src/liballoc/str.rs

   1 // Copyright 2012-2017 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 //! Unicode string slices.
  12 //!
  13 //! The `&str` type is one of the two main string types, the other being `String`.
  14 //! Unlike its `String` counterpart, its contents are borrowed.
  15 //!
  16 //! # Basic Usage
  17 //!
  18 //! A basic string declaration of `&str` type:
  19 //!
  20 //! ```
  21 //! let hello_world = "Hello, World!";
  22 //! ```
  23 //!
  24 //! Here we have declared a string literal, also known as a string slice.
  25 //! String literals have a static lifetime, which means the string `hello_world`
  26 //! is guaranteed to be valid for the duration of the entire program.
  27 //! We can explicitly specify `hello_world`'s lifetime as well:
  28 //!
  29 //! ```
  30 //! let hello_world: &'static str = "Hello, world!";
  31 //! ```
  32 //!
  33 //! *[See also the `str` primitive type](../../std/primitive.str.html).*
  34
  35 #![stable(feature = "rust1", since = "1.0.0")]
  36
  37 // Many of the usings in this module are only used in the test configuration.
  38 // It's cleaner to just turn off the unused_imports warning than to fix them.
  39 #![allow(unused_imports)]
  40
  41 use core::fmt;
  42 use core::str as core_str;
  43 use core::str::pattern::Pattern;
  44 use core::str::pattern::{Searcher, ReverseSearcher, DoubleEndedSearcher};
  45 use core::mem;
  46 use core::iter::FusedIterator;
  47 use std_unicode::str::{UnicodeStr, Utf16Encoder};
  48
  49 use vec_deque::VecDeque;
  50 use borrow::{Borrow, ToOwned};
  51 use string::String;
  52 use std_unicode;
  53 use vec::Vec;
  54 use slice::{SliceConcatExt, SliceIndex};
  55 use boxed::Box;
  56
  57 #[stable(feature = "rust1", since = "1.0.0")]
  58 pub use core::str::{FromStr, Utf8Error};
  59 #[allow(deprecated)]
  60 #[stable(feature = "rust1", since = "1.0.0")]
  61 pub use core::str::{Lines, LinesAny};
  62 #[stable(feature = "rust1", since = "1.0.0")]
  63 pub use core::str::{Split, RSplit};
  64 #[stable(feature = "rust1", since = "1.0.0")]
  65 pub use core::str::{SplitN, RSplitN};
  66 #[stable(feature = "rust1", since = "1.0.0")]
  67 pub use core::str::{SplitTerminator, RSplitTerminator};
  68 #[stable(feature = "rust1", since = "1.0.0")]
  69 pub use core::str::{Matches, RMatches};
  70 #[stable(feature = "rust1", since = "1.0.0")]
  71 pub use core::str::{MatchIndices, RMatchIndices};
  72 #[stable(feature = "rust1", since = "1.0.0")]
  73 pub use core::str::{from_utf8, from_utf8_mut, Chars, CharIndices, Bytes};
  74 #[stable(feature = "rust1", since = "1.0.0")]
  75 pub use core::str::{from_utf8_unchecked, from_utf8_unchecked_mut, ParseBoolError};
  76 #[stable(feature = "rust1", since = "1.0.0")]
  77 pub use std_unicode::str::SplitWhitespace;
  78 #[stable(feature = "rust1", since = "1.0.0")]
  79 pub use core::str::pattern;
  80
  81
  82 #[unstable(feature = "slice_concat_ext",
  83            reason = "trait should not have to exist",
  84            issue = "27747")]
  85 impl<S: Borrow<str>> SliceConcatExt<str> for [S] {
  86     type Output = String;
  87
  88     fn concat(&self) -> String {
  89         if self.is_empty() {
  90             return String::new();
  91         }
  92
  93         // `len` calculation may overflow but push_str will check boundaries
  94         let len = self.iter().map(|s| s.borrow().len()).sum();
  95         let mut result = String::with_capacity(len);
  96
  97         for s in self {
  98             result.push_str(s.borrow())
  99         }
 100
 101         result
 102     }
 103
 104     fn join(&self, sep: &str) -> String {
 105         if self.is_empty() {
 106             return String::new();
 107         }
 108
 109         // concat is faster
 110         if sep.is_empty() {
 111             return self.concat();
 112         }
 113
 114         // this is wrong without the guarantee that `self` is non-empty
 115         // `len` calculation may overflow but push_str but will check boundaries
 116         let len = sep.len() * (self.len() - 1) +
 117                   self.iter().map(|s| s.borrow().len()).sum::<usize>();
 118         let mut result = String::with_capacity(len);
 119         let mut first = true;
 120
 121         for s in self {
 122             if first {
 123                 first = false;
 124             } else {
 125                 result.push_str(sep);
 126             }
 127             result.push_str(s.borrow());
 128         }
 129         result
 130     }
 131
 132     fn connect(&self, sep: &str) -> String {
 133         self.join(sep)
 134     }
 135 }
 136
 137 /// An iterator of [`u16`] over the string encoded as UTF-16.
 138 ///
 139 /// [`u16`]: ../../std/primitive.u16.html
 140 ///
 141 /// This struct is created by the [`encode_utf16`] method on [`str`].
 142 /// See its documentation for more.
 143 ///
 144 /// [`encode_utf16`]: ../../std/primitive.str.html#method.encode_utf16
 145 /// [`str`]: ../../std/primitive.str.html
 146 #[derive(Clone)]
 147 #[stable(feature = "encode_utf16", since = "1.8.0")]
 148 pub struct EncodeUtf16<'a> {
 149     encoder: Utf16Encoder<Chars<'a>>,
 150 }
 151
 152 #[stable(feature = "collection_debug", since = "1.17.0")]
 153 impl<'a> fmt::Debug for EncodeUtf16<'a> {
 154     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
 155         f.pad("EncodeUtf16 { .. }")
 156     }
 157 }
 158
 159 #[stable(feature = "encode_utf16", since = "1.8.0")]
 160 impl<'a> Iterator for EncodeUtf16<'a> {
 161     type Item = u16;
 162
 163     #[inline]
 164     fn next(&mut self) -> Option<u16> {
 165         self.encoder.next()
 166     }
 167
 168     #[inline]
 169     fn size_hint(&self) -> (usize, Option<usize>) {
 170         self.encoder.size_hint()
 171     }
 172 }
 173
 174 #[unstable(feature = "fused", issue = "35602")]
 175 impl<'a> FusedIterator for EncodeUtf16<'a> {}
 176
 177 #[stable(feature = "rust1", since = "1.0.0")]
 178 impl Borrow<str> for String {
 179     #[inline]
 180     fn borrow(&self) -> &str {
 181         &self[..]
 182     }
 183 }
 184
 185 #[stable(feature = "rust1", since = "1.0.0")]
 186 impl ToOwned for str {
 187     type Owned = String;
 188     fn to_owned(&self) -> String {
 189         unsafe { String::from_utf8_unchecked(self.as_bytes().to_owned()) }
 190     }
 191
 192     fn clone_into(&self, target: &mut String) {
 193         let mut b = mem::replace(target, String::new()).into_bytes();
 194         self.as_bytes().clone_into(&mut b);
 195         *target = unsafe { String::from_utf8_unchecked(b) }
 196     }
 197 }
 198
 199 /// Methods for string slices.
 200 #[lang = "str"]
 201 #[cfg(not(test))]
 202 impl str {
 203     /// Returns the length of `self`.
 204     ///
 205     /// This length is in bytes, not [`char`]s or graphemes. In other words,
 206     /// it may not be what a human considers the length of the string.
 207     ///
 208     /// [`char`]: primitive.char.html
 209     ///
 210     /// # Examples
 211     ///
 212     /// Basic usage:
 213     ///
 214     /// ```
 215     /// let len = "foo".len();
 216     /// assert_eq!(3, len);
 217     ///
 218     /// let len = "ƒoo".len(); // fancy f!
 219     /// assert_eq!(4, len);
 220     /// ```
 221     #[stable(feature = "rust1", since = "1.0.0")]
 222     #[inline]
 223     pub fn len(&self) -> usize {
 224         core_str::StrExt::len(self)
 225     }
 226
 227     /// Returns `true` if `self` has a length of zero bytes.
 228     ///
 229     /// # Examples
 230     ///
 231     /// Basic usage:
 232     ///
 233     /// ```
 234     /// let s = "";
 235     /// assert!(s.is_empty());
 236     ///
 237     /// let s = "not empty";
 238     /// assert!(!s.is_empty());
 239     /// ```
 240     #[inline]
 241     #[stable(feature = "rust1", since = "1.0.0")]
 242     pub fn is_empty(&self) -> bool {
 243         core_str::StrExt::is_empty(self)
 244     }
 245
 246     /// Checks that `index`-th byte lies at the start and/or end of a
 247     /// UTF-8 code point sequence.
 248     ///
 249     /// The start and end of the string (when `index == self.len()`) are
 250     /// considered to be
 251     /// boundaries.
 252     ///
 253     /// Returns `false` if `index` is greater than `self.len()`.
 254     ///
 255     /// # Examples
 256     ///
 257     /// ```
 258     /// let s = "Löwe 老虎 Léopard";
 259     /// assert!(s.is_char_boundary(0));
 260     /// // start of `老`
 261     /// assert!(s.is_char_boundary(6));
 262     /// assert!(s.is_char_boundary(s.len()));
 263     ///
 264     /// // second byte of `ö`
 265     /// assert!(!s.is_char_boundary(2));
 266     ///
 267     /// // third byte of `老`
 268     /// assert!(!s.is_char_boundary(8));
 269     /// ```
 270     #[stable(feature = "is_char_boundary", since = "1.9.0")]
 271     #[inline]
 272     pub fn is_char_boundary(&self, index: usize) -> bool {
 273         core_str::StrExt::is_char_boundary(self, index)
 274     }
 275
 276     /// Converts a string slice to a byte slice. To convert the byte slice back
 277     /// into a string slice, use the [`str::from_utf8`] function.
