mirror of
https://github.com/rust-lang/rust.git
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a8c669461f
The ASCII subset of Unicode is fixed and will never change, so we don't need to generate tables for it with every new Unicode version. This saves a few bytes of static data and speeds up `char::is_control` and `char::is_grapheme_extended` on ASCII inputs. Since the table lookup functions exported from the `unicode` module will give nonsensical errors on ASCII input (and in fact will panic in debug mode), I had to add some private wrapper methods to `char` which check for ASCII-ness first.
714 lines
25 KiB
Rust
714 lines
25 KiB
Rust
//! Utilities for the `str` primitive type.
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//!
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//! *[See also the `str` primitive type](str).*
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#![stable(feature = "rust1", since = "1.0.0")]
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// Many of the usings in this module are only used in the test configuration.
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// It's cleaner to just turn off the unused_imports warning than to fix them.
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#![allow(unused_imports)]
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use core::borrow::{Borrow, BorrowMut};
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use core::iter::FusedIterator;
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use core::mem::MaybeUninit;
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#[stable(feature = "encode_utf16", since = "1.8.0")]
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pub use core::str::EncodeUtf16;
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#[stable(feature = "split_ascii_whitespace", since = "1.34.0")]
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pub use core::str::SplitAsciiWhitespace;
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#[stable(feature = "split_inclusive", since = "1.51.0")]
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pub use core::str::SplitInclusive;
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#[stable(feature = "rust1", since = "1.0.0")]
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pub use core::str::SplitWhitespace;
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#[stable(feature = "rust1", since = "1.0.0")]
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pub use core::str::pattern;
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use core::str::pattern::{DoubleEndedSearcher, Pattern, ReverseSearcher, Searcher, Utf8Pattern};
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#[stable(feature = "rust1", since = "1.0.0")]
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pub use core::str::{Bytes, CharIndices, Chars, from_utf8, from_utf8_mut};
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#[stable(feature = "str_escape", since = "1.34.0")]
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pub use core::str::{EscapeDebug, EscapeDefault, EscapeUnicode};
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#[stable(feature = "rust1", since = "1.0.0")]
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pub use core::str::{FromStr, Utf8Error};
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#[allow(deprecated)]
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#[stable(feature = "rust1", since = "1.0.0")]
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pub use core::str::{Lines, LinesAny};
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#[stable(feature = "rust1", since = "1.0.0")]
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pub use core::str::{MatchIndices, RMatchIndices};
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#[stable(feature = "rust1", since = "1.0.0")]
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pub use core::str::{Matches, RMatches};
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#[stable(feature = "rust1", since = "1.0.0")]
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pub use core::str::{ParseBoolError, from_utf8_unchecked, from_utf8_unchecked_mut};
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#[stable(feature = "rust1", since = "1.0.0")]
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pub use core::str::{RSplit, Split};
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#[stable(feature = "rust1", since = "1.0.0")]
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pub use core::str::{RSplitN, SplitN};
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#[stable(feature = "rust1", since = "1.0.0")]
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pub use core::str::{RSplitTerminator, SplitTerminator};
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#[stable(feature = "utf8_chunks", since = "1.79.0")]
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pub use core::str::{Utf8Chunk, Utf8Chunks};
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#[unstable(feature = "str_from_raw_parts", issue = "119206")]
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pub use core::str::{from_raw_parts, from_raw_parts_mut};
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use core::unicode::conversions;
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use core::{mem, ptr};
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use crate::borrow::ToOwned;
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use crate::boxed::Box;
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use crate::slice::{Concat, Join, SliceIndex};
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use crate::string::String;
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use crate::vec::Vec;
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/// Note: `str` in `Concat<str>` is not meaningful here.
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/// This type parameter of the trait only exists to enable another impl.
