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b38106b6d8
`rustc_data_structures::thin_vec::ThinVec` looks like this: ``` pub struct ThinVec<T>(Option<Box<Vec<T>>>); ``` It's just a zero word if the vector is empty, but requires two allocations if it is non-empty. So it's only usable in cases where the vector is empty most of the time. This commit removes it in favour of `thin_vec::ThinVec`, which is also word-sized, but stores the length and capacity in the same allocation as the elements. It's good in a wider variety of situation, e.g. in enum variants where the vector is usually/always non-empty. The commit also: - Sorts some `Cargo.toml` dependency lists, to make additions easier. - Sorts some `use` item lists, to make additions easier. - Changes `clean_trait_ref_with_bindings` to take a `ThinVec<TypeBinding>` rather than a `&[TypeBinding]`, because this avoid some unnecessary allocations.
80 lines
2.4 KiB
Rust
80 lines
2.4 KiB
Rust
use smallvec::{Array, SmallVec};
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use std::ptr;
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use thin_vec::ThinVec;
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pub trait MapInPlace<T>: Sized {
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fn map_in_place<F>(&mut self, mut f: F)
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where
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F: FnMut(T) -> T,
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{
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self.flat_map_in_place(|e| Some(f(e)))
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}
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fn flat_map_in_place<F, I>(&mut self, f: F)
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where
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F: FnMut(T) -> I,
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I: IntoIterator<Item = T>;
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}
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// The implementation of this method is syntactically identical for all the
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// different vector types.
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macro_rules! flat_map_in_place {
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() => {
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fn flat_map_in_place<F, I>(&mut self, mut f: F)
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where
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F: FnMut(T) -> I,
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I: IntoIterator<Item = T>,
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{
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let mut read_i = 0;
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let mut write_i = 0;
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unsafe {
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let mut old_len = self.len();
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self.set_len(0); // make sure we just leak elements in case of panic
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while read_i < old_len {
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// move the read_i'th item out of the vector and map it
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// to an iterator
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let e = ptr::read(self.as_ptr().add(read_i));
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let iter = f(e).into_iter();
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read_i += 1;
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for e in iter {
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if write_i < read_i {
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ptr::write(self.as_mut_ptr().add(write_i), e);
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write_i += 1;
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} else {
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// If this is reached we ran out of space
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// in the middle of the vector.
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// However, the vector is in a valid state here,
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// so we just do a somewhat inefficient insert.
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self.set_len(old_len);
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self.insert(write_i, e);
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old_len = self.len();
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self.set_len(0);
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read_i += 1;
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write_i += 1;
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}
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}
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}
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// write_i tracks the number of actually written new items.
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self.set_len(write_i);
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}
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}
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};
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}
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impl<T> MapInPlace<T> for Vec<T> {
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flat_map_in_place!();
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}
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impl<T, A: Array<Item = T>> MapInPlace<T> for SmallVec<A> {
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flat_map_in_place!();
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}
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impl<T> MapInPlace<T> for ThinVec<T> {
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flat_map_in_place!();
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}
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