src/liballoc/string.rs

   1 // Copyright 2014 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 //! A UTF-8 encoded, growable string.
  12 //!
  13 //! This module contains the [`String`] type, a trait for converting
  14 //! [`ToString`]s, and several error types that may result from working with
  15 //! [`String`]s.
  16 //!
  17 //! [`ToString`]: trait.ToString.html
  18 //!
  19 //! # Examples
  20 //!
  21 //! There are multiple ways to create a new [`String`] from a string literal:
  22 //!
  23 //! ```
  24 //! let s = "Hello".to_string();
  25 //!
  26 //! let s = String::from("world");
  27 //! let s: String = "also this".into();
  28 //! ```
  29 //!
  30 //! You can create a new [`String`] from an existing one by concatenating with
  31 //! `+`:
  32 //!
  33 //! [`String`]: struct.String.html
  34 //!
  35 //! ```
  36 //! let s = "Hello".to_string();
  37 //!
  38 //! let message = s + " world!";
  39 //! ```
  40 //!
  41 //! If you have a vector of valid UTF-8 bytes, you can make a [`String`] out of
  42 //! it. You can do the reverse too.
  43 //!
  44 //! ```
  45 //! let sparkle_heart = vec![240, 159, 146, 150];
  46 //!
  47 //! // We know these bytes are valid, so we'll use `unwrap()`.
  48 //! let sparkle_heart = String::from_utf8(sparkle_heart).unwrap();
  49 //!
  50 //! assert_eq!("💖", sparkle_heart);
  51 //!
  52 //! let bytes = sparkle_heart.into_bytes();
  53 //!
  54 //! assert_eq!(bytes, [240, 159, 146, 150]);
  55 //! ```
  56
  57 #![stable(feature = "rust1", since = "1.0.0")]
  58
  59 use core::fmt;
  60 use core::hash;
  61 use core::iter::{FromIterator, FusedIterator};
  62 use core::ops::{self, Add, AddAssign, Index, IndexMut};
  63 use core::ptr;
  64 use core::str::pattern::Pattern;
  65 use std_unicode::lossy;
  66 use std_unicode::char::{decode_utf16, REPLACEMENT_CHARACTER};
  67
  68 use borrow::{Cow, ToOwned};
  69 use range::RangeArgument;
  70 use Bound::{Excluded, Included, Unbounded};
  71 use str::{self, from_boxed_utf8_unchecked, FromStr, Utf8Error, Chars};
  72 use vec::Vec;
  73 use boxed::Box;
  74
  75 /// A UTF-8 encoded, growable string.
  76 ///
  77 /// The `String` type is the most common string type that has ownership over the
  78 /// contents of the string. It has a close relationship with its borrowed
  79 /// counterpart, the primitive [`str`].
  80 ///
  81 /// [`str`]: ../../std/primitive.str.html
  82 ///
  83 /// # Examples
  84 ///
  85 /// You can create a `String` from a literal string with [`String::from`]:
  86 ///
  87 /// ```
  88 /// let hello = String::from("Hello, world!");
  89 /// ```
  90 ///
  91 /// You can append a [`char`] to a `String` with the [`push`] method, and
  92 /// append a [`&str`] with the [`push_str`] method:
  93 ///
  94 /// ```
  95 /// let mut hello = String::from("Hello, ");
  96 ///
  97 /// hello.push('w');
  98 /// hello.push_str("orld!");
  99 /// ```
 100 ///
 101 /// [`String::from`]: #method.from
 102 /// [`char`]: ../../std/primitive.char.html
 103 /// [`push`]: #method.push
 104 /// [`push_str`]: #method.push_str
 105 ///
 106 /// If you have a vector of UTF-8 bytes, you can create a `String` from it with
 107 /// the [`from_utf8`] method:
 108 ///
 109 /// ```
 110 /// // some bytes, in a vector
 111 /// let sparkle_heart = vec![240, 159, 146, 150];
 112 ///
 113 /// // We know these bytes are valid, so we'll use `unwrap()`.