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#[cfg(not(no_global_oom_handling))]
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#[unstable(feature = "slice_concat_ext", issue = "27747")]
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impl<S: Borrow<str>> Concat<str> for [S] {
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type Output = String;
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fn concat(slice: &Self) -> String {
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Join::join(slice, "")
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}
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}
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#[cfg(not(no_global_oom_handling))]
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#[unstable(feature = "slice_concat_ext", issue = "27747")]
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impl<S: Borrow<str>> Join<&str> for [S] {
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type Output = String;
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fn join(slice: &Self, sep: &str) -> String {
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unsafe { String::from_utf8_unchecked(join_generic_copy(slice, sep.as_bytes())) }
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}
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}
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#[cfg(not(no_global_oom_handling))]
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macro_rules! specialize_for_lengths {
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($separator:expr, $target:expr, $iter:expr; $($num:expr),*) => {{
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let mut target = $target;
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let iter = $iter;
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let sep_bytes = $separator;
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match $separator.len() {
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$(
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// loops with hardcoded sizes run much faster
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// specialize the cases with small separator lengths
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$num => {
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for s in iter {
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copy_slice_and_advance!(target, sep_bytes);
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let content_bytes = s.borrow().as_ref();
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copy_slice_and_advance!(target, content_bytes);
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}
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},
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)*
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_ => {
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// arbitrary non-zero size fallback
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for s in iter {
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copy_slice_and_advance!(target, sep_bytes);
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let content_bytes = s.borrow().as_ref();
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copy_slice_and_advance!(target, content_bytes);
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}
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}
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}
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target
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}}
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}
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#[cfg(not(no_global_oom_handling))]
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macro_rules! copy_slice_and_advance {
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($target:expr, $bytes:expr) => {
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let len = $bytes.len();
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let (head, tail) = { $target }.split_at_mut(len);
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head.copy_from_slice($bytes);
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$target = tail;
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};
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}
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// Optimized join implementation that works for both Vec<T> (T: Copy) and String's inner vec
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// Currently (2018-05-13) there is a bug with type inference and specialization (see issue #36262)
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// For this reason SliceConcat<T> is not specialized for T: Copy and SliceConcat<str> is the
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// only user of this function. It is left in place for the time when that is fixed.
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//
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// the bounds for String-join are S: Borrow<str> and for Vec-join Borrow<[T]>
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// [T] and str both impl AsRef<[T]> for some T
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// => s.borrow().as_ref() and we always have slices
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#[cfg(not(no_global_oom_handling))]
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fn join_generic_copy<B, T, S>(slice: &[S], sep: &[T]) -> Vec<T>
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where
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T: Copy,
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B: AsRef<[T]> + ?Sized,
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S: Borrow<B>,
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{
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let sep_len = sep.len();
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let mut iter = slice.iter();
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// the first slice is the only one without a separator preceding it
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let first = match iter.next() {
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Some(first) => first,
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None => return vec![],
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};
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// compute the exact total length of the joined Vec
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// if the `len` calculation overflows, we'll panic
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// we would have run out of memory anyway and the rest of the function requires
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// the entire Vec pre-allocated for safety
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let reserved_len = sep_len
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.checked_mul(iter.len())
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.and_then(|n| {
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slice.iter().map(|s| s.borrow().as_ref().len()).try_fold(n, usize::checked_add)
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})
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.expect("attempt to join into collection with len > usize::MAX");
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// prepare an uninitialized buffer
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let mut result = Vec::with_capacity(reserved_len);
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debug_assert!(result.capacity() >= reserved_len);
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result.extend_from_slice(first.borrow().as_ref());
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unsafe {
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let pos = result.len();
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let target = result.spare_capacity_mut().get_unchecked_mut(..reserved_len - pos);
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// Convert the separator and slices to slices of MaybeUninit
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// to simplify implementation in specialize_for_lengths
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let sep_uninit = core::slice::from_raw_parts(sep.as_ptr().cast(), sep.len());
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let iter_uninit = iter.map(|it| {
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let it = it.borrow().as_ref();
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core::slice::from_raw_parts(it.as_ptr().cast(), it.len())
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});
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// copy separator and slices over without bounds checks
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// generate loops with hardcoded offsets for small separators
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// massive improvements possible (~ x2)
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let remain = specialize_for_lengths!(sep_uninit, target, iter_uninit; 0, 1, 2, 3, 4);
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// A weird borrow implementation may return different
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// slices for the length calculation and the actual copy.
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// Make sure we don't expose uninitialized bytes to the caller.
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let result_len = reserved_len - remain.len();
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result.set_len(result_len);
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}
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result
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}
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#[stable(feature = "rust1", since = "1.0.0")]
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impl Borrow<str> for String {
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#[inline]
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fn borrow(&self) -> &str {
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&self[..]