 278     ///
 279     /// [`str::from_utf8`]: ./str/fn.from_utf8.html
 280     ///
 281     /// # Examples
 282     ///
 283     /// Basic usage:
 284     ///
 285     /// ```
 286     /// let bytes = "bors".as_bytes();
 287     /// assert_eq!(b"bors", bytes);
 288     /// ```
 289     #[stable(feature = "rust1", since = "1.0.0")]
 290     #[inline(always)]
 291     pub fn as_bytes(&self) -> &[u8] {
 292         core_str::StrExt::as_bytes(self)
 293     }
 294
 295     /// Converts a mutable string slice to a mutable byte slice. To convert the
 296     /// mutable byte slice back into a mutable string slice, use the
 297     /// [`str::from_utf8_mut`] function.
 298     ///
 299     /// [`str::from_utf8_mut`]: ./str/fn.from_utf8_mut.html
 300     #[stable(feature = "str_mut_extras", since = "1.20.0")]
 301     #[inline(always)]
 302     pub unsafe fn as_bytes_mut(&mut self) -> &mut [u8] {
 303         core_str::StrExt::as_bytes_mut(self)
 304     }
 305
 306     /// Converts a string slice to a raw pointer.
 307     ///
 308     /// As string slices are a slice of bytes, the raw pointer points to a
 309     /// [`u8`]. This pointer will be pointing to the first byte of the string
 310     /// slice.
 311     ///
 312     /// [`u8`]: primitive.u8.html
 313     ///
 314     /// # Examples
 315     ///
 316     /// Basic usage:
 317     ///
 318     /// ```
 319     /// let s = "Hello";
 320     /// let ptr = s.as_ptr();
 321     /// ```
 322     #[stable(feature = "rust1", since = "1.0.0")]
 323     #[inline]
 324     pub fn as_ptr(&self) -> *const u8 {
 325         core_str::StrExt::as_ptr(self)
 326     }
 327
 328     /// Returns a subslice of `str`.
 329     ///
 330     /// This is the non-panicking alternative to indexing the `str`. Returns
 331     /// [`None`] whenever equivalent indexing operation would panic.
 332     ///
 333     /// [`None`]: option/enum.Option.html#variant.None
 334     ///
 335     /// # Examples
 336     ///
 337     /// ```
 338     /// let mut v = String::from("🗻∈🌏");
 339     ///
 340     /// assert_eq!(Some("🗻"), v.get(0..4));
 341     ///
 342     /// // indices not on UTF-8 sequence boundaries
 343     /// assert!(v.get_mut(1..).is_none());
 344     /// assert!(v.get_mut(..8).is_none());
 345     ///
 346     /// // out of bounds
 347     /// assert!(v.get_mut(..42).is_none());
 348     /// ```
 349     #[stable(feature = "str_checked_slicing", since = "1.20.0")]
 350     #[inline]
 351     pub fn get<I: SliceIndex<str>>(&self, i: I) -> Option<&I::Output> {
 352         core_str::StrExt::get(self, i)
 353     }
 354
 355     /// Returns a mutable subslice of `str`.
 356     ///
 357     /// This is the non-panicking alternative to indexing the `str`. Returns
 358     /// [`None`] whenever equivalent indexing operation would panic.
 359     ///
 360     /// [`None`]: option/enum.Option.html#variant.None
 361     ///
 362     /// # Examples
 363     ///
 364     /// ```
 365     /// let mut v = String::from("🗻∈🌏");
 366     ///
 367     /// assert_eq!(Some("🗻"), v.get_mut(0..4).map(|v| &*v));
 368     ///
 369     /// // indices not on UTF-8 sequence boundaries
 370     /// assert!(v.get_mut(1..).is_none());
 371     /// assert!(v.get_mut(..8).is_none());
 372     ///
 373     /// // out of bounds
 374     /// assert!(v.get_mut(..42).is_none());
 375     /// ```
 376     #[stable(feature = "str_checked_slicing", since = "1.20.0")]
 377     #[inline]
 378     pub fn get_mut<I: SliceIndex<str>>(&mut self, i: I) -> Option<&mut I::Output> {
 379         core_str::StrExt::get_mut(self, i)
 380     }
 381
 382     /// Returns a unchecked subslice of `str`.
 383     ///
 384     /// This is the unchecked alternative to indexing the `str`.
 385     ///
 386     /// # Safety
 387     ///
 388     /// Callers of this function are responsible that these preconditions are
 389     /// satisfied:
 390     ///
 391     /// * The starting index must come before the ending index;
 392     /// * Indexes must be within bounds of the original slice;
 393     /// * Indexes must lie on UTF-8 sequence boundaries.
 394     ///
 395     /// Failing that, the returned string slice may reference invalid memory or
 396     /// violate the invariants communicated by the `str` type.
 397     ///
 398     /// # Examples
 399     ///
 400     /// ```
 401     /// let v = "🗻∈🌏";
 402     /// unsafe {
 403     ///     assert_eq!("🗻", v.get_unchecked(0..4));
 404     ///     assert_eq!("∈", v.get_unchecked(4..7));
 405     ///     assert_eq!("🌏", v.get_unchecked(7..11));
 406     /// }
 407     /// ```
 408     #[stable(feature = "str_checked_slicing", since = "1.20.0")]
 409     #[inline]
 410     pub unsafe fn get_unchecked<I: SliceIndex<str>>(&self, i: I) -> &I::Output {
 411         core_str::StrExt::get_unchecked(self, i)
 412     }
 413
 414     /// Returns a mutable, unchecked subslice of `str`.
 415     ///
 416     /// This is the unchecked alternative to indexing the `str`.
 417     ///
 418     /// # Safety
 419     ///
 420     /// Callers of this function are responsible that these preconditions are
 421     /// satisfied:
 422     ///
 423     /// * The starting index must come before the ending index;
 424     /// * Indexes must be within bounds of the original slice;
 425     /// * Indexes must lie on UTF-8 sequence boundaries.
 426     ///
 427     /// Failing that, the returned string slice may reference invalid memory or
 428     /// violate the invariants communicated by the `str` type.
 429     ///
 430     /// # Examples
 431     ///
 432     /// ```
 433     /// let mut v = String::from("🗻∈🌏");
 434     /// unsafe {
 435     ///     assert_eq!("🗻", v.get_unchecked_mut(0..4));
 436     ///     assert_eq!("∈", v.get_unchecked_mut(4..7));
 437     ///     assert_eq!("🌏", v.get_unchecked_mut(7..11));
 438     /// }
 439     /// ```
 440     #[stable(feature = "str_checked_slicing", since = "1.20.0")]
 441     #[inline]
 442     pub unsafe fn get_unchecked_mut<I: SliceIndex<str>>(&mut self, i: I) -> &mut I::Output {
 443         core_str::StrExt::get_unchecked_mut(self, i)
 444     }
 445
 446     /// Creates a string slice from another string slice, bypassing safety
 447     /// checks.
 448     ///
 449     /// This is generally not recommended, use with caution! For a safe
 450     /// alternative see [`str`] and [`Index`].
 451     ///
 452     /// [`str`]: primitive.str.html
 453     /// [`Index`]: ops/trait.Index.html
 454     ///
 455     /// This new slice goes from `begin` to `end`, including `begin` but
 456     /// excluding `end`.
 457     ///
 458     /// To get a mutable string slice instead, see the
 459     /// [`slice_mut_unchecked`] method.
 460     ///
 461     /// [`slice_mut_unchecked`]: #method.slice_mut_unchecked
 462     ///
 463     /// # Safety
 464     ///
 465     /// Callers of this function are responsible that three preconditions are
 466     /// satisfied:
 467     ///
 468     /// * `begin` must come before `end`.
 469     /// * `begin` and `end` must be byte positions within the string slice.
 470     /// * `begin` and `end` must lie on UTF-8 sequence boundaries.
 471     ///
 472     /// # Examples
 473     ///
 474     /// Basic usage:
 475     ///
 476     /// ```
 477     /// let s = "Löwe 老虎 Léopard";
 478     ///
 479     /// unsafe {
 480     ///     assert_eq!("Löwe 老虎 Léopard", s.slice_unchecked(0, 21));
 481     /// }
 482     ///
 483     /// let s = "Hello, world!";
 484     ///
 485     /// unsafe {
 486     ///     assert_eq!("world", s.slice_unchecked(7, 12));
 487     /// }
 488     /// ```
 489     #[stable(feature = "rust1", since = "1.0.0")]
 490     #[inline]
 491     pub unsafe fn slice_unchecked(&self, begin: usize, end: usize) -> &str {
 492         core_str::StrExt::slice_unchecked(self, begin, end)
 493     }
 494
 495     /// Creates a string slice from another string slice, bypassing safety
 496     /// checks.
 497     /// This is generally not recommended, use with caution! For a safe
 498     /// alternative see [`str`] and [`IndexMut`].
 499     ///
 500     /// [`str`]: primitive.str.html
 501     /// [`IndexMut`]: ops/trait.IndexMut.html
 502     ///
 503     /// This new slice goes from `begin` to `end`, including `begin` but
 504     /// excluding `end`.
 505     ///
 506     /// To get an immutable string slice instead, see the
 507     /// [`slice_unchecked`] method.
 508     ///
 509     /// [`slice_unchecked`]: #method.slice_unchecked
 510     ///
 511     /// # Safety
 512     ///
 513     /// Callers of this function are responsible that three preconditions are
 514     /// satisfied:
 515     ///
 516     /// * `begin` must come before `end`.
 517     /// * `begin` and `end` must be byte positions within the string slice.
 518     /// * `begin` and `end` must lie on UTF-8 sequence boundaries.
 519     #[stable(feature = "str_slice_mut", since = "1.5.0")]
 520     #[inline]
 521     pub unsafe fn slice_mut_unchecked(&mut self, begin: usize, end: usize) -> &mut str {
 522         core_str::StrExt::slice_mut_unchecked(self, begin, end)
 523     }
 524
 525     /// Divide one string slice into two at an index.
 526     ///
 527     /// The argument, `mid`, should be a byte offset from the start of the
 528     /// string. It must also be on the boundary of a UTF-8 code point.
