 1;
|
|
/// assert_eq!(*uc.get_mut(), 41);
|
|
/// ```
|
|
#[inline(always)]
|
|
#[stable(feature = "unsafe_cell_from_mut", since = "1.84.0")]
|
|
#[rustc_const_stable(feature = "unsafe_cell_from_mut", since = "1.84.0")]
|
|
pub const fn from_mut(value: &mut T) -> &mut UnsafeCell<T> {
|
|
// SAFETY: `UnsafeCell<T>` has the same memory layout as `T` due to #[repr(transparent)].
|
|
unsafe { &mut *(value as *mut T as *mut UnsafeCell<T>) }
|
|
}
|
|
|
|
/// Gets a mutable pointer to the wrapped value.
|
|
///
|
|
/// This can be cast to a pointer of any kind.
|
|
/// Ensure that the access is unique (no active references, mutable or not)
|
|
/// when casting to `&mut T`, and ensure that there are no mutations
|
|
/// or mutable aliases going on when casting to `&T`
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// use std::cell::UnsafeCell;
|
|
///
|
|
/// let uc = UnsafeCell::new(5);
|
|
///
|
|
/// let five = uc.get();
|
|
/// ```
|
|
#[inline(always)]
|
|
#[stable(feature = "rust1", since = "1.0.0")]
|
|
#[rustc_const_stable(feature = "const_unsafecell_get", since = "1.32.0")]
|
|
#[rustc_as_ptr]
|
|
#[rustc_never_returns_null_ptr]
|
|
pub const fn get(&self) -> *mut T {
|
|
// We can just cast the pointer from `UnsafeCell<T>` to `T` because of
|
|
// #[repr(transparent)]. This exploits std's special status, there is
|
|
// no guarantee for user code that this will work in future versions of the compiler!
|
|
self as *const UnsafeCell<T> as *const T as *mut T
|
|
}
|
|
|
|
/// Returns a mutable reference to the underlying data.
|
|
///
|
|
/// This call borrows the `UnsafeCell` mutably (at compile-time) which
|
|
/// guarantees that we possess the only reference.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// use std::cell::UnsafeCell;
|
|
///
|
|
/// let mut c = UnsafeCell::new(5);
|
|
/// *c.get_mut() += 1;
|
|
///
|
|
/// assert_eq!(*c.get_mut(), 6);
|
|
/// ```
|
|
#[inline(always)]
|
|
#[stable(feature = "unsafe_cell_get_mut", since = "1.50.0")]
|
|
#[rustc_const_stable(feature = "const_unsafecell_get_mut", since = "1.83.0")]
|
|
pub const fn get_mut(&mut self) -> &mut T {
|
|
&mut self.value
|
|
}
|
|
|
|
/// Gets a mutable pointer to the wrapped value.
|
|
/// The difference from [`get`] is that this function accepts a raw pointer,
|
|
/// which is useful to avoid the creation of temporary references.
|
|
///
|
|
/// The result can be cast to a pointer of any kind.
|
|
/// Ensure that the access is unique (no active references, mutable or not)
|
|
/// when casting to `&mut T`, and ensure that there are no mutations
|
|
/// or mutable aliases going on when casting to `&T`.
|
|
///
|
|
/// [`get`]: UnsafeCell::get()
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// Gradual initialization of an `UnsafeCell` requires `raw_get`, as
|
|
/// calling `get` would require creating a reference to uninitialized data:
|
|
///
|
|
/// ```
|
|
/// use std::cell::UnsafeCell;
|
|
/// use std::mem::MaybeUninit;
|
|
///
|
|
/// let m = MaybeUninit::<UnsafeCell<i32>>::uninit();
|
|
/// unsafe { UnsafeCell::raw_get(m.as_ptr()).write(5); }
|
|
/// // avoid below which references to uninitialized data
|
|
/// // unsafe { UnsafeCell::get(&*m.as_ptr()).write(5); }
|
|
/// let uc = unsafe { m.assume_init() };
|
|
///
|
|
/// assert_eq!(uc.into_inner(), 5);
|
|
/// ```
|
|
#[inline(always)]
|
|
#[stable(feature = "unsafe_cell_raw_get", since = "1.56.0")]
|
|
#[rustc_const_stable(feature = "unsafe_cell_raw_get", since = "1.56.0")]
|
|
#[rustc_diagnostic_item = "unsafe_cell_raw_get"]
|
|
pub const fn raw_get(this: *const Self) -> *mut T {
|
|
// We can just cast the pointer from `UnsafeCell<T>` to `T` because of
|
|
// #[repr(transparent)]. This exploits std's special status, there is
|
|
// no guarantee for user code that this will work in future versions of the compiler!