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}
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}
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#[stable(feature = "string_borrow_mut", since = "1.36.0")]
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impl BorrowMut<str> for String {
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#[inline]
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fn borrow_mut(&mut self) -> &mut str {
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&mut self[..]
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}
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}
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#[cfg(not(no_global_oom_handling))]
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#[stable(feature = "rust1", since = "1.0.0")]
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impl ToOwned for str {
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type Owned = String;
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#[inline]
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fn to_owned(&self) -> String {
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unsafe { String::from_utf8_unchecked(self.as_bytes().to_owned()) }
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}
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#[inline]
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fn clone_into(&self, target: &mut String) {
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target.clear();
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target.push_str(self);
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}
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}
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/// Methods for string slices.
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impl str {
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/// Converts a `Box<str>` into a `Box<[u8]>` without copying or allocating.
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///
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/// # Examples
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///
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/// ```
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/// let s = "this is a string";
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/// let boxed_str = s.to_owned().into_boxed_str();
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/// let boxed_bytes = boxed_str.into_boxed_bytes();
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/// assert_eq!(*boxed_bytes, *s.as_bytes());
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/// ```
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#[rustc_allow_incoherent_impl]
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#[stable(feature = "str_box_extras", since = "1.20.0")]
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#[must_use = "`self` will be dropped if the result is not used"]
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#[inline]
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pub fn into_boxed_bytes(self: Box<Self>) -> Box<[u8]> {
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self.into()
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}
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/// Replaces all matches of a pattern with another string.
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///
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/// `replace` creates a new [`String`], and copies the data from this string slice into it.
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/// While doing so, it attempts to find matches of a pattern. If it finds any, it
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/// replaces them with the replacement string slice.
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///
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/// # Examples
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///
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/// ```
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/// let s = "this is old";
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///
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/// assert_eq!("this is new", s.replace("old", "new"));
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/// assert_eq!("than an old", s.replace("is", "an"));
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/// ```
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///
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/// When the pattern doesn't match, it returns this string slice as [`String`]:
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///
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/// ```
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/// let s = "this is old";
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/// assert_eq!(s, s.replace("cookie monster", "little lamb"));
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/// ```
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#[cfg(not(no_global_oom_handling))]
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#[rustc_allow_incoherent_impl]
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#[must_use = "this returns the replaced string as a new allocation, \
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without modifying the original"]
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#[stable(feature = "rust1", since = "1.0.0")]
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#[inline]
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pub fn replace<P: Pattern>(&self, from: P, to: &str) -> String {
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// Fast path for replacing a single ASCII character with another.
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if let Some(from_byte) = match from.as_utf8_pattern() {
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Some(Utf8Pattern::StringPattern([from_byte])) => Some(*from_byte),
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Some(Utf8Pattern::CharPattern(c)) => c.as_ascii().map(|ascii_char| ascii_char.to_u8()),
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_ => None,
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} {
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if let [to_byte] = to.as_bytes() {
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return unsafe { replace_ascii(self.as_bytes(), from_byte, *to_byte) };
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}
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}
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// Set result capacity to self.len() when from.len() <= to.len()
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let default_capacity = match from.as_utf8_pattern() {
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Some(Utf8Pattern::StringPattern(s)) if s.len() <= to.len() => self.len(),
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Some(Utf8Pattern::CharPattern(c)) if c.len_utf8() <= to.len() => self.len(),
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_ => 0,
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};
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let mut result = String::with_capacity(default_capacity);
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let mut last_end = 0;
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for (start, part) in self.match_indices(from) {
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result.push_str(unsafe { self.get_unchecked(last_end..start) });
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result.push_str(to);
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last_end = start + part.len();
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}
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result.push_str(unsafe { self.get_unchecked(last_end..self.len()) });
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result
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}
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/// Replaces first N matches of a pattern with another string.
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///
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/// `replacen` creates a new [`String`], and copies the data from this string slice into it.
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/// While doing so, it attempts to find matches of a pattern. If it finds any, it
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/// replaces them with the replacement string slice at most `count` times.