 529     ///
 530     /// The two slices returned go from the start of the string slice to `mid`,
 531     /// and from `mid` to the end of the string slice.
 532     ///
 533     /// To get mutable string slices instead, see the [`split_at_mut`]
 534     /// method.
 535     ///
 536     /// [`split_at_mut`]: #method.split_at_mut
 537     ///
 538     /// # Panics
 539     ///
 540     /// Panics if `mid` is not on a UTF-8 code point boundary, or if it is
 541     /// beyond the last code point of the string slice.
 542     ///
 543     /// # Examples
 544     ///
 545     /// Basic usage:
 546     ///
 547     /// ```
 548     /// let s = "Per Martin-Löf";
 549     ///
 550     /// let (first, last) = s.split_at(3);
 551     ///
 552     /// assert_eq!("Per", first);
 553     /// assert_eq!(" Martin-Löf", last);
 554     /// ```
 555     #[inline]
 556     #[stable(feature = "str_split_at", since = "1.4.0")]
 557     pub fn split_at(&self, mid: usize) -> (&str, &str) {
 558         core_str::StrExt::split_at(self, mid)
 559     }
 560
 561     /// Divide one mutable string slice into two at an index.
 562     ///
 563     /// The argument, `mid`, should be a byte offset from the start of the
 564     /// string. It must also be on the boundary of a UTF-8 code point.
 565     ///
 566     /// The two slices returned go from the start of the string slice to `mid`,
 567     /// and from `mid` to the end of the string slice.
 568     ///
 569     /// To get immutable string slices instead, see the [`split_at`] method.
 570     ///
 571     /// [`split_at`]: #method.split_at
 572     ///
 573     /// # Panics
 574     ///
 575     /// Panics if `mid` is not on a UTF-8 code point boundary, or if it is
 576     /// beyond the last code point of the string slice.
 577     ///
 578     /// # Examples
 579     ///
 580     /// Basic usage:
 581     ///
 582     /// ```
 583     /// use std::ascii::AsciiExt;
 584     ///
 585     /// let mut s = "Per Martin-Löf".to_string();
 586     /// {
 587     ///     let (first, last) = s.split_at_mut(3);
 588     ///     first.make_ascii_uppercase();
 589     ///     assert_eq!("PER", first);
 590     ///     assert_eq!(" Martin-Löf", last);
 591     /// }
 592     /// assert_eq!("PER Martin-Löf", s);
 593     /// ```
 594     #[inline]
 595     #[stable(feature = "str_split_at", since = "1.4.0")]
 596     pub fn split_at_mut(&mut self, mid: usize) -> (&mut str, &mut str) {
 597         core_str::StrExt::split_at_mut(self, mid)
 598     }
 599
 600     /// Returns an iterator over the [`char`]s of a string slice.
 601     ///
 602     /// As a string slice consists of valid UTF-8, we can iterate through a
 603     /// string slice by [`char`]. This method returns such an iterator.
 604     ///
 605     /// It's important to remember that [`char`] represents a Unicode Scalar
 606     /// Value, and may not match your idea of what a 'character' is. Iteration
 607     /// over grapheme clusters may be what you actually want.
 608     ///
 609     /// [`char`]: primitive.char.html
 610     ///
 611     /// # Examples
 612     ///
 613     /// Basic usage:
 614     ///
 615     /// ```
 616     /// let word = "goodbye";
 617     ///
 618     /// let count = word.chars().count();
 619     /// assert_eq!(7, count);
 620     ///
 621     /// let mut chars = word.chars();
 622     ///
 623     /// assert_eq!(Some('g'), chars.next());
 624     /// assert_eq!(Some('o'), chars.next());
 625     /// assert_eq!(Some('o'), chars.next());
 626     /// assert_eq!(Some('d'), chars.next());
 627     /// assert_eq!(Some('b'), chars.next());
 628     /// assert_eq!(Some('y'), chars.next());
 629     /// assert_eq!(Some('e'), chars.next());
 630     ///
 631     /// assert_eq!(None, chars.next());
 632     /// ```
 633     ///
 634     /// Remember, [`char`]s may not match your human intuition about characters:
 635     ///
 636     /// ```
 637     /// let y = "y̆";
 638     ///
 639     /// let mut chars = y.chars();
 640     ///
 641     /// assert_eq!(Some('y'), chars.next()); // not 'y̆'
 642     /// assert_eq!(Some('\u{0306}'), chars.next());
 643     ///
 644     /// assert_eq!(None, chars.next());
 645     /// ```
 646     #[stable(feature = "rust1", since = "1.0.0")]
 647     #[inline]
 648     pub fn chars(&self) -> Chars {
 649         core_str::StrExt::chars(self)
 650     }
 651     /// Returns an iterator over the [`char`]s of a string slice, and their
 652     /// positions.
 653     ///
 654     /// As a string slice consists of valid UTF-8, we can iterate through a
 655     /// string slice by [`char`]. This method returns an iterator of both
 656     /// these [`char`]s, as well as their byte positions.
 657     ///
 658     /// The iterator yields tuples. The position is first, the [`char`] is
 659     /// second.
 660     ///
 661     /// [`char`]: primitive.char.html
 662     ///
 663     /// # Examples
 664     ///
 665     /// Basic usage:
 666     ///
 667     /// ```
 668     /// let word = "goodbye";
 669     ///
 670     /// let count = word.char_indices().count();
 671     /// assert_eq!(7, count);
 672     ///
 673     /// let mut char_indices = word.char_indices();
 674     ///
 675     /// assert_eq!(Some((0, 'g')), char_indices.next());
 676     /// assert_eq!(Some((1, 'o')), char_indices.next());
 677     /// assert_eq!(Some((2, 'o')), char_indices.next());
 678     /// assert_eq!(Some((3, 'd')), char_indices.next());
 679     /// assert_eq!(Some((4, 'b')), char_indices.next());
 680     /// assert_eq!(Some((5, 'y')), char_indices.next());
 681     /// assert_eq!(Some((6, 'e')), char_indices.next());
 682     ///
 683     /// assert_eq!(None, char_indices.next());
 684     /// ```
 685     ///
 686     /// Remember, [`char`]s may not match your human intuition about characters:
 687     ///
 688     /// ```
 689     /// let y = "y̆";
 690     ///
 691     /// let mut char_indices = y.char_indices();
 692     ///
 693     /// assert_eq!(Some((0, 'y')), char_indices.next()); // not (0, 'y̆')
 694     /// assert_eq!(Some((1, '\u{0306}')), char_indices.next());
 695     ///
 696     /// assert_eq!(None, char_indices.next());
 697     /// ```
 698     #[stable(feature = "rust1", since = "1.0.0")]
 699     #[inline]
 700     pub fn char_indices(&self) -> CharIndices {
 701         core_str::StrExt::char_indices(self)
 702     }
 703
 704     /// An iterator over the bytes of a string slice.
 705     ///
 706     /// As a string slice consists of a sequence of bytes, we can iterate
 707     /// through a string slice by byte. This method returns such an iterator.
 708     ///
 709     /// # Examples
 710     ///
 711     /// Basic usage:
 712     ///
 713     /// ```
 714     /// let mut bytes = "bors".bytes();
 715     ///
 716     /// assert_eq!(Some(b'b'), bytes.next());
 717     /// assert_eq!(Some(b'o'), bytes.next());
 718     /// assert_eq!(Some(b'r'), bytes.next());
 719     /// assert_eq!(Some(b's'), bytes.next());
 720     ///
 721     /// assert_eq!(None, bytes.next());
 722     /// ```
 723     #[stable(feature = "rust1", since = "1.0.0")]
 724     #[inline]
 725     pub fn bytes(&self) -> Bytes {
 726         core_str::StrExt::bytes(self)
 727     }
 728
 729     /// Split a string slice by whitespace.
 730     ///
 731     /// The iterator returned will return string slices that are sub-slices of
 732     /// the original string slice, separated by any amount of whitespace.
 733     ///
 734     /// 'Whitespace' is defined according to the terms of the Unicode Derived
 735     /// Core Property `White_Space`.
 736     ///
 737     /// # Examples
 738     ///
 739     /// Basic usage:
 740     ///
 741     /// ```
 742     /// let mut iter = "A few words".split_whitespace();
 743     ///
 744     /// assert_eq!(Some("A"), iter.next());
 745     /// assert_eq!(Some("few"), iter.next());
 746     /// assert_eq!(Some("words"), iter.next());
 747     ///
 748     /// assert_eq!(None, iter.next());
 749     /// ```
 750     ///
 751     /// All kinds of whitespace are considered:
 752     ///
 753     /// ```
 754     /// let mut iter = " Mary   had\ta\u{2009}little  \n\t lamb".split_whitespace();
 755     /// assert_eq!(Some("Mary"), iter.next());
 756     /// assert_eq!(Some("had"), iter.next());
 757     /// assert_eq!(Some("a"), iter.next());
 758     /// assert_eq!(Some("little"), iter.next());
 759     /// assert_eq!(Some("lamb"), iter.next());
 760     ///
 761     /// assert_eq!(None, iter.next());
 762     /// ```
 763     #[stable(feature = "split_whitespace", since = "1.1.0")]
 764     #[inline]
 765     pub fn split_whitespace(&self) -> SplitWhitespace {
 766         UnicodeStr::split_whitespace(self)
 767     }
 768
 769     /// An iterator over the lines of a string, as string slices.
 770     ///
 771     /// Lines are ended with either a newline (`\n`) or a carriage return with
 772     /// a line feed (`\r\n`).
 773     ///
 774     /// The final line ending is optional.