 114 /// let sparkle_heart = String::from_utf8(sparkle_heart).unwrap();
 115 ///
 116 /// assert_eq!("💖", sparkle_heart);
 117 /// ```
 118 ///
 119 /// [`from_utf8`]: #method.from_utf8
 120 ///
 121 /// # UTF-8
 122 ///
 123 /// `String`s are always valid UTF-8. This has a few implications, the first of
 124 /// which is that if you need a non-UTF-8 string, consider [`OsString`]. It is
 125 /// similar, but without the UTF-8 constraint. The second implication is that
 126 /// you cannot index into a `String`:
 127 ///
 128 /// ```compile_fail,E0277
 129 /// let s = "hello";
 130 ///
 131 /// println!("The first letter of s is {}", s[0]); // ERROR!!!
 132 /// ```
 133 ///
 134 /// [`OsString`]: ../../std/ffi/struct.OsString.html
 135 ///
 136 /// Indexing is intended to be a constant-time operation, but UTF-8 encoding
 137 /// does not allow us to do this. Furthermore, it's not clear what sort of
 138 /// thing the index should return: a byte, a codepoint, or a grapheme cluster.
 139 /// The [`bytes`] and [`chars`] methods return iterators over the first
 140 /// two, respectively.
 141 ///
 142 /// [`bytes`]: #method.bytes
 143 /// [`chars`]: #method.chars
 144 ///
 145 /// # Deref
 146 ///
 147 /// `String`s implement [`Deref`]`<Target=str>`, and so inherit all of [`str`]'s
 148 /// methods. In addition, this means that you can pass a `String` to a
 149 /// function which takes a [`&str`] by using an ampersand (`&`):
 150 ///
 151 /// ```
 152 /// fn takes_str(s: &str) { }
 153 ///
 154 /// let s = String::from("Hello");
 155 ///
 156 /// takes_str(&s);
 157 /// ```
 158 ///
 159 /// This will create a [`&str`] from the `String` and pass it in. This
 160 /// conversion is very inexpensive, and so generally, functions will accept
 161 /// [`&str`]s as arguments unless they need a `String` for some specific
 162 /// reason.
 163 ///
 164 /// In certain cases Rust doesn't have enough information to make this
 165 /// conversion, known as [`Deref`] coercion. In the following example a string
 166 /// slice [`&'a str`][`&str`] implements the trait `TraitExample`, and the function
 167 /// `example_func` takes anything that implements the trait. In this case Rust
 168 /// would need to make two implicit conversions, which Rust doesn't have the
 169 /// means to do. For that reason, the following example will not compile.
 170 ///
 171 /// ```compile_fail,E0277
 172 /// trait TraitExample {}
 173 ///
 174 /// impl<'a> TraitExample for &'a str {}
 175 ///
 176 /// fn example_func<A: TraitExample>(example_arg: A) {}
 177 ///
 178 /// fn main() {
 179 ///     let example_string = String::from("example_string");
 180 ///     example_func(&example_string);
 181 /// }
 182 /// ```
 183 ///
 184 /// There are two options that would work instead. The first would be to
 185 /// change the line `example_func(&example_string);` to
 186 /// `example_func(example_string.as_str());`, using the method [`as_str()`]
 187 /// to explicitly extract the string slice containing the string. The second
 188 /// way changes `example_func(&example_string);` to
 189 /// `example_func(&*example_string);`. In this case we are dereferencing a
 190 /// `String` to a [`str`][`&str`], then referencing the [`str`][`&str`] back to
 191 /// [`&str`]. The second way is more idiomatic, however both work to do the
 192 /// conversion explicitly rather than relying on the implicit conversion.
 193 ///
 194 /// # Representation
 195 ///
 196 /// A `String` is made up of three components: a pointer to some bytes, a
 197 /// length, and a capacity. The pointer points to an internal buffer `String`
 198 /// uses to store its data. The length is the number of bytes currently stored
 199 /// in the buffer, and the capacity is the size of the buffer in bytes. As such,
 200 /// the length will always be less than or equal to the capacity.
 201 ///
 202 /// This buffer is always stored on the heap.
 203 ///
 204 /// You can look at these with the [`as_ptr`], [`len`], and [`capacity`]
 205 /// methods:
 206 ///
 207 /// ```
 208 /// use std::mem;
 209 ///
 210 /// let story = String::from("Once upon a time...");
 211 ///
 212 /// let ptr = story.as_ptr();
 213 /// let len = story.len();
 214 /// let capacity = story.capacity();
 215 ///
 216 /// // story has nineteen bytes
 217 /// assert_eq!(19, len);
 218 ///
 219 /// // Now that we have our parts, we throw the story away.