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///
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/// # Examples
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///
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/// ```
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/// let s = "foo foo 123 foo";
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/// assert_eq!("new new 123 foo", s.replacen("foo", "new", 2));
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/// assert_eq!("faa fao 123 foo", s.replacen('o', "a", 3));
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/// assert_eq!("foo foo new23 foo", s.replacen(char::is_numeric, "new", 1));
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/// ```
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///
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/// When the pattern doesn't match, it returns this string slice as [`String`]:
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///
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/// ```
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/// let s = "this is old";
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/// assert_eq!(s, s.replacen("cookie monster", "little lamb", 10));
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/// ```
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#[cfg(not(no_global_oom_handling))]
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#[rustc_allow_incoherent_impl]
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#[doc(alias = "replace_first")]
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#[must_use = "this returns the replaced string as a new allocation, \
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without modifying the original"]
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#[stable(feature = "str_replacen", since = "1.16.0")]
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pub fn replacen<P: Pattern>(&self, pat: P, to: &str, count: usize) -> String {
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// Hope to reduce the times of re-allocation
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let mut result = String::with_capacity(32);
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let mut last_end = 0;
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for (start, part) in self.match_indices(pat).take(count) {
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result.push_str(unsafe { self.get_unchecked(last_end..start) });
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result.push_str(to);
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last_end = start + part.len();
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}
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result.push_str(unsafe { self.get_unchecked(last_end..self.len()) });
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result
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}
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/// Returns the lowercase equivalent of this string slice, as a new [`String`].
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///
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/// 'Lowercase' is defined according to the terms of the Unicode Derived Core Property
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/// `Lowercase`.
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///
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/// Since some characters can expand into multiple characters when changing
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/// the case, this function returns a [`String`] instead of modifying the
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/// parameter in-place.
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///
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/// # Examples
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///
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/// Basic usage:
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///
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/// ```
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/// let s = "HELLO";
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///
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/// assert_eq!("hello", s.to_lowercase());
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/// ```
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///
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/// A tricky example, with sigma:
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///
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/// ```
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/// let sigma = "Σ";
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///
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/// assert_eq!("σ", sigma.to_lowercase());
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///
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/// // but at the end of a word, it's ς, not σ:
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/// let odysseus = "ὈΔΥΣΣΕΎΣ";
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///
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/// assert_eq!("ὀδυσσεύς", odysseus.to_lowercase());
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/// ```
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///
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/// Languages without case are not changed:
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///
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/// ```
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/// let new_year = "农历新年";
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///
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/// assert_eq!(new_year, new_year.to_lowercase());
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/// ```
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#[cfg(not(no_global_oom_handling))]
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#[rustc_allow_incoherent_impl]
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#[must_use = "this returns the lowercase string as a new String, \
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without modifying the original"]
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#[stable(feature = "unicode_case_mapping", since = "1.2.0")]
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pub fn to_lowercase(&self) -> String {
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let (mut s, rest) = convert_while_ascii(self, u8::to_ascii_lowercase);
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let prefix_len = s.len();
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for (i, c) in rest.char_indices() {
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if c == 'Σ' {
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// Σ maps to σ, except at the end of a word where it maps to ς.
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// This is the only conditional (contextual) but language-independent mapping
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// in `SpecialCasing.txt`,
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// so hard-code it rather than have a generic "condition" mechanism.
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// See https://github.com/rust-lang/rust/issues/26035
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let sigma_lowercase = map_uppercase_sigma(self, prefix_len + i);
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s.push(sigma_lowercase);
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} else {
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match conversions::to_lower(c) {
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[a, '\0', _] => s.push(a),
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[a, b, '\0'] => {
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s.push(a);
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s.push(b);
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}
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[a, b, c] => {
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s.push(a);
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s.push(b);
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s.push(c);
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}
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}
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}
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}
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return s;
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fn map_uppercase_sigma(from: &str, i: usize) -> char {
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// See https://www.unicode.org/versions/Unicode7.0.0/ch03.pdf#G33992
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// for the definition of `Final_Sigma`.