 775     ///
 776     /// # Examples
 777     ///
 778     /// Basic usage:
 779     ///
 780     /// ```
 781     /// let text = "foo\r\nbar\n\nbaz\n";
 782     /// let mut lines = text.lines();
 783     ///
 784     /// assert_eq!(Some("foo"), lines.next());
 785     /// assert_eq!(Some("bar"), lines.next());
 786     /// assert_eq!(Some(""), lines.next());
 787     /// assert_eq!(Some("baz"), lines.next());
 788     ///
 789     /// assert_eq!(None, lines.next());
 790     /// ```
 791     ///
 792     /// The final line ending isn't required:
 793     ///
 794     /// ```
 795     /// let text = "foo\nbar\n\r\nbaz";
 796     /// let mut lines = text.lines();
 797     ///
 798     /// assert_eq!(Some("foo"), lines.next());
 799     /// assert_eq!(Some("bar"), lines.next());
 800     /// assert_eq!(Some(""), lines.next());
 801     /// assert_eq!(Some("baz"), lines.next());
 802     ///
 803     /// assert_eq!(None, lines.next());
 804     /// ```
 805     #[stable(feature = "rust1", since = "1.0.0")]
 806     #[inline]
 807     pub fn lines(&self) -> Lines {
 808         core_str::StrExt::lines(self)
 809     }
 810
 811     /// An iterator over the lines of a string.
 812     #[stable(feature = "rust1", since = "1.0.0")]
 813     #[rustc_deprecated(since = "1.4.0", reason = "use lines() instead now")]
 814     #[inline]
 815     #[allow(deprecated)]
 816     pub fn lines_any(&self) -> LinesAny {
 817         core_str::StrExt::lines_any(self)
 818     }
 819
 820     /// Returns an iterator of `u16` over the string encoded as UTF-16.
 821     #[stable(feature = "encode_utf16", since = "1.8.0")]
 822     pub fn encode_utf16(&self) -> EncodeUtf16 {
 823         EncodeUtf16 { encoder: Utf16Encoder::new(self[..].chars()) }
 824     }
 825
 826     /// Returns `true` if the given pattern matches a sub-slice of
 827     /// this string slice.
 828     ///
 829     /// Returns `false` if it does not.
 830     ///
 831     /// # Examples
 832     ///
 833     /// Basic usage:
 834     ///
 835     /// ```
 836     /// let bananas = "bananas";
 837     ///
 838     /// assert!(bananas.contains("nana"));
 839     /// assert!(!bananas.contains("apples"));
 840     /// ```
 841     #[stable(feature = "rust1", since = "1.0.0")]
 842     #[inline]
 843     pub fn contains<'a, P: Pattern<'a>>(&'a self, pat: P) -> bool {
 844         core_str::StrExt::contains(self, pat)
 845     }
 846
 847     /// Returns `true` if the given pattern matches a prefix of this
 848     /// string slice.
 849     ///
 850     /// Returns `false` if it does not.
 851     ///
 852     /// # Examples
 853     ///
 854     /// Basic usage:
 855     ///
 856     /// ```
 857     /// let bananas = "bananas";
 858     ///
 859     /// assert!(bananas.starts_with("bana"));
 860     /// assert!(!bananas.starts_with("nana"));
 861     /// ```
 862     #[stable(feature = "rust1", since = "1.0.0")]
 863     pub fn starts_with<'a, P: Pattern<'a>>(&'a self, pat: P) -> bool {
 864         core_str::StrExt::starts_with(self, pat)
 865     }
 866
 867     /// Returns `true` if the given pattern matches a suffix of this
 868     /// string slice.
 869     ///
 870     /// Returns `false` if it does not.
 871     ///
 872     /// # Examples
 873     ///
 874     /// Basic usage:
 875     ///
 876     /// ```
 877     /// let bananas = "bananas";
 878     ///
 879     /// assert!(bananas.ends_with("anas"));
 880     /// assert!(!bananas.ends_with("nana"));
 881     /// ```
 882     #[stable(feature = "rust1", since = "1.0.0")]
 883     pub fn ends_with<'a, P: Pattern<'a>>(&'a self, pat: P) -> bool
 884         where P::Searcher: ReverseSearcher<'a>
 885     {
 886         core_str::StrExt::ends_with(self, pat)
 887     }
 888
 889     /// Returns the byte index of the first character of this string slice that
 890     /// matches the pattern.
 891     ///
 892     /// Returns [`None`] if the pattern doesn't match.
 893     ///
 894     /// The pattern can be a `&str`, [`char`], or a closure that determines if
 895     /// a character matches.
 896     ///
 897     /// [`char`]: primitive.char.html
 898     /// [`None`]: option/enum.Option.html#variant.None
 899     ///
 900     /// # Examples
 901     ///
 902     /// Simple patterns:
 903     ///
 904     /// ```
 905     /// let s = "Löwe 老虎 Léopard";
 906     ///
 907     /// assert_eq!(s.find('L'), Some(0));
 908     /// assert_eq!(s.find('é'), Some(14));
 909     /// assert_eq!(s.find("Léopard"), Some(13));
 910     /// ```
 911     ///
 912     /// More complex patterns with closures:
 913     ///
 914     /// ```
 915     /// let s = "Löwe 老虎 Léopard";
 916     ///
 917     /// assert_eq!(s.find(char::is_whitespace), Some(5));
 918     /// assert_eq!(s.find(char::is_lowercase), Some(1));
 919     /// ```
 920     ///
 921     /// Not finding the pattern:
 922     ///
 923     /// ```
 924     /// let s = "Löwe 老虎 Léopard";
 925     /// let x: &[_] = &['1', '2'];
 926     ///
 927     /// assert_eq!(s.find(x), None);
 928     /// ```
 929     #[stable(feature = "rust1", since = "1.0.0")]
 930     #[inline]
 931     pub fn find<'a, P: Pattern<'a>>(&'a self, pat: P) -> Option<usize> {
 932         core_str::StrExt::find(self, pat)
 933     }
 934
 935     /// Returns the byte index of the last character of this string slice that
 936     /// matches the pattern.
 937     ///
 938     /// Returns [`None`] if the pattern doesn't match.
 939     ///
 940     /// The pattern can be a `&str`, [`char`], or a closure that determines if
 941     /// a character matches.
 942     ///
 943     /// [`char`]: primitive.char.html
 944     /// [`None`]: option/enum.Option.html#variant.None
 945     ///
 946     /// # Examples
 947     ///
 948     /// Simple patterns:
 949     ///
 950     /// ```
 951     /// let s = "Löwe 老虎 Léopard";
 952     ///
 953     /// assert_eq!(s.rfind('L'), Some(13));
 954     /// assert_eq!(s.rfind('é'), Some(14));
 955     /// ```
 956     ///
 957     /// More complex patterns with closures:
 958     ///
 959     /// ```
 960     /// let s = "Löwe 老虎 Léopard";
 961     ///
 962     /// assert_eq!(s.rfind(char::is_whitespace), Some(12));
 963     /// assert_eq!(s.rfind(char::is_lowercase), Some(20));
 964     /// ```
 965     ///
 966     /// Not finding the pattern:
 967     ///
 968     /// ```
 969     /// let s = "Löwe 老虎 Léopard";
 970     /// let x: &[_] = &['1', '2'];
 971     ///
 972     /// assert_eq!(s.rfind(x), None);
 973     /// ```
 974     #[stable(feature = "rust1", since = "1.0.0")]
 975     #[inline]
 976     pub fn rfind<'a, P: Pattern<'a>>(&'a self, pat: P) -> Option<usize>
 977         where P::Searcher: ReverseSearcher<'a>
 978     {
 979         core_str::StrExt::rfind(self, pat)
 980     }
 981
 982     /// An iterator over substrings of this string slice, separated by
 983     /// characters matched by a pattern.
 984     ///
 985     /// The pattern can be a `&str`, [`char`], or a closure that determines the
 986     /// split.
 987     ///
 988     /// # Iterator behavior
 989     ///
 990     /// The returned iterator will be a [`DoubleEndedIterator`] if the pattern
 991     /// allows a reverse search and forward/reverse search yields the same
 992     /// elements. This is true for, eg, [`char`] but not for `&str`.
 993     ///
 994     /// [`DoubleEndedIterator`]: iter/trait.DoubleEndedIterator.html
 995     ///
 996     /// If the pattern allows a reverse search but its results might differ
 997     /// from a forward search, the [`rsplit`] method can be used.
 998     ///
 999     /// [`char`]: primitive.char.html
1000     /// [`rsplit`]: #method.rsplit
1001     ///
1002     /// # Examples
1003     ///
1004     /// Simple patterns:
1005     ///
1006     /// ```
1007     /// let v: Vec<&str> = "Mary had a little lamb".split(' ').collect();
1008     /// assert_eq!(v, ["Mary", "had", "a", "little", "lamb"]);
1009     ///
1010     /// let v: Vec<&str> = "".split('X').collect();
1011     /// assert_eq!(v, [""]);
1012     ///
1013     /// let v: Vec<&str> = "lionXXtigerXleopard".split('X').collect();
1014     /// assert_eq!(v, ["lion", "", "tiger", "leopard"]);
1015     ///
1016     /// let v: Vec<&str> = "lion::tiger::leopard".split("::").collect();
1017     /// assert_eq!(v, ["lion", "tiger", "leopard"]);
1018     ///
1019     /// let v: Vec<&str> = "abc1def2ghi".split(char::is_numeric).collect();
1020     /// assert_eq!(v, ["abc", "def", "ghi"]);
1021     ///
1022     /// let v: Vec<&str> = "lionXtigerXleopard".split(char::is_uppercase).collect();
1023     /// assert_eq!(v, ["lion", "tiger", "leopard"]);
1024     /// ```
1025     ///
1026     /// A more complex pattern, using a closure:
1027     ///
1028     /// ```
1029     /// let v: Vec<&str> = "abc1defXghi".split(|c| c == '1' || c == 'X').collect();
1030     /// assert_eq!(v, ["abc", "def", "ghi"]);
1031     /// ```
1032     ///
1033     /// If a string contains multiple contiguous separators, you will end up
1034     /// with empty strings in the output:
1035     ///
1036     /// ```
1037     /// let x = "||||a||b|c".to_string();
1038     /// let d: Vec<_> = x.split('|').collect();
1039     ///
1040     /// assert_eq!(d, &["", "", "", "", "a", "", "b", "c"]);
1041     /// ```
1042     ///
1043     /// Contiguous separators are separated by the empty string.