|
|
this as *const T as *mut T
|
|
}
|
|
|
|
/// Get a shared reference to the value within the `UnsafeCell`.
|
|
///
|
|
/// # Safety
|
|
///
|
|
/// - It is Undefined Behavior to call this while any mutable
|
|
/// reference to the wrapped value is alive.
|
|
/// - Mutating the wrapped value while the returned
|
|
/// reference is alive is Undefined Behavior.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// #![feature(unsafe_cell_access)]
|
|
/// use std::cell::UnsafeCell;
|
|
///
|
|
/// let uc = UnsafeCell::new(5);
|
|
///
|
|
/// let val = unsafe { uc.as_ref_unchecked() };
|
|
/// assert_eq!(val, &5);
|
|
/// ```
|
|
#[inline]
|
|
#[unstable(feature = "unsafe_cell_access", issue = "136327")]
|
|
pub const unsafe fn as_ref_unchecked(&self) -> &T {
|
|
// SAFETY: pointer comes from `&self` so naturally satisfies ptr-to-ref invariants.
|
|
unsafe { self.get().as_ref_unchecked() }
|
|
}
|
|
|
|
/// Get an exclusive reference to the value within the `UnsafeCell`.
|
|
///
|
|
/// # Safety
|
|
///
|
|
/// - It is Undefined Behavior to call this while any other
|
|
/// reference(s) to the wrapped value are alive.
|
|
/// - Mutating the wrapped value through other means while the
|
|
/// returned reference is alive is Undefined Behavior.
|
|
///
|
|
/// # Examples
|
|
///
|
|
/// ```
|
|
/// #![feature(unsafe_cell_access)]
|
|
/// use std::cell::UnsafeCell;
|
|
///
|
|
/// let uc = UnsafeCell::new(5);
|
|
///
|
|
/// unsafe { *uc.as_mut_unchecked() += 1; }
|
|
/// assert_eq!(uc.into_inner(), 6);
|
|
/// ```
|
|
#[inline]
|
|
#[unstable(feature = "unsafe_cell_access", issue = "136327")]
|
|
#[allow(clippy::mut_from_ref)]
|
|
pub const unsafe fn as_mut_unchecked(&self) -> &mut T {
|
|
// SAFETY: pointer comes from `&self` so naturally satisfies ptr-to-ref invariants.
|
|
unsafe { self.get().as_mut_unchecked() }
|
|
}
|
|
}
|
|
|
|
#[stable(feature = "unsafe_cell_default", since = "1.10.0")]
|
|
impl<T: Default> Default for UnsafeCell<T> {
|
|
/// Creates an `UnsafeCell`, with the `Default` value for T.
|
|
fn default() -> UnsafeCell<T> {
|
|
UnsafeCell::new(Default::default())
|
|
}
|
|
}
|
|
|
|
#[stable(feature = "cell_from", since = "1.12.0")]
|
|
impl<T> From<T> for UnsafeCell<T> {
|
|
/// Creates a new `UnsafeCell<T>` containing the given value.
|
|
fn from(t: T) -> UnsafeCell<T> {
|
|
UnsafeCell::new(t)
|
|
}
|
|
}
|
|
|
|
#[unstable(feature = "coerce_unsized", issue = "18598")]
|
|
impl<T: CoerceUnsized<U>, U> CoerceUnsized<UnsafeCell<U>> for UnsafeCell<T> {}
|
|
|
|
// Allow types that wrap `UnsafeCell` to also implement `DispatchFromDyn`
|
|
// and become dyn-compatible method receivers.