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debug_assert!('Σ'.len_utf8() == 2);
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let is_word_final = case_ignorable_then_cased(from[..i].chars().rev())
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&& !case_ignorable_then_cased(from[i + 2..].chars());
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if is_word_final { 'ς' } else { 'σ' }
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}
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fn case_ignorable_then_cased<I: Iterator<Item = char>>(iter: I) -> bool {
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match iter.skip_while(|&c| c.is_case_ignorable()).next() {
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Some(c) => c.is_cased(),
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None => false,
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}
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}
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}
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/// Returns the uppercase equivalent of this string slice, as a new [`String`].
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///
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/// 'Uppercase' is defined according to the terms of the Unicode Derived Core Property
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/// `Uppercase`.
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///
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/// Since some characters can expand into multiple characters when changing
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/// the case, this function returns a [`String`] instead of modifying the
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/// parameter in-place.
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///
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/// # Examples
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///
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/// Basic usage:
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///
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/// ```
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/// let s = "hello";
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///
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/// assert_eq!("HELLO", s.to_uppercase());
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/// ```
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///
|
||
/// Scripts without case are not changed:
|
||
///
|
||
/// ```
|
||
/// let new_year = "农历新年";
|
||
///
|
||
/// assert_eq!(new_year, new_year.to_uppercase());
|
||
/// ```
|
||
///
|
||
/// One character can become multiple:
|
||
/// ```
|
||
/// let s = "tschüß";
|
||
///
|
||
/// assert_eq!("TSCHÜSS", s.to_uppercase());
|
||
/// ```
|
||
#[cfg(not(no_global_oom_handling))]
|
||
#[rustc_allow_incoherent_impl]
|
||
#[must_use = "this returns the uppercase string as a new String, \
|
||
without modifying the original"]
|
||
#[stable(feature = "unicode_case_mapping", since = "1.2.0")]
|
||
pub fn to_uppercase(&self) -> String {
|
||
let (mut s, rest) = convert_while_ascii(self, u8::to_ascii_uppercase);
|
||
|
||
for c in rest.chars() {
|
||
match conversions::to_upper(c) {
|
||
[a, '\0', _] => s.push(a),
|
||
[a, b, '\0'] => {
|
||
s.push(a);
|
||
s.push(b);
|
||
}
|
||
[a, b, c] => {
|
||
s.push(a);
|
||
s.push(b);
|
||
s.push(c);
|
||
}
|
||
}
|
||
}
|
||
s
|
||
}
|
||
|
||
/// Converts a [`Box<str>`] into a [`String`] without copying or allocating.
|
||
///
|
||
/// # Examples
|
||
///
|
||
/// ```
|
||
/// let string = String::from("birthday gift");
|
||
/// let boxed_str = string.clone().into_boxed_str();
|
||
///
|
||
/// assert_eq!(boxed_str.into_string(), string);
|
||
/// ```
|
||
#[stable(feature = "box_str", since = "1.4.0")]
|
||
#[rustc_allow_incoherent_impl]
|
||
#[must_use = "`self` will be dropped if the result is not used"]
|
||
#[inline]
|
||
pub fn into_string(self: Box<Self>) -> String {
|
||
let slice = Box::<[u8]>::from(self);
|
||
unsafe { String::from_utf8_unchecked(slice.into_vec()) }
|
||
}
|
||
|
||
/// Creates a new [`String`] by repeating a string `n` times.
|
||
///
|
||
/// # Panics
|
||
///
|
||
/// This function will panic if the capacity would overflow.
|
||
///
|
||
/// # Examples
|
||
///
|
||
/// Basic usage:
|
||
///
|
||
/// ```
|
||
/// assert_eq!("abc".repeat(4), String::from("abcabcabcabc"));
|
||
/// ```
|
||
///
|
||
/// A panic upon overflow:
|
||
///
|
||
/// ```should_panic
|
||
/// // this will panic at runtime
|
||
/// let huge = "0123456789abcdef".repeat(usize::MAX);
|
||
/// ```
|
||
#[cfg(not(no_global_oom_handling))]
|
||
#[rustc_allow_incoherent_impl]
|
||
#[must_use]
|
||
#[stable(feature = "repeat_str", since = "1.16.0")]
|
||
#[inline]
|
||
pub fn repeat(&self, n: usize) -> String {
|
||
unsafe { String::from_utf8_unchecked(self.as_bytes().repeat(n)) }
|
||
}
|
||
|
||
/// Returns a copy of this string where each character is mapped to its
|
||
/// ASCII upper case equivalent.