1044     ///
1045     /// ```
1046     /// let x = "(///)".to_string();
1047     /// let d: Vec<_> = x.split('/').collect();
1048     ///
1049     /// assert_eq!(d, &["(", "", "", ")"]);
1050     /// ```
1051     ///
1052     /// Separators at the start or end of a string are neighbored
1053     /// by empty strings.
1054     ///
1055     /// ```
1056     /// let d: Vec<_> = "010".split("0").collect();
1057     /// assert_eq!(d, &["", "1", ""]);
1058     /// ```
1059     ///
1060     /// When the empty string is used as a separator, it separates
1061     /// every character in the string, along with the beginning
1062     /// and end of the string.
1063     ///
1064     /// ```
1065     /// let f: Vec<_> = "rust".split("").collect();
1066     /// assert_eq!(f, &["", "r", "u", "s", "t", ""]);
1067     /// ```
1068     ///
1069     /// Contiguous separators can lead to possibly surprising behavior
1070     /// when whitespace is used as the separator. This code is correct:
1071     ///
1072     /// ```
1073     /// let x = "    a  b c".to_string();
1074     /// let d: Vec<_> = x.split(' ').collect();
1075     ///
1076     /// assert_eq!(d, &["", "", "", "", "a", "", "b", "c"]);
1077     /// ```
1078     ///
1079     /// It does _not_ give you:
1080     ///
1081     /// ```,ignore
1082     /// assert_eq!(d, &["a", "b", "c"]);
1083     /// ```
1084     ///
1085     /// Use [`split_whitespace`] for this behavior.
1086     ///
1087     /// [`split_whitespace`]: #method.split_whitespace
1088     #[stable(feature = "rust1", since = "1.0.0")]
1089     #[inline]
1090     pub fn split<'a, P: Pattern<'a>>(&'a self, pat: P) -> Split<'a, P> {
1091         core_str::StrExt::split(self, pat)
1092     }
1093
1094     /// An iterator over substrings of the given string slice, separated by
1095     /// characters matched by a pattern and yielded in reverse order.
1096     ///
1097     /// The pattern can be a `&str`, [`char`], or a closure that determines the
1098     /// split.
1099     ///
1100     /// [`char`]: primitive.char.html
1101     ///
1102     /// # Iterator behavior
1103     ///
1104     /// The returned iterator requires that the pattern supports a reverse
1105     /// search, and it will be a [`DoubleEndedIterator`] if a forward/reverse
1106     /// search yields the same elements.
1107     ///
1108     /// [`DoubleEndedIterator`]: iter/trait.DoubleEndedIterator.html
1109     ///
1110     /// For iterating from the front, the [`split`] method can be used.
1111     ///
1112     /// [`split`]: #method.split
1113     ///
1114     /// # Examples
1115     ///
1116     /// Simple patterns:
1117     ///
1118     /// ```
1119     /// let v: Vec<&str> = "Mary had a little lamb".rsplit(' ').collect();
1120     /// assert_eq!(v, ["lamb", "little", "a", "had", "Mary"]);
1121     ///
1122     /// let v: Vec<&str> = "".rsplit('X').collect();
1123     /// assert_eq!(v, [""]);
1124     ///
1125     /// let v: Vec<&str> = "lionXXtigerXleopard".rsplit('X').collect();
1126     /// assert_eq!(v, ["leopard", "tiger", "", "lion"]);
1127     ///
1128     /// let v: Vec<&str> = "lion::tiger::leopard".rsplit("::").collect();
1129     /// assert_eq!(v, ["leopard", "tiger", "lion"]);
1130     /// ```
1131     ///
1132     /// A more complex pattern, using a closure:
1133     ///
1134     /// ```
1135     /// let v: Vec<&str> = "abc1defXghi".rsplit(|c| c == '1' || c == 'X').collect();
1136     /// assert_eq!(v, ["ghi", "def", "abc"]);
1137     /// ```
1138     #[stable(feature = "rust1", since = "1.0.0")]
1139     #[inline]
1140     pub fn rsplit<'a, P: Pattern<'a>>(&'a self, pat: P) -> RSplit<'a, P>
1141         where P::Searcher: ReverseSearcher<'a>
1142     {
1143         core_str::StrExt::rsplit(self, pat)
1144     }
1145
1146     /// An iterator over substrings of the given string slice, separated by
1147     /// characters matched by a pattern.
1148     ///
1149     /// The pattern can be a `&str`, [`char`], or a closure that determines the
1150     /// split.
1151     ///
1152     /// Equivalent to [`split`], except that the trailing substring
1153     /// is skipped if empty.
1154     ///
1155     /// [`split`]: #method.split
1156     ///
1157     /// This method can be used for string data that is _terminated_,
1158     /// rather than _separated_ by a pattern.
1159     ///
1160     /// # Iterator behavior
1161     ///
1162     /// The returned iterator will be a [`DoubleEndedIterator`] if the pattern
1163     /// allows a reverse search and forward/reverse search yields the same
1164     /// elements. This is true for, eg, [`char`] but not for `&str`.
1165     ///
1166     /// [`DoubleEndedIterator`]: iter/trait.DoubleEndedIterator.html
1167     /// [`char`]: primitive.char.html
1168     ///
1169     /// If the pattern allows a reverse search but its results might differ
1170     /// from a forward search, the [`rsplit_terminator`] method can be used.
1171     ///
1172     /// [`rsplit_terminator`]: #method.rsplit_terminator
1173     ///
1174     /// # Examples
1175     ///
1176     /// Basic usage:
1177     ///
1178     /// ```
1179     /// let v: Vec<&str> = "A.B.".split_terminator('.').collect();
1180     /// assert_eq!(v, ["A", "B"]);
1181     ///
1182     /// let v: Vec<&str> = "A..B..".split_terminator(".").collect();
1183     /// assert_eq!(v, ["A", "", "B", ""]);
1184     /// ```
1185     #[stable(feature = "rust1", since = "1.0.0")]
1186     #[inline]
1187     pub fn split_terminator<'a, P: Pattern<'a>>(&'a self, pat: P) -> SplitTerminator<'a, P> {
1188         core_str::StrExt::split_terminator(self, pat)
1189     }
1190
1191     /// An iterator over substrings of `self`, separated by characters
1192     /// matched by a pattern and yielded in reverse order.
1193     ///
1194     /// The pattern can be a simple `&str`, [`char`], or a closure that
1195     /// determines the split.
1196     /// Additional libraries might provide more complex patterns like
1197     /// regular expressions.
1198     ///
1199     /// [`char`]: primitive.char.html
1200     ///
1201     /// Equivalent to [`split`], except that the trailing substring is
1202     /// skipped if empty.
1203     ///
1204     /// [`split`]: #method.split
1205     ///
1206     /// This method can be used for string data that is _terminated_,
1207     /// rather than _separated_ by a pattern.
1208     ///
1209     /// # Iterator behavior
1210     ///
1211     /// The returned iterator requires that the pattern supports a
1212     /// reverse search, and it will be double ended if a forward/reverse
1213     /// search yields the same elements.
1214     ///
1215     /// For iterating from the front, the [`split_terminator`] method can be
1216     /// used.
1217     ///
1218     /// [`split_terminator`]: #method.split_terminator
1219     ///
1220     /// # Examples
1221     ///
1222     /// ```
1223     /// let v: Vec<&str> = "A.B.".rsplit_terminator('.').collect();
1224     /// assert_eq!(v, ["B", "A"]);
1225     ///
1226     /// let v: Vec<&str> = "A..B..".rsplit_terminator(".").collect();
1227     /// assert_eq!(v, ["", "B", "", "A"]);
1228     /// ```
1229     #[stable(feature = "rust1", since = "1.0.0")]
1230     #[inline]
1231     pub fn rsplit_terminator<'a, P: Pattern<'a>>(&'a self, pat: P) -> RSplitTerminator<'a, P>
1232         where P::Searcher: ReverseSearcher<'a>
1233     {
1234         core_str::StrExt::rsplit_terminator(self, pat)
1235     }
1236
1237     /// An iterator over substrings of the given string slice, separated by a
1238     /// pattern, restricted to returning at most `n` items.
1239     ///
1240     /// If `n` substrings are returned, the last substring (the `n`th substring)
1241     /// will contain the remainder of the string.
1242     ///
1243     /// The pattern can be a `&str`, [`char`], or a closure that determines the
1244     /// split.
1245     ///
1246     /// [`char`]: primitive.char.html
1247     ///
1248     /// # Iterator behavior
1249     ///
1250     /// The returned iterator will not be double ended, because it is
1251     /// not efficient to support.
1252     ///
1253     /// If the pattern allows a reverse search, the [`rsplitn`] method can be
1254     /// used.
1255     ///
1256     /// [`rsplitn`]: #method.rsplitn
1257     ///
1258     /// # Examples
1259     ///
1260     /// Simple patterns:
1261     ///
1262     /// ```
1263     /// let v: Vec<&str> = "Mary had a little lambda".splitn(3, ' ').collect();
1264     /// assert_eq!(v, ["Mary", "had", "a little lambda"]);
1265     ///
1266     /// let v: Vec<&str> = "lionXXtigerXleopard".splitn(3, "X").collect();
1267     /// assert_eq!(v, ["lion", "", "tigerXleopard"]);
1268     ///
1269     /// let v: Vec<&str> = "abcXdef".splitn(1, 'X').collect();
1270     /// assert_eq!(v, ["abcXdef"]);
1271     ///
1272     /// let v: Vec<&str> = "".splitn(1, 'X').collect();
1273     /// assert_eq!(v, [""]);
1274     /// ```
1275     ///
1276     /// A more complex pattern, using a closure:
1277     ///
1278     /// ```
1279     /// let v: Vec<&str> = "abc1defXghi".splitn(2, |c| c == '1' || c == 'X').collect();
1280     /// assert_eq!(v, ["abc", "defXghi"]);
1281     /// ```
1282     #[stable(feature = "rust1", since = "1.0.0")]
1283     #[inline]
1284     pub fn splitn<'a, P: Pattern<'a>>(&'a self, n: usize, pat: P) -> SplitN<'a, P> {
1285         core_str::StrExt::splitn(self, n, pat)
1286     }
1287
1288     /// An iterator over substrings of this string slice, separated by a
1289     /// pattern, starting from the end of the string, restricted to returning
1290     /// at most `n` items.