 220 /// mem::forget(story);
 221 ///
 222 /// // We can re-build a String out of ptr, len, and capacity. This is all
 223 /// // unsafe because we are responsible for making sure the components are
 224 /// // valid:
 225 /// let s = unsafe { String::from_raw_parts(ptr as *mut _, len, capacity) } ;
 226 ///
 227 /// assert_eq!(String::from("Once upon a time..."), s);
 228 /// ```
 229 ///
 230 /// [`as_ptr`]: #method.as_ptr
 231 /// [`len`]: #method.len
 232 /// [`capacity`]: #method.capacity
 233 ///
 234 /// If a `String` has enough capacity, adding elements to it will not
 235 /// re-allocate. For example, consider this program:
 236 ///
 237 /// ```
 238 /// let mut s = String::new();
 239 ///
 240 /// println!("{}", s.capacity());
 241 ///
 242 /// for _ in 0..5 {
 243 ///     s.push_str("hello");
 244 ///     println!("{}", s.capacity());
 245 /// }
 246 /// ```
 247 ///
 248 /// This will output the following:
 249 ///
 250 /// ```text
 251 /// 0
 252 /// 5
 253 /// 10
 254 /// 20
 255 /// 20
 256 /// 40
 257 /// ```
 258 ///
 259 /// At first, we have no memory allocated at all, but as we append to the
 260 /// string, it increases its capacity appropriately. If we instead use the
 261 /// [`with_capacity`] method to allocate the correct capacity initially:
 262 ///
 263 /// ```
 264 /// let mut s = String::with_capacity(25);
 265 ///
 266 /// println!("{}", s.capacity());
 267 ///
 268 /// for _ in 0..5 {
 269 ///     s.push_str("hello");
 270 ///     println!("{}", s.capacity());
 271 /// }
 272 /// ```
 273 ///
 274 /// [`with_capacity`]: #method.with_capacity
 275 ///
 276 /// We end up with a different output:
 277 ///
 278 /// ```text
 279 /// 25
 280 /// 25
 281 /// 25
 282 /// 25
 283 /// 25
 284 /// 25
 285 /// ```
 286 ///
 287 /// Here, there's no need to allocate more memory inside the loop.
 288 ///
 289 /// [`&str`]: ../../std/primitive.str.html
 290 /// [`Deref`]: ../../std/ops/trait.Deref.html
 291 /// [`as_str()`]: struct.String.html#method.as_str
 292 #[derive(PartialOrd, Eq, Ord)]
 293 #[stable(feature = "rust1", since = "1.0.0")]
 294 pub struct String {
 295     vec: Vec<u8>,
 296 }
 297
 298 /// A possible error value when converting a `String` from a UTF-8 byte vector.
 299 ///
 300 /// This type is the error type for the [`from_utf8`] method on [`String`]. It
 301 /// is designed in such a way to carefully avoid reallocations: the
 302 /// [`into_bytes`] method will give back the byte vector that was used in the
 303 /// conversion attempt.
 304 ///
 305 /// [`from_utf8`]: struct.String.html#method.from_utf8
 306 /// [`String`]: struct.String.html
 307 /// [`into_bytes`]: struct.FromUtf8Error.html#method.into_bytes
 308 ///
 309 /// The [`Utf8Error`] type provided by [`std::str`] represents an error that may
 310 /// occur when converting a slice of [`u8`]s to a [`&str`]. In this sense, it's
 311 /// an analogue to `FromUtf8Error`, and you can get one from a `FromUtf8Error`
 312 /// through the [`utf8_error`] method.