|
||
///
|
||
/// ASCII letters 'a' to 'z' are mapped to 'A' to 'Z',
|
||
/// but non-ASCII letters are unchanged.
|
||
///
|
||
/// To uppercase the value in-place, use [`make_ascii_uppercase`].
|
||
///
|
||
/// To uppercase ASCII characters in addition to non-ASCII characters, use
|
||
/// [`to_uppercase`].
|
||
///
|
||
/// # Examples
|
||
///
|
||
/// ```
|
||
/// let s = "Grüße, Jürgen ❤";
|
||
///
|
||
/// assert_eq!("GRüßE, JüRGEN ❤", s.to_ascii_uppercase());
|
||
/// ```
|
||
///
|
||
/// [`make_ascii_uppercase`]: str::make_ascii_uppercase
|
||
/// [`to_uppercase`]: #method.to_uppercase
|
||
#[cfg(not(no_global_oom_handling))]
|
||
#[rustc_allow_incoherent_impl]
|
||
#[must_use = "to uppercase the value in-place, use `make_ascii_uppercase()`"]
|
||
#[stable(feature = "ascii_methods_on_intrinsics", since = "1.23.0")]
|
||
#[inline]
|
||
pub fn to_ascii_uppercase(&self) -> String {
|
||
let mut s = self.to_owned();
|
||
s.make_ascii_uppercase();
|
||
s
|
||
}
|
||
|
||
/// Returns a copy of this string where each character is mapped to its
|
||
/// ASCII lower case equivalent.
|
||
///
|
||
/// ASCII letters 'A' to 'Z' are mapped to 'a' to 'z',
|
||
/// but non-ASCII letters are unchanged.
|
||
///
|
||
/// To lowercase the value in-place, use [`make_ascii_lowercase`].
|
||
///
|
||
/// To lowercase ASCII characters in addition to non-ASCII characters, use
|
||
/// [`to_lowercase`].
|
||
///
|
||
/// # Examples
|
||
///
|
||
/// ```
|
||
/// let s = "Grüße, Jürgen ❤";
|
||
///
|
||
/// assert_eq!("grüße, jürgen ❤", s.to_ascii_lowercase());
|
||
/// ```
|
||
///
|
||
/// [`make_ascii_lowercase`]: str::make_ascii_lowercase
|
||
/// [`to_lowercase`]: #method.to_lowercase
|
||
#[cfg(not(no_global_oom_handling))]
|
||
#[rustc_allow_incoherent_impl]
|
||
#[must_use = "to lowercase the value in-place, use `make_ascii_lowercase()`"]
|
||
#[stable(feature = "ascii_methods_on_intrinsics", since = "1.23.0")]
|
||
#[inline]
|
||
pub fn to_ascii_lowercase(&self) -> String {
|
||
let mut s = self.to_owned();
|
||
s.make_ascii_lowercase();
|
||
s
|
||
}
|
||
}
|
||
|
||
/// Converts a boxed slice of bytes to a boxed string slice without checking
|
||
/// that the string contains valid UTF-8.
|
||
///
|
||
/// # Safety
|
||
///
|
||
/// * The provided bytes must contain a valid UTF-8 sequence.
|
||
///
|
||
/// # Examples
|
||
///
|
||
/// ```
|
||
/// let smile_utf8 = Box::new([226, 152, 186]);
|
||
/// let smile = unsafe { std::str::from_boxed_utf8_unchecked(smile_utf8) };
|
||
///
|
||
/// assert_eq!("☺", &*smile);
|
||
/// ```
|
||
#[stable(feature = "str_box_extras", since = "1.20.0")]
|
||
#[must_use]
|
||
#[inline]
|
||
pub unsafe fn from_boxed_utf8_unchecked(v: Box<[u8]>) -> Box<str> {
|
||
unsafe { Box::from_raw(Box::into_raw(v) as *mut str) }
|
||
}
|
||
|
||
/// Converts leading ascii bytes in `s` by calling the `convert` function.
|
||
///
|
||
/// For better average performance, this happens in chunks of `2*size_of::<usize>()`.
|
||
///
|
||
/// Returns a tuple of the converted prefix and the remainder starting from
|
||
/// the first non-ascii character.