1291     ///
1292     /// If `n` substrings are returned, the last substring (the `n`th substring)
1293     /// will contain the remainder of the string.
1294     ///
1295     /// The pattern can be a `&str`, [`char`], or a closure that
1296     /// determines the split.
1297     ///
1298     /// [`char`]: primitive.char.html
1299     ///
1300     /// # Iterator behavior
1301     ///
1302     /// The returned iterator will not be double ended, because it is not
1303     /// efficient to support.
1304     ///
1305     /// For splitting from the front, the [`splitn`] method can be used.
1306     ///
1307     /// [`splitn`]: #method.splitn
1308     ///
1309     /// # Examples
1310     ///
1311     /// Simple patterns:
1312     ///
1313     /// ```
1314     /// let v: Vec<&str> = "Mary had a little lamb".rsplitn(3, ' ').collect();
1315     /// assert_eq!(v, ["lamb", "little", "Mary had a"]);
1316     ///
1317     /// let v: Vec<&str> = "lionXXtigerXleopard".rsplitn(3, 'X').collect();
1318     /// assert_eq!(v, ["leopard", "tiger", "lionX"]);
1319     ///
1320     /// let v: Vec<&str> = "lion::tiger::leopard".rsplitn(2, "::").collect();
1321     /// assert_eq!(v, ["leopard", "lion::tiger"]);
1322     /// ```
1323     ///
1324     /// A more complex pattern, using a closure:
1325     ///
1326     /// ```
1327     /// let v: Vec<&str> = "abc1defXghi".rsplitn(2, |c| c == '1' || c == 'X').collect();
1328     /// assert_eq!(v, ["ghi", "abc1def"]);
1329     /// ```
1330     #[stable(feature = "rust1", since = "1.0.0")]
1331     #[inline]
1332     pub fn rsplitn<'a, P: Pattern<'a>>(&'a self, n: usize, pat: P) -> RSplitN<'a, P>
1333         where P::Searcher: ReverseSearcher<'a>
1334     {
1335         core_str::StrExt::rsplitn(self, n, pat)
1336     }
1337
1338     /// An iterator over the disjoint matches of a pattern within the given string
1339     /// slice.
1340     ///
1341     /// The pattern can be a `&str`, [`char`], or a closure that
1342     /// determines if a character matches.
1343     ///
1344     /// [`char`]: primitive.char.html
1345     ///
1346     /// # Iterator behavior
1347     ///
1348     /// The returned iterator will be a [`DoubleEndedIterator`] if the pattern
1349     /// allows a reverse search and forward/reverse search yields the same
1350     /// elements. This is true for, eg, [`char`] but not for `&str`.
1351     ///
1352     /// [`DoubleEndedIterator`]: iter/trait.DoubleEndedIterator.html
1353     /// [`char`]: primitive.char.html
1354     ///
1355     /// If the pattern allows a reverse search but its results might differ
1356     /// from a forward search, the [`rmatches`] method can be used.
1357     ///
1358     /// [`rmatches`]: #method.rmatches
1359     ///
1360     /// # Examples
1361     ///
1362     /// Basic usage:
1363     ///
1364     /// ```
1365     /// let v: Vec<&str> = "abcXXXabcYYYabc".matches("abc").collect();
1366     /// assert_eq!(v, ["abc", "abc", "abc"]);
1367     ///
1368     /// let v: Vec<&str> = "1abc2abc3".matches(char::is_numeric).collect();
1369     /// assert_eq!(v, ["1", "2", "3"]);
1370     /// ```
1371     #[stable(feature = "str_matches", since = "1.2.0")]
1372     #[inline]
1373     pub fn matches<'a, P: Pattern<'a>>(&'a self, pat: P) -> Matches<'a, P> {
1374         core_str::StrExt::matches(self, pat)
1375     }
1376
1377     /// An iterator over the disjoint matches of a pattern within this string slice,
1378     /// yielded in reverse order.
1379     ///
1380     /// The pattern can be a `&str`, [`char`], or a closure that determines if
1381     /// a character matches.
1382     ///
1383     /// [`char`]: primitive.char.html
1384     ///
1385     /// # Iterator behavior
1386     ///
1387     /// The returned iterator requires that the pattern supports a reverse
1388     /// search, and it will be a [`DoubleEndedIterator`] if a forward/reverse
1389     /// search yields the same elements.
1390     ///
1391     /// [`DoubleEndedIterator`]: iter/trait.DoubleEndedIterator.html
1392     ///
1393     /// For iterating from the front, the [`matches`] method can be used.
1394     ///
1395     /// [`matches`]: #method.matches
1396     ///
1397     /// # Examples
1398     ///
1399     /// Basic usage:
1400     ///
1401     /// ```
1402     /// let v: Vec<&str> = "abcXXXabcYYYabc".rmatches("abc").collect();
1403     /// assert_eq!(v, ["abc", "abc", "abc"]);
1404     ///
1405     /// let v: Vec<&str> = "1abc2abc3".rmatches(char::is_numeric).collect();
1406     /// assert_eq!(v, ["3", "2", "1"]);
1407     /// ```
1408     #[stable(feature = "str_matches", since = "1.2.0")]
1409     #[inline]
1410     pub fn rmatches<'a, P: Pattern<'a>>(&'a self, pat: P) -> RMatches<'a, P>
1411         where P::Searcher: ReverseSearcher<'a>
1412     {
1413         core_str::StrExt::rmatches(self, pat)
1414     }
1415
1416     /// An iterator over the disjoint matches of a pattern within this string
1417     /// slice as well as the index that the match starts at.
1418     ///
1419     /// For matches of `pat` within `self` that overlap, only the indices
1420     /// corresponding to the first match are returned.
1421     ///
1422     /// The pattern can be a `&str`, [`char`], or a closure that determines
1423     /// if a character matches.
1424     ///
1425     /// [`char`]: primitive.char.html
1426     ///
1427     /// # Iterator behavior
1428     ///
1429     /// The returned iterator will be a [`DoubleEndedIterator`] if the pattern
1430     /// allows a reverse search and forward/reverse search yields the same
1431     /// elements. This is true for, eg, [`char`] but not for `&str`.
1432     ///
1433     /// [`DoubleEndedIterator`]: iter/trait.DoubleEndedIterator.html
1434     ///
1435     /// If the pattern allows a reverse search but its results might differ
1436     /// from a forward search, the [`rmatch_indices`] method can be used.
1437     ///
1438     /// [`rmatch_indices`]: #method.rmatch_indices
1439     ///
1440     /// # Examples
1441     ///
1442     /// Basic usage:
1443     ///
1444     /// ```
1445     /// let v: Vec<_> = "abcXXXabcYYYabc".match_indices("abc").collect();
1446     /// assert_eq!(v, [(0, "abc"), (6, "abc"), (12, "abc")]);
1447     ///
1448     /// let v: Vec<_> = "1abcabc2".match_indices("abc").collect();
1449     /// assert_eq!(v, [(1, "abc"), (4, "abc")]);
1450     ///
1451     /// let v: Vec<_> = "ababa".match_indices("aba").collect();
1452     /// assert_eq!(v, [(0, "aba")]); // only the first `aba`
1453     /// ```
1454     #[stable(feature = "str_match_indices", since = "1.5.0")]
1455     #[inline]
1456     pub fn match_indices<'a, P: Pattern<'a>>(&'a self, pat: P) -> MatchIndices<'a, P> {
1457         core_str::StrExt::match_indices(self, pat)
1458     }
1459
1460     /// An iterator over the disjoint matches of a pattern within `self`,
1461     /// yielded in reverse order along with the index of the match.
1462     ///
1463     /// For matches of `pat` within `self` that overlap, only the indices
1464     /// corresponding to the last match are returned.
1465     ///
1466     /// The pattern can be a `&str`, [`char`], or a closure that determines if a
1467     /// character matches.
1468     ///
1469     /// [`char`]: primitive.char.html
1470     ///
1471     /// # Iterator behavior
1472     ///
1473     /// The returned iterator requires that the pattern supports a reverse
1474     /// search, and it will be a [`DoubleEndedIterator`] if a forward/reverse
1475     /// search yields the same elements.
1476     ///
1477     /// [`DoubleEndedIterator`]: iter/trait.DoubleEndedIterator.html
1478     ///
1479     /// For iterating from the front, the [`match_indices`] method can be used.
1480     ///
1481     /// [`match_indices`]: #method.match_indices
1482     ///
1483     /// # Examples
1484     ///
1485     /// Basic usage:
1486     ///
1487     /// ```
1488     /// let v: Vec<_> = "abcXXXabcYYYabc".rmatch_indices("abc").collect();
1489     /// assert_eq!(v, [(12, "abc"), (6, "abc"), (0, "abc")]);
1490     ///
1491     /// let v: Vec<_> = "1abcabc2".rmatch_indices("abc").collect();
1492     /// assert_eq!(v, [(4, "abc"), (1, "abc")]);
1493     ///
1494     /// let v: Vec<_> = "ababa".rmatch_indices("aba").collect();
1495     /// assert_eq!(v, [(2, "aba")]); // only the last `aba`
1496     /// ```
1497     #[stable(feature = "str_match_indices", since = "1.5.0")]
1498     #[inline]
1499     pub fn rmatch_indices<'a, P: Pattern<'a>>(&'a self, pat: P) -> RMatchIndices<'a, P>
1500         where P::Searcher: ReverseSearcher<'a>
1501     {
1502         core_str::StrExt::rmatch_indices(self, pat)
1503     }
1504
1505     /// Returns a string slice with leading and trailing whitespace removed.
1506     ///
1507     /// 'Whitespace' is defined according to the terms of the Unicode Derived
1508     /// Core Property `White_Space`.