 313 ///
 314 /// [`Utf8Error`]: ../../std/str/struct.Utf8Error.html
 315 /// [`std::str`]: ../../std/str/index.html
 316 /// [`u8`]: ../../std/primitive.u8.html
 317 /// [`&str`]: ../../std/primitive.str.html
 318 /// [`utf8_error`]: #method.utf8_error
 319 ///
 320 /// # Examples
 321 ///
 322 /// Basic usage:
 323 ///
 324 /// ```
 325 /// // some invalid bytes, in a vector
 326 /// let bytes = vec![0, 159];
 327 ///
 328 /// let value = String::from_utf8(bytes);
 329 ///
 330 /// assert!(value.is_err());
 331 /// assert_eq!(vec![0, 159], value.unwrap_err().into_bytes());
 332 /// ```
 333 #[stable(feature = "rust1", since = "1.0.0")]
 334 #[derive(Debug)]
 335 pub struct FromUtf8Error {
 336     bytes: Vec<u8>,
 337     error: Utf8Error,
 338 }
 339
 340 /// A possible error value when converting a `String` from a UTF-16 byte slice.
 341 ///
 342 /// This type is the error type for the [`from_utf16`] method on [`String`].
 343 ///
 344 /// [`from_utf16`]: struct.String.html#method.from_utf16
 345 /// [`String`]: struct.String.html
 346 ///
 347 /// # Examples
 348 ///
 349 /// Basic usage:
 350 ///
 351 /// ```
 352 /// // 𝄞mu<invalid>ic
 353 /// let v = &[0xD834, 0xDD1E, 0x006d, 0x0075,
 354 ///           0xD800, 0x0069, 0x0063];
 355 ///
 356 /// assert!(String::from_utf16(v).is_err());
 357 /// ```
 358 #[stable(feature = "rust1", since = "1.0.0")]
 359 #[derive(Debug)]
 360 pub struct FromUtf16Error(());
 361
 362 impl String {
 363     /// Creates a new empty `String`.
 364     ///
 365     /// Given that the `String` is empty, this will not allocate any initial
 366     /// buffer. While that means that this initial operation is very
 367     /// inexpensive, but may cause excessive allocation later, when you add
 368     /// data. If you have an idea of how much data the `String` will hold,
 369     /// consider the [`with_capacity`] method to prevent excessive
 370     /// re-allocation.
 371     ///
 372     /// [`with_capacity`]: #method.with_capacity
 373     ///
 374     /// # Examples
 375     ///
 376     /// Basic usage:
 377     ///
 378     /// ```
 379     /// let s = String::new();
 380     /// ```
 381     #[inline]
 382     #[stable(feature = "rust1", since = "1.0.0")]
 383     pub fn new() -> String {
 384         String { vec: Vec::new() }
 385     }
 386
 387     /// Creates a new empty `String` with a particular capacity.
 388     ///
 389     /// `String`s have an internal buffer to hold their data. The capacity is
 390     /// the length of that buffer, and can be queried with the [`capacity`]
 391     /// method. This method creates an empty `String`, but one with an initial
 392     /// buffer that can hold `capacity` bytes. This is useful when you may be
 393     /// appending a bunch of data to the `String`, reducing the number of
 394     /// reallocations it needs to do.
 395     ///
 396     /// [`capacity`]: #method.capacity
 397     ///
 398     /// If the given capacity is `0`, no allocation will occur, and this method
 399     /// is identical to the [`new`] method.
 400     ///
 401     /// [`new`]: #method.new
 402     ///
 403     /// # Examples
 404     ///
 405     /// Basic usage:
 406     ///
 407     /// ```
 408     /// let mut s = String::with_capacity(10);
 409     ///
 410     /// // The String contains no chars, even though it has capacity for more
 411     /// assert_eq!(s.len(), 0);
 412     ///
 413     /// // These are all done without reallocating...
 414     /// let cap = s.capacity();
 415     /// for i in 0..10 {
 416     ///     s.push('a');
 417     /// }
 418     ///
 419     /// assert_eq!(s.capacity(), cap);
 420     ///
 421     /// // ...but this may make the vector reallocate
 422     /// s.push('a');
 423     /// ```
 424     #[inline]
 425     #[stable(feature = "rust1", since = "1.0.0")]
 426     pub fn with_capacity(capacity: usize) -> String {
 427         String { vec: Vec::with_capacity(capacity) }
 428     }
 429
 430     // HACK(japaric): with cfg(test) the inherent `[T]::to_vec` method, which is
 431     // required for this method definition, is not available. Since we don't
 432     // require this method for testing purposes, I'll just stub it
 433     // NB see the slice::hack module in slice.rs for more information
 434     #[inline]
 435     #[cfg(test)]
 436     pub fn from_str(_: &str) -> String {
 437         panic!("not available with cfg(test)");
 438     }
 439
 440     /// Converts a vector of bytes to a `String`.