|
|
// Note that currently `UnsafeCell` itself cannot be a method receiver
|
|
// because it does not implement Deref.
|
|
// In other words:
|
|
// `self: UnsafeCell<&Self>` won't work
|
|
// `self: UnsafeCellWrapper<Self>` becomes possible
|
|
#[unstable(feature = "dispatch_from_dyn", issue = "none")]
|
|
impl<T: DispatchFromDyn<U>, U> DispatchFromDyn<UnsafeCell<U>> for UnsafeCell<T> {}
|
|
|
|
#[unstable(feature = "pointer_like_trait", issue = "none")]
|
|
impl<T: PointerLike> PointerLike for UnsafeCell<T> {}
|
|
|
|
/// [`UnsafeCell`], but [`Sync`].
|
|
///
|
|
/// This is just an `UnsafeCell`, except it implements `Sync`
|
|
/// if `T` implements `Sync`.
|
|
///
|
|
/// `UnsafeCell` doesn't implement `Sync`, to prevent accidental mis-use.
|
|
/// You can use `SyncUnsafeCell` instead of `UnsafeCell` to allow it to be
|
|
/// shared between threads, if that's intentional.
|
|
/// Providing proper synchronization is still the task of the user,
|
|
/// making this type just as unsafe to use.
|
|
///
|
|
/// See [`UnsafeCell`] for details.
|
|
#[unstable(feature = "sync_unsafe_cell", issue = "95439")]
|
|
#[repr(transparent)]
|
|
#[rustc_diagnostic_item = "SyncUnsafeCell"]
|
|
#[rustc_pub_transparent]
|
|
pub struct SyncUnsafeCell<T: ?Sized> {
|
|
value: UnsafeCell<T>,
|
|
}
|
|
|
|
#[unstable(feature = "sync_unsafe_cell", issue = "95439")]
|
|
unsafe impl<T: ?Sized + Sync> Sync for SyncUnsafeCell<T> {}
|
|
|
|
#[unstable(feature = "sync_unsafe_cell", issue = "95439")]
|
|
impl<T> SyncUnsafeCell<T> {
|
|
/// Constructs a new instance of `SyncUnsafeCell` which will wrap the specified value.
|
|
#[inline]
|
|
pub const fn new(value: T) -> Self {
|
|
Self { value: UnsafeCell { value } }
|
|
}
|
|
|
|
/// Unwraps the value, consuming the cell.
|
|
#[inline]
|
|
#[rustc_const_unstable(feature = "sync_unsafe_cell", issue = "95439")]
|
|
pub const fn into_inner(self) -> T {
|
|
self.value.into_inner()
|
|
}
|
|
}
|
|
|
|
#[unstable(feature = "sync_unsafe_cell", issue = "95439")]
|
|
impl<T: ?Sized> SyncUnsafeCell<T> {
|
|
/// Gets a mutable pointer to the wrapped value.
|
|
///
|
|
/// This can be cast to a pointer of any kind.
|
|
/// Ensure that the access is unique (no active references, mutable or not)
|
|
/// when casting to `&mut T`, and ensure that there are no mutations
|
|
/// or mutable aliases going on when casting to `&T`
|
|
#[inline]
|
|
#[rustc_as_ptr]
|
|
#[rustc_never_returns_null_ptr]
|
|
pub const fn get(&self) -> *mut T {
|
|
self.value.get()
|
|
}
|
|
|
|
/// Returns a mutable reference to the underlying data.
|
|
///
|
|
/// This call borrows the `SyncUnsafeCell` mutably (at compile-time) which
|
|
/// guarantees that we possess the only reference.
|
|
#[inline]
|
|
pub const fn get_mut(&mut self) -> &mut T {
|
|
self.value.get_mut()
|
|
}
|
|
|
|
/// Gets a mutable pointer to the wrapped value.
|
|
///
|
|
/// See [`UnsafeCell::get`] for details.
|
|
#[inline]
|
|
pub const fn raw_get(this: *const Self) -> *mut T {
|
|
// We can just cast the pointer from `SyncUnsafeCell<T>` to `T` because
|
|
// of #[repr(transparent)] on both SyncUnsafeCell and UnsafeCell.