1509     ///
1510     /// # Examples
1511     ///
1512     /// Basic usage:
1513     ///
1514     /// ```
1515     /// let s = " Hello\tworld\t";
1516     ///
1517     /// assert_eq!("Hello\tworld", s.trim());
1518     /// ```
1519     #[stable(feature = "rust1", since = "1.0.0")]
1520     pub fn trim(&self) -> &str {
1521         UnicodeStr::trim(self)
1522     }
1523
1524     /// Returns a string slice with leading whitespace removed.
1525     ///
1526     /// 'Whitespace' is defined according to the terms of the Unicode Derived
1527     /// Core Property `White_Space`.
1528     ///
1529     /// # Text directionality
1530     ///
1531     /// A string is a sequence of bytes. 'Left' in this context means the first
1532     /// position of that byte string; for a language like Arabic or Hebrew
1533     /// which are 'right to left' rather than 'left to right', this will be
1534     /// the _right_ side, not the left.
1535     ///
1536     /// # Examples
1537     ///
1538     /// Basic usage:
1539     ///
1540     /// ```
1541     /// let s = " Hello\tworld\t";
1542     ///
1543     /// assert_eq!("Hello\tworld\t", s.trim_left());
1544     /// ```
1545     ///
1546     /// Directionality:
1547     ///
1548     /// ```
1549     /// let s = "  English";
1550     /// assert!(Some('E') == s.trim_left().chars().next());
1551     ///
1552     /// let s = "  עברית";
1553     /// assert!(Some('ע') == s.trim_left().chars().next());
1554     /// ```
1555     #[stable(feature = "rust1", since = "1.0.0")]
1556     pub fn trim_left(&self) -> &str {
1557         UnicodeStr::trim_left(self)
1558     }
1559
1560     /// Returns a string slice with trailing whitespace removed.
1561     ///
1562     /// 'Whitespace' is defined according to the terms of the Unicode Derived
1563     /// Core Property `White_Space`.
1564     ///
1565     /// # Text directionality
1566     ///
1567     /// A string is a sequence of bytes. 'Right' in this context means the last
1568     /// position of that byte string; for a language like Arabic or Hebrew
1569     /// which are 'right to left' rather than 'left to right', this will be
1570     /// the _left_ side, not the right.
1571     ///
1572     /// # Examples
1573     ///
1574     /// Basic usage:
1575     ///
1576     /// ```
1577     /// let s = " Hello\tworld\t";
1578     ///
1579     /// assert_eq!(" Hello\tworld", s.trim_right());
1580     /// ```
1581     ///
1582     /// Directionality:
1583     ///
1584     /// ```
1585     /// let s = "English  ";
1586     /// assert!(Some('h') == s.trim_right().chars().rev().next());
1587     ///
1588     /// let s = "עברית  ";
1589     /// assert!(Some('ת') == s.trim_right().chars().rev().next());
1590     /// ```
1591     #[stable(feature = "rust1", since = "1.0.0")]
1592     pub fn trim_right(&self) -> &str {
1593         UnicodeStr::trim_right(self)
1594     }
1595
1596     /// Returns a string slice with all prefixes and suffixes that match a
1597     /// pattern repeatedly removed.
1598     ///
1599     /// The pattern can be a [`char`] or a closure that determines if a
1600     /// character matches.
1601     ///
1602     /// [`char`]: primitive.char.html
1603     ///
1604     /// # Examples
1605     ///
1606     /// Simple patterns:
1607     ///
1608     /// ```
1609     /// assert_eq!("11foo1bar11".trim_matches('1'), "foo1bar");
1610     /// assert_eq!("123foo1bar123".trim_matches(char::is_numeric), "foo1bar");
1611     ///
1612     /// let x: &[_] = &['1', '2'];
1613     /// assert_eq!("12foo1bar12".trim_matches(x), "foo1bar");
1614     /// ```
1615     ///
1616     /// A more complex pattern, using a closure:
1617     ///
1618     /// ```
1619     /// assert_eq!("1foo1barXX".trim_matches(|c| c == '1' || c == 'X'), "foo1bar");
1620     /// ```
1621     #[stable(feature = "rust1", since = "1.0.0")]
1622     pub fn trim_matches<'a, P: Pattern<'a>>(&'a self, pat: P) -> &'a str
1623         where P::Searcher: DoubleEndedSearcher<'a>
1624     {
1625         core_str::StrExt::trim_matches(self, pat)
1626     }
1627
1628     /// Returns a string slice with all prefixes that match a pattern
1629     /// repeatedly removed.
1630     ///
1631     /// The pattern can be a `&str`, [`char`], or a closure that determines if
1632     /// a character matches.
1633     ///
1634     /// [`char`]: primitive.char.html
1635     ///
1636     /// # Text directionality
1637     ///
1638     /// A string is a sequence of bytes. 'Left' in this context means the first
1639     /// position of that byte string; for a language like Arabic or Hebrew
1640     /// which are 'right to left' rather than 'left to right', this will be
1641     /// the _right_ side, not the left.
1642     ///
1643     /// # Examples
1644     ///
1645     /// Basic usage:
1646     ///
1647     /// ```
1648     /// assert_eq!("11foo1bar11".trim_left_matches('1'), "foo1bar11");
1649     /// assert_eq!("123foo1bar123".trim_left_matches(char::is_numeric), "foo1bar123");
1650     ///
1651     /// let x: &[_] = &['1', '2'];
1652     /// assert_eq!("12foo1bar12".trim_left_matches(x), "foo1bar12");
1653     /// ```
1654     #[stable(feature = "rust1", since = "1.0.0")]
1655     pub fn trim_left_matches<'a, P: Pattern<'a>>(&'a self, pat: P) -> &'a str {
1656         core_str::StrExt::trim_left_matches(self, pat)
1657     }
1658
1659     /// Returns a string slice with all suffixes that match a pattern
1660     /// repeatedly removed.
1661     ///
1662     /// The pattern can be a `&str`, [`char`], or a closure that
1663     /// determines if a character matches.
1664     ///
1665     /// [`char`]: primitive.char.html
1666     ///
1667     /// # Text directionality
1668     ///
1669     /// A string is a sequence of bytes. 'Right' in this context means the last
1670     /// position of that byte string; for a language like Arabic or Hebrew
1671     /// which are 'right to left' rather than 'left to right', this will be
1672     /// the _left_ side, not the right.
1673     ///
1674     /// # Examples
1675     ///
1676     /// Simple patterns:
1677     ///
1678     /// ```
1679     /// assert_eq!("11foo1bar11".trim_right_matches('1'), "11foo1bar");
1680     /// assert_eq!("123foo1bar123".trim_right_matches(char::is_numeric), "123foo1bar");
1681     ///
1682     /// let x: &[_] = &['1', '2'];
1683     /// assert_eq!("12foo1bar12".trim_right_matches(x), "12foo1bar");
1684     /// ```
1685     ///
1686     /// A more complex pattern, using a closure:
1687     ///
1688     /// ```
1689     /// assert_eq!("1fooX".trim_left_matches(|c| c == '1' || c == 'X'), "fooX");
1690     /// ```
1691     #[stable(feature = "rust1", since = "1.0.0")]
1692     pub fn trim_right_matches<'a, P: Pattern<'a>>(&'a self, pat: P) -> &'a str
1693         where P::Searcher: ReverseSearcher<'a>
1694     {
1695         core_str::StrExt::trim_right_matches(self, pat)
1696     }
1697
1698     /// Parses this string slice into another type.
1699     ///
1700     /// Because `parse` is so general, it can cause problems with type
1701     /// inference. As such, `parse` is one of the few times you'll see
1702     /// the syntax affectionately known as the 'turbofish': `::<>`. This
1703     /// helps the inference algorithm understand specifically which type
1704     /// you're trying to parse into.
1705     ///
1706     /// `parse` can parse any type that implements the [`FromStr`] trait.
1707     ///
1708     /// [`FromStr`]: str/trait.FromStr.html
1709     ///
1710     /// # Errors
1711     ///
1712     /// Will return [`Err`] if it's not possible to parse this string slice into
1713     /// the desired type.
1714     ///
1715     /// [`Err`]: str/trait.FromStr.html#associatedtype.Err
1716     ///
1717     /// # Examples
1718     ///
1719     /// Basic usage
1720     ///
1721     /// ```
1722     /// let four: u32 = "4".parse().unwrap();
1723     ///
1724     /// assert_eq!(4, four);
1725     /// ```
1726     ///
1727     /// Using the 'turbofish' instead of annotating `four`:
1728     ///
1729     /// ```
1730     /// let four = "4".parse::<u32>();
1731     ///
1732     /// assert_eq!(Ok(4), four);
1733     /// ```
1734     ///
1735     /// Failing to parse:
1736     ///
1737     /// ```
1738     /// let nope = "j".parse::<u32>();
1739     ///
1740     /// assert!(nope.is_err());
1741     /// ```
1742     #[inline]
1743     #[stable(feature = "rust1", since = "1.0.0")]
1744     pub fn parse<F: FromStr>(&self) -> Result<F, F::Err> {
1745         core_str::StrExt::parse(self)
1746     }
1747
1748     /// Converts a `Box<str>` into a `Box<[u8]>` without copying or allocating.
1749     #[stable(feature = "str_box_extras", since = "1.20.0")]
1750     pub fn into_boxed_bytes(self: Box<str>) -> Box<[u8]> {
1751         self.into()
1752     }
1753
1754     /// Replaces all matches of a pattern with another string.
1755     ///
1756     /// `replace` creates a new [`String`], and copies the data from this string slice into it.
1757     /// While doing so, it attempts to find matches of a pattern. If it finds any, it
1758     /// replaces them with the replacement string slice.