 441     ///
 442     /// A string slice ([`&str`]) is made of bytes ([`u8`]), and a vector of bytes
 443     /// ([`Vec<u8>`]) is made of bytes, so this function converts between the
 444     /// two. Not all byte slices are valid `String`s, however: `String`
 445     /// requires that it is valid UTF-8. `from_utf8()` checks to ensure that
 446     /// the bytes are valid UTF-8, and then does the conversion.
 447     ///
 448     /// If you are sure that the byte slice is valid UTF-8, and you don't want
 449     /// to incur the overhead of the validity check, there is an unsafe version
 450     /// of this function, [`from_utf8_unchecked`], which has the same behavior
 451     /// but skips the check.
 452     ///
 453     /// This method will take care to not copy the vector, for efficiency's
 454     /// sake.
 455     ///
 456     /// If you need a [`&str`] instead of a `String`, consider
 457     /// [`str::from_utf8`].
 458     ///
 459     /// The inverse of this method is [`as_bytes`].
 460     ///
 461     /// # Errors
 462     ///
 463     /// Returns [`Err`] if the slice is not UTF-8 with a description as to why the
 464     /// provided bytes are not UTF-8. The vector you moved in is also included.
 465     ///
 466     /// # Examples
 467     ///
 468     /// Basic usage:
 469     ///
 470     /// ```
 471     /// // some bytes, in a vector
 472     /// let sparkle_heart = vec![240, 159, 146, 150];
 473     ///
 474     /// // We know these bytes are valid, so we'll use `unwrap()`.
 475     /// let sparkle_heart = String::from_utf8(sparkle_heart).unwrap();
 476     ///
 477     /// assert_eq!("💖", sparkle_heart);
 478     /// ```
 479     ///
 480     /// Incorrect bytes:
 481     ///
 482     /// ```
 483     /// // some invalid bytes, in a vector
 484     /// let sparkle_heart = vec![0, 159, 146, 150];
 485     ///
 486     /// assert!(String::from_utf8(sparkle_heart).is_err());
 487     /// ```
 488     ///
 489     /// See the docs for [`FromUtf8Error`] for more details on what you can do
 490     /// with this error.
 491     ///
 492     /// [`from_utf8_unchecked`]: struct.String.html#method.from_utf8_unchecked
 493     /// [`&str`]: ../../std/primitive.str.html
 494     /// [`u8`]: ../../std/primitive.u8.html
 495     /// [`Vec<u8>`]: ../../std/vec/struct.Vec.html
 496     /// [`str::from_utf8`]: ../../std/str/fn.from_utf8.html
 497     /// [`as_bytes`]: struct.String.html#method.as_bytes
 498     /// [`FromUtf8Error`]: struct.FromUtf8Error.html
 499     /// [`Err`]: ../../stdresult/enum.Result.html#variant.Err
 500     #[inline]
 501     #[stable(feature = "rust1", since = "1.0.0")]
 502     pub fn from_utf8(vec: Vec<u8>) -> Result<String, FromUtf8Error> {
 503         match str::from_utf8(&vec) {
 504             Ok(..) => Ok(String { vec: vec }),
 505             Err(e) => {
 506                 Err(FromUtf8Error {
 507                     bytes: vec,
 508                     error: e,
 509                 })
 510             }
 511         }
 512     }
 513
 514     /// Converts a slice of bytes to a string, including invalid characters.
 515     ///
 516     /// Strings are made of bytes ([`u8`]), and a slice of bytes
 517     /// ([`&[u8]`][byteslice]) is made of bytes, so this function converts
 518     /// between the two. Not all byte slices are valid strings, however: strings
 519     /// are required to be valid UTF-8. During this conversion,
 520     /// `from_utf8_lossy()` will replace any invalid UTF-8 sequences with
 521     /// `U+FFFD REPLACEMENT CHARACTER`, which looks like this: �
 522     ///
 523     /// [`u8`]: ../../std/primitive.u8.html
 524     /// [byteslice]: ../../std/primitive.slice.html
 525     ///
 526     /// If you are sure that the byte slice is valid UTF-8, and you don't want
 527     /// to incur the overhead of the conversion, there is an unsafe version
 528     /// of this function, [`from_utf8_unchecked`], which has the same behavior
 529     /// but skips the checks.