|
||
///
|
||
/// This function is only public so that it can be verified in a codegen test,
|
||
/// see `issue-123712-str-to-lower-autovectorization.rs`.
|
||
#[unstable(feature = "str_internals", issue = "none")]
|
||
#[doc(hidden)]
|
||
#[inline]
|
||
#[cfg(not(no_global_oom_handling))]
|
||
pub fn convert_while_ascii(s: &str, convert: fn(&u8) -> u8) -> (String, &str) {
|
||
// Process the input in chunks of 16 bytes to enable auto-vectorization.
|
||
// Previously the chunk size depended on the size of `usize`,
|
||
// but on 32-bit platforms with sse or neon is also the better choice.
|
||
// The only downside on other platforms would be a bit more loop-unrolling.
|
||
const N: usize = 16;
|
||
|
||
let mut slice = s.as_bytes();
|
||
let mut out = Vec::with_capacity(slice.len());
|
||
let mut out_slice = out.spare_capacity_mut();
|
||
|
||
let mut ascii_prefix_len = 0_usize;
|
||
let mut is_ascii = [false; N];
|
||
|
||
while slice.len() >= N {
|
||
// SAFETY: checked in loop condition
|
||
let chunk = unsafe { slice.get_unchecked(..N) };
|
||
// SAFETY: out_slice has at least same length as input slice and gets sliced with the same offsets
|
||
let out_chunk = unsafe { out_slice.get_unchecked_mut(..N) };
|
||
|
||
for j in 0..N {
|
||
is_ascii[j] = chunk[j] <= 127;
|
||
}
|
||
|
||
// Auto-vectorization for this check is a bit fragile, sum and comparing against the chunk
|
||
// size gives the best result, specifically a pmovmsk instruction on x86.
|
||
// See https://github.com/llvm/llvm-project/issues/96395 for why llvm currently does not
|
||
// currently recognize other similar idioms.
|
||
if is_ascii.iter().map(|x| *x as u8).sum::<u8>() as usize != N {
|
||
break;
|
||
}
|
||
|
||
for j in 0..N {
|
||
out_chunk[j] = MaybeUninit::new(convert(&chunk[j]));
|
||
}
|
||
|
||
ascii_prefix_len += N;
|
||
slice = unsafe { slice.get_unchecked(N..) };
|
||
out_slice = unsafe { out_slice.get_unchecked_mut(N..) };
|
||
}
|
||
|
||
// handle the remainder as individual bytes
|
||
while slice.len() > 0 {
|
||
let byte = slice[0];
|
||
if byte > 127 {
|
||
break;
|
||
}
|
||
// SAFETY: out_slice has at least same length as input slice
|
||
unsafe {
|
||
*out_slice.get_unchecked_mut(0) = MaybeUninit::new(convert(&byte));
|
||
}
|
||
ascii_prefix_len += 1;
|
||
slice = unsafe { slice.get_unchecked(1..) };
|
||
out_slice = unsafe { out_slice.get_unchecked_mut(1..) };
|
||
}
|
||
|
||
unsafe {
|
||
// SAFETY: ascii_prefix_len bytes have been initialized above
|
||
out.set_len(ascii_prefix_len);
|
||
|
||
// SAFETY: We have written only valid ascii to the output vec
|
||
let ascii_string = String::from_utf8_unchecked(out);
|
||
|
||
// SAFETY: we know this is a valid char boundary
|
||
// since we only skipped over leading ascii bytes
|
||
let rest = core::str::from_utf8_unchecked(slice);
|
||
|
||
(ascii_string, rest)
|
||
}
|
||
}
|
||
#[inline]
|
||
#[cfg(not(no_global_oom_handling))]
|
||
#[allow(dead_code)]
|
||
/// Faster implementation of string replacement for ASCII to ASCII cases.
|
||
/// Should produce fast vectorized code.
|
||
unsafe fn replace_ascii(utf8_bytes: &[u8], from: u8, to: u8) -> String {
|
||
let result: Vec<u8> = utf8_bytes.iter().map(|b| if *b == from { to } else { *b }).collect();
|
||
// SAFETY: We replaced ascii with ascii on valid utf8 strings.
|
||
unsafe { String::from_utf8_unchecked(result) }
|
||
}
|