|
|
// See UnsafeCell::raw_get.
|
|
this as *const T as *mut T
|
|
}
|
|
}
|
|
|
|
#[unstable(feature = "sync_unsafe_cell", issue = "95439")]
|
|
impl<T: Default> Default for SyncUnsafeCell<T> {
|
|
/// Creates an `SyncUnsafeCell`, with the `Default` value for T.
|
|
fn default() -> SyncUnsafeCell<T> {
|
|
SyncUnsafeCell::new(Default::default())
|
|
}
|
|
}
|
|
|
|
#[unstable(feature = "sync_unsafe_cell", issue = "95439")]
|
|
impl<T> From<T> for SyncUnsafeCell<T> {
|
|
/// Creates a new `SyncUnsafeCell<T>` containing the given value.
|
|
fn from(t: T) -> SyncUnsafeCell<T> {
|
|
SyncUnsafeCell::new(t)
|
|
}
|
|
}
|
|
|
|
#[unstable(feature = "coerce_unsized", issue = "18598")]
|
|
//#[unstable(feature = "sync_unsafe_cell", issue = "95439")]
|
|
impl<T: CoerceUnsized<U>, U> CoerceUnsized<SyncUnsafeCell<U>> for SyncUnsafeCell<T> {}
|
|
|
|
// Allow types that wrap `SyncUnsafeCell` to also implement `DispatchFromDyn`
|
|
// and become dyn-compatible method receivers.
|
|
// Note that currently `SyncUnsafeCell` itself cannot be a method receiver
|
|
// because it does not implement Deref.
|
|
// In other words:
|
|
// `self: SyncUnsafeCell<&Self>` won't work
|
|
// `self: SyncUnsafeCellWrapper<Self>` becomes possible
|
|
#[unstable(feature = "dispatch_from_dyn", issue = "none")]
|
|
//#[unstable(feature = "sync_unsafe_cell", issue = "95439")]
|
|
impl<T: DispatchFromDyn<U>, U> DispatchFromDyn<SyncUnsafeCell<U>> for SyncUnsafeCell<T> {}
|
|
|
|
#[unstable(feature = "pointer_like_trait", issue = "none")]
|
|
impl<T: PointerLike> PointerLike for SyncUnsafeCell<T> {}
|
|
|
|
#[allow(unused)]
|
|
fn assert_coerce_unsized(
|
|
a: UnsafeCell<&i32>,
|
|
b: SyncUnsafeCell<&i32>,
|
|
c: Cell<&i32>,
|
|
d: RefCell<&i32>,
|
|
) {
|
|
let _: UnsafeCell<&dyn Send> = a;
|
|
let _: SyncUnsafeCell<&dyn Send> = b;
|
|
let _: Cell<&dyn Send> = c;
|
|
let _: RefCell<&dyn Send> = d;
|
|
}
|
|
|
|
#[unstable(feature = "pin_coerce_unsized_trait", issue = "123430")]
|
|
unsafe impl<T: ?Sized> PinCoerceUnsized for UnsafeCell<T> {}
|
|
|
|
#[unstable(feature = "pin_coerce_unsized_trait", issue = "123430")]
|
|
unsafe impl<T: ?Sized> PinCoerceUnsized for SyncUnsafeCell<T> {}
|
|
|
|
#[unstable(feature = "pin_coerce_unsized_trait", issue = "123430")]
|
|
unsafe impl<T: ?Sized> PinCoerceUnsized for Cell<T> {}
|
|
|
|
#[unstable(feature = "pin_coerce_unsized_trait", issue = "123430")]
|
|
unsafe impl<T: ?Sized> PinCoerceUnsized for RefCell<T> {}
|
|
|
|
#[unstable(feature = "pin_coerce_unsized_trait", issue = "123430")]
|
|
unsafe impl<'b, T: ?Sized> PinCoerceUnsized for Ref<'b, T> {}
|
|
|
|
#[unstable(feature = "pin_coerce_unsized_trait", issue = "123430")]
|
|
unsafe impl<'b, T: ?Sized> PinCoerceUnsized for RefMut<'b, T> {}
|