 530     ///
 531     /// [`from_utf8_unchecked`]: struct.String.html#method.from_utf8_unchecked
 532     ///
 533     /// This function returns a [`Cow<'a, str>`]. If our byte slice is invalid
 534     /// UTF-8, then we need to insert the replacement characters, which will
 535     /// change the size of the string, and hence, require a `String`. But if
 536     /// it's already valid UTF-8, we don't need a new allocation. This return
 537     /// type allows us to handle both cases.
 538     ///
 539     /// [`Cow<'a, str>`]: ../../std/borrow/enum.Cow.html
 540     ///
 541     /// # Examples
 542     ///
 543     /// Basic usage:
 544     ///
 545     /// ```
 546     /// // some bytes, in a vector
 547     /// let sparkle_heart = vec![240, 159, 146, 150];
 548     ///
 549     /// let sparkle_heart = String::from_utf8_lossy(&sparkle_heart);
 550     ///
 551     /// assert_eq!("💖", sparkle_heart);
 552     /// ```
 553     ///
 554     /// Incorrect bytes:
 555     ///
 556     /// ```
 557     /// // some invalid bytes
 558     /// let input = b"Hello \xF0\x90\x80World";
 559     /// let output = String::from_utf8_lossy(input);
 560     ///
 561     /// assert_eq!("Hello �World", output);
 562     /// ```
 563     #[stable(feature = "rust1", since = "1.0.0")]
 564     pub fn from_utf8_lossy<'a>(v: &'a [u8]) -> Cow<'a, str> {
 565         let mut iter = lossy::Utf8Lossy::from_bytes(v).chunks();
 566
 567         let (first_valid, first_broken) = if let Some(chunk) = iter.next() {
 568             let lossy::Utf8LossyChunk { valid, broken } = chunk;
 569             if valid.len() == v.len() {
 570                 debug_assert!(broken.is_empty());
 571                 return Cow::Borrowed(valid);
 572             }
 573             (valid, broken)
 574         } else {
 575             return Cow::Borrowed("");
 576         };
 577
 578         const REPLACEMENT: &'static str = "\u{FFFD}";
 579
 580         let mut res = String::with_capacity(v.len());
 581         res.push_str(first_valid);
 582         if !first_broken.is_empty() {
 583             res.push_str(REPLACEMENT);
 584         }
 585
 586         for lossy::Utf8LossyChunk { valid, broken } in iter {
 587             res.push_str(valid);
 588             if !broken.is_empty() {
 589                 res.push_str(REPLACEMENT);
 590             }
 591         }
 592
 593         Cow::Owned(res)
 594     }
 595
 596     /// Decode a UTF-16 encoded vector `v` into a `String`, returning [`Err`]
 597     /// if `v` contains any invalid data.
 598     ///
 599     /// [`Err`]: ../../std/result/enum.Result.html#variant.Err
 600     ///
 601     /// # Examples
 602     ///
 603     /// Basic usage:
 604     ///
 605     /// ```
 606     /// // 𝄞music
 607     /// let v = &[0xD834, 0xDD1E, 0x006d, 0x0075,
 608     ///           0x0073, 0x0069, 0x0063];
 609     /// assert_eq!(String::from("𝄞music"),
 610     ///            String::from_utf16(v).unwrap());
 611     ///
 612     /// // 𝄞mu<invalid>ic
 613     /// let v = &[0xD834, 0xDD1E, 0x006d, 0x0075,
 614     ///           0xD800, 0x0069, 0x0063];
 615     /// assert!(String::from_utf16(v).is_err());
 616     /// ```
 617     #[stable(feature = "rust1", since = "1.0.0")]
 618     pub fn from_utf16(v: &[u16]) -> Result<String, FromUtf16Error> {
 619         decode_utf16(v.iter().cloned()).collect::<Result<_, _>>().map_err(|_| FromUtf16Error(()))
 620     }
 621
 622     /// Decode a UTF-16 encoded slice `v` into a `String`, replacing
 623     /// invalid data with the replacement character (U+FFFD).
 624     ///
 625     /// Unlike [`from_utf8_lossy`] which returns a [`Cow<'a, str>`],
 626     /// `from_utf16_lossy` returns a `String` since the UTF-16 to UTF-8
 627     /// conversion requires a memory allocation.