1759     ///
1760     /// [`String`]: string/struct.String.html
1761     ///
1762     /// # Examples
1763     ///
1764     /// Basic usage:
1765     ///
1766     /// ```
1767     /// let s = "this is old";
1768     ///
1769     /// assert_eq!("this is new", s.replace("old", "new"));
1770     /// ```
1771     ///
1772     /// When the pattern doesn't match:
1773     ///
1774     /// ```
1775     /// let s = "this is old";
1776     /// assert_eq!(s, s.replace("cookie monster", "little lamb"));
1777     /// ```
1778     #[stable(feature = "rust1", since = "1.0.0")]
1779     #[inline]
1780     pub fn replace<'a, P: Pattern<'a>>(&'a self, from: P, to: &str) -> String {
1781         let mut result = String::new();
1782         let mut last_end = 0;
1783         for (start, part) in self.match_indices(from) {
1784             result.push_str(unsafe { self.slice_unchecked(last_end, start) });
1785             result.push_str(to);
1786             last_end = start + part.len();
1787         }
1788         result.push_str(unsafe { self.slice_unchecked(last_end, self.len()) });
1789         result
1790     }
1791
1792     /// Replaces first N matches of a pattern with another string.
1793     ///
1794     /// `replacen` creates a new [`String`], and copies the data from this string slice into it.
1795     /// While doing so, it attempts to find matches of a pattern. If it finds any, it
1796     /// replaces them with the replacement string slice at most `count` times.
1797     ///
1798     /// [`String`]: string/struct.String.html
1799     ///
1800     /// # Examples
1801     ///
1802     /// Basic usage:
1803     ///
1804     /// ```
1805     /// let s = "foo foo 123 foo";
1806     /// assert_eq!("new new 123 foo", s.replacen("foo", "new", 2));
1807     /// assert_eq!("faa fao 123 foo", s.replacen('o', "a", 3));
1808     /// assert_eq!("foo foo new23 foo", s.replacen(char::is_numeric, "new", 1));
1809     /// ```
1810     ///
1811     /// When the pattern doesn't match:
1812     ///
1813     /// ```
1814     /// let s = "this is old";
1815     /// assert_eq!(s, s.replacen("cookie monster", "little lamb", 10));
1816     /// ```
1817     #[stable(feature = "str_replacen", since = "1.16.0")]
1818     pub fn replacen<'a, P: Pattern<'a>>(&'a self, pat: P, to: &str, count: usize) -> String {
1819         // Hope to reduce the times of re-allocation
1820         let mut result = String::with_capacity(32);
1821         let mut last_end = 0;
1822         for (start, part) in self.match_indices(pat).take(count) {
1823             result.push_str(unsafe { self.slice_unchecked(last_end, start) });
1824             result.push_str(to);
1825             last_end = start + part.len();
1826         }
1827         result.push_str(unsafe { self.slice_unchecked(last_end, self.len()) });
1828         result
1829     }
1830
1831     /// Returns the lowercase equivalent of this string slice, as a new [`String`].
1832     ///
1833     /// 'Lowercase' is defined according to the terms of the Unicode Derived Core Property
1834     /// `Lowercase`.
1835     ///
1836     /// Since some characters can expand into multiple characters when changing
1837     /// the case, this function returns a [`String`] instead of modifying the
1838     /// parameter in-place.
1839     ///
1840     /// [`String`]: string/struct.String.html
1841     ///
1842     /// # Examples
1843     ///
1844     /// Basic usage:
1845     ///
1846     /// ```
1847     /// let s = "HELLO";
1848     ///
1849     /// assert_eq!("hello", s.to_lowercase());
1850     /// ```
1851     ///
1852     /// A tricky example, with sigma:
1853     ///
1854     /// ```
1855     /// let sigma = "Σ";
1856     ///
1857     /// assert_eq!("σ", sigma.to_lowercase());
1858     ///
1859     /// // but at the end of a word, it's ς, not σ:
1860     /// let odysseus = "ὈΔΥΣΣΕΎΣ";
1861     ///
1862     /// assert_eq!("ὀδυσσεύς", odysseus.to_lowercase());
1863     /// ```
1864     ///
1865     /// Languages without case are not changed:
1866     ///
1867     /// ```
1868     /// let new_year = "农历新年";
1869     ///
1870     /// assert_eq!(new_year, new_year.to_lowercase());
1871     /// ```
1872     #[stable(feature = "unicode_case_mapping", since = "1.2.0")]
1873     pub fn to_lowercase(&self) -> String {
1874         let mut s = String::with_capacity(self.len());
1875         for (i, c) in self[..].char_indices() {
1876             if c == 'Σ' {
1877                 // Σ maps to σ, except at the end of a word where it maps to ς.
1878                 // This is the only conditional (contextual) but language-independent mapping
1879                 // in `SpecialCasing.txt`,
1880                 // so hard-code it rather than have a generic "condition" mechanism.
1881                 // See https://github.com/rust-lang/rust/issues/26035
1882                 map_uppercase_sigma(self, i, &mut s)
1883             } else {
1884                 s.extend(c.to_lowercase());
1885             }
1886         }
1887         return s;
1888
1889         fn map_uppercase_sigma(from: &str, i: usize, to: &mut String) {
1890             // See http://www.unicode.org/versions/Unicode7.0.0/ch03.pdf#G33992
1891             // for the definition of `Final_Sigma`.
1892             debug_assert!('Σ'.len_utf8() == 2);
1893             let is_word_final = case_ignoreable_then_cased(from[..i].chars().rev()) &&
1894                                 !case_ignoreable_then_cased(from[i + 2..].chars());
1895             to.push_str(if is_word_final { "ς" } else { "σ" });
1896         }
1897
1898         fn case_ignoreable_then_cased<I: Iterator<Item = char>>(iter: I) -> bool {
1899             use std_unicode::derived_property::{Cased, Case_Ignorable};
1900             match iter.skip_while(|&c| Case_Ignorable(c)).next() {
1901                 Some(c) => Cased(c),
1902                 None => false,
1903             }
1904         }
1905     }
1906
1907     /// Returns the uppercase equivalent of this string slice, as a new [`String`].
1908     ///
1909     /// 'Uppercase' is defined according to the terms of the Unicode Derived Core Property
1910     /// `Uppercase`.
1911     ///
1912     /// Since some characters can expand into multiple characters when changing
1913     /// the case, this function returns a [`String`] instead of modifying the
1914     /// parameter in-place.
1915     ///
1916     /// [`String`]: string/struct.String.html
1917     ///
1918     /// # Examples
1919     ///
1920     /// Basic usage:
1921     ///
1922     /// ```
1923     /// let s = "hello";
1924     ///
1925     /// assert_eq!("HELLO", s.to_uppercase());
1926     /// ```
1927     ///
1928     /// Scripts without case are not changed:
1929     ///
1930     /// ```
1931     /// let new_year = "农历新年";
1932     ///
1933     /// assert_eq!(new_year, new_year.to_uppercase());
1934     /// ```
1935     #[stable(feature = "unicode_case_mapping", since = "1.2.0")]
1936     pub fn to_uppercase(&self) -> String {
1937         let mut s = String::with_capacity(self.len());
1938         s.extend(self.chars().flat_map(|c| c.to_uppercase()));
1939         return s;
1940     }
1941
1942     /// Escapes each char in `s` with [`char::escape_debug`].
1943     ///
1944     /// [`char::escape_debug`]: primitive.char.html#method.escape_debug
1945     #[unstable(feature = "str_escape",
1946                reason = "return type may change to be an iterator",
1947                issue = "27791")]
1948     pub fn escape_debug(&self) -> String {
1949         self.chars().flat_map(|c| c.escape_debug()).collect()
1950     }
1951
1952     /// Escapes each char in `s` with [`char::escape_default`].
1953     ///
1954     /// [`char::escape_default`]: primitive.char.html#method.escape_default
1955     #[unstable(feature = "str_escape",
1956                reason = "return type may change to be an iterator",
1957                issue = "27791")]
1958     pub fn escape_default(&self) -> String {
1959         self.chars().flat_map(|c| c.escape_default()).collect()
1960     }
1961
1962     /// Escapes each char in `s` with [`char::escape_unicode`].
1963     ///
1964     /// [`char::escape_unicode`]: primitive.char.html#method.escape_unicode
1965     #[unstable(feature = "str_escape",
1966                reason = "return type may change to be an iterator",
1967                issue = "27791")]
1968     pub fn escape_unicode(&self) -> String {
1969         self.chars().flat_map(|c| c.escape_unicode()).collect()
1970     }
1971
1972     /// Converts a [`Box<str>`] into a [`String`] without copying or allocating.
1973     ///
1974     /// [`String`]: string/struct.String.html
1975     /// [`Box<str>`]: boxed/struct.Box.html
1976     ///
1977     /// # Examples
1978     ///
1979     /// Basic usage:
1980     ///
1981     /// ```
1982     /// let string = String::from("birthday gift");
1983     /// let boxed_str = string.clone().into_boxed_str();
1984     ///
1985     /// assert_eq!(boxed_str.into_string(), string);
1986     /// ```
1987     #[stable(feature = "box_str", since = "1.4.0")]
1988     pub fn into_string(self: Box<str>) -> String {
1989         unsafe {
1990             let slice = mem::transmute::<Box<str>, Box<[u8]>>(self);
1991             String::from_utf8_unchecked(slice.into_vec())
1992         }
1993     }
1994
1995     /// Create a [`String`] by repeating a string `n` times.
1996     ///
1997     /// [`String`]: string/struct.String.html
1998     ///
1999     /// # Examples
2000     ///
2001     /// Basic usage:
2002     ///
2003     /// ```
2004     /// assert_eq!("abc".repeat(4), String::from("abcabcabcabc"));
2005     /// ```
2006     #[stable(feature = "repeat_str", since = "1.16.0")]
2007     pub fn repeat(&self, n: usize) -> String {
2008         let mut s = String::with_capacity(self.len() * n);
2009         s.extend((0..n).map(|_| self));
2010         s
2011     }
2012 }
2013
2014 /// Converts a boxed slice of bytes to a boxed string slice without checking
2015 /// that the string contains valid UTF-8.
2016 #[stable(feature = "str_box_extras", since = "1.20.0")]
2017 pub unsafe fn from_boxed_utf8_unchecked(v: Box<[u8]>) -> Box<str> {
2018     mem::transmute(v)
2019 }