 628     ///
 629     /// [`from_utf8_lossy`]: #method.from_utf8_lossy
 630     /// [`Cow<'a, str>`]: ../borrow/enum.Cow.html
 631     ///
 632     /// # Examples
 633     ///
 634     /// Basic usage:
 635     ///
 636     /// ```
 637     /// // 𝄞mus<invalid>ic<invalid>
 638     /// let v = &[0xD834, 0xDD1E, 0x006d, 0x0075,
 639     ///           0x0073, 0xDD1E, 0x0069, 0x0063,
 640     ///           0xD834];
 641     ///
 642     /// assert_eq!(String::from("𝄞mus\u{FFFD}ic\u{FFFD}"),
 643     ///            String::from_utf16_lossy(v));
 644     /// ```
 645     #[inline]
 646     #[stable(feature = "rust1", since = "1.0.0")]
 647     pub fn from_utf16_lossy(v: &[u16]) -> String {
 648         decode_utf16(v.iter().cloned()).map(|r| r.unwrap_or(REPLACEMENT_CHARACTER)).collect()
 649     }
 650
 651     /// Creates a new `String` from a length, capacity, and pointer.
 652     ///
 653     /// # Safety
 654     ///
 655     /// This is highly unsafe, due to the number of invariants that aren't
 656     /// checked:
 657     ///
 658     /// * The memory at `ptr` needs to have been previously allocated by the
 659     ///   same allocator the standard library uses.
 660     /// * `length` needs to be less than or equal to `capacity`.
 661     /// * `capacity` needs to be the correct value.
 662     ///
 663     /// Violating these may cause problems like corrupting the allocator's
 664     /// internal data structures.
 665     ///
 666     /// The ownership of `ptr` is effectively transferred to the
 667     /// `String` which may then deallocate, reallocate or change the
 668     /// contents of memory pointed to by the pointer at will. Ensure
 669     /// that nothing else uses the pointer after calling this
 670     /// function.
 671     ///
 672     /// # Examples
 673     ///
 674     /// Basic usage:
 675     ///
 676     /// ```
 677     /// use std::mem;
 678     ///
 679     /// unsafe {
 680     ///     let s = String::from("hello");
 681     ///     let ptr = s.as_ptr();
 682     ///     let len = s.len();
 683     ///     let capacity = s.capacity();
 684     ///
 685     ///     mem::forget(s);
 686     ///
 687     ///     let s = String::from_raw_parts(ptr as *mut _, len, capacity);
 688     ///
 689     ///     assert_eq!(String::from("hello"), s);
 690     /// }
 691     /// ```
 692     #[inline]
 693     #[stable(feature = "rust1", since = "1.0.0")]
 694     pub unsafe fn from_raw_parts(buf: *mut u8, length: usize, capacity: usize) -> String {
 695         String { vec: Vec::from_raw_parts(buf, length, capacity) }
 696     }
 697
 698     /// Converts a vector of bytes to a `String` without checking that the
 699     /// string contains valid UTF-8.
 700     ///
 701     /// See the safe version, [`from_utf8`], for more details.
 702     ///
 703     /// [`from_utf8`]: struct.String.html#method.from_utf8
 704     ///
 705     /// # Safety
 706     ///
 707     /// This function is unsafe because it does not check that the bytes passed
 708     /// to it are valid UTF-8. If this constraint is violated, it may cause
 709     /// memory unsafety issues with future users of the `String`, as the rest of
 710     /// the standard library assumes that `String`s are valid UTF-8.
 711     ///
 712     /// # Examples
 713     ///
 714     /// Basic usage:
 715     ///
 716     /// ```
 717     /// // some bytes, in a vector
 718     /// let sparkle_heart = vec![240, 159, 146, 150];
 719     ///
 720     /// let sparkle_heart = unsafe {
 721     ///     String::from_utf8_unchecked(sparkle_heart)
 722     /// };
 723     ///
 724     /// assert_eq!("💖", sparkle_heart);
 725     /// ```
 726     #[inline]
 727     #[stable(feature = "rust1", since = "1.0.0")]
 728     pub unsafe fn from_utf8_unchecked(bytes: Vec<u8>) -> String {
 729         String { vec: bytes }
 730     }
 731
 732     /// Converts a `String` into a byte vector.
 733     ///
 734     /// This consumes the `String`, so we do not need to copy its contents.
 735     ///
 736     /// # Examples
 737     ///
 738     /// Basic usage:
 739     ///
 740     /// ```
 741     /// let s = String::from("hello");
 742     /// let bytes = s.into_bytes();
 743     ///
 744     /// assert_eq!(&[104, 101, 108, 108, 111][..], &bytes[..]);
 745     /// ```
 746     #[inline]
 747     #[stable(feature = "rust1", since = "1.0.0")]
 748     pub fn into_bytes(self) -> Vec<u8> {
 749         self.vec
 750     }
 751
 752     /// Extracts a string slice containing the entire string.
 753     ///
 754     /// # Examples
 755     ///
 756     /// Basic usage:
 757     ///
 758     /// ```
 759     /// let s = String::from("foo");
 760     ///
 761     /// assert_eq!("foo", s.as_str());
 762     /// ```
 763     #[inline]
 764     #[stable(feature = "string_as_str", since = "1.7.0")]
 765     pub fn as_str(&self) -> &str {
 766         self
 767     }
 768
 769     /// Converts a `String` into a mutable string slice.
 770     ///
 771     /// # Examples
 772     ///
 773     /// Basic usage:
 774     ///
 775     /// ```
 776     /// let mut s = String::from("foobar");
 777     /// let s_mut_str = s.as_mut_str();
 778     ///
 779     /// s_mut_str.make_ascii_uppercase();
 780     ///
 781     /// assert_eq!("FOOBAR", s_mut_str);
 782     /// ```
 783     #[inline]
 784     #[stable(feature = "string_as_str", since = "1.7.0")]
 785     pub fn as_mut_str(&mut self) -> &mut str {
 786         self
 787     }
 788
 789     /// Appends a given string slice onto the end of this `String`.
 790     ///
 791     /// # Examples
 792     ///
 793     /// Basic usage:
 794     ///
 795     /// ```
 796     /// let mut s = String::from("foo");
 797     ///
 798     /// s.push_str("bar");
 799     ///
 800     /// assert_eq!("foobar", s);
 801     /// ```
 802     #[inline]
 803     #[stable(feature = "rust1", since = "1.0.0")]
 804     pub fn push_str(&mut self, string: &str) {
 805         self.vec.extend_from_slice(string.as_bytes())
 806     }
 807
 808     /// Returns this `String`'s capacity, in bytes.
 809     ///
 810     /// # Examples
 811     ///
 812     /// Basic usage:
 813     ///
 814     /// ```
 815     /// let s = String::with_capacity(10);
 816     ///
 817     /// assert!(s.capacity() >= 10);
 818     /// ```
 819     #[inline]
 820     #[stable(feature = "rust1", since = "1.0.0")]
 821     pub fn capacity(&self) -> usize {
 822         self.vec.capacity()
 823     }
 824
 825     /// Ensures that this `String`'s capacity is at least `additional` bytes
 826     /// larger than its length.
 827     ///
 828     /// The capacity may be increased by more than `additional` bytes if it
 829     /// chooses, to prevent frequent reallocations.
 830     ///
 831     /// If you do not want this "at least" behavior, see the [`reserve_exact`]
 832     /// method.
 833     ///
 834     /// # Panics
 835     ///
 836     /// Panics if the new capacity overflows [`usize`].
 837     ///
 838     /// [`reserve_exact`]: struct.String.html#method.reserve_exact
 839     /// [`usize`]: ../../std/primitive.usize.html
 840     ///
 841     /// # Examples
 842     ///
 843     /// Basic usage:
 844     ///
 845     /// ```
 846     /// let mut s = String::new();
 847     ///
 848     /// s.reserve(10);
 849     ///
 850     /// assert!(s.capacity() >= 10);
 851     /// ```
 852     ///
 853     /// This may not actually increase the capacity:
 854     ///
 855     /// ```
 856     /// let mut s = String::with_capacity(10);
 857     /// s.push('a');
 858     /// s.push('b');
 859     ///
 860     /// // s now has a length of 2 and a capacity of 10
 861     /// assert_eq!(2, s.len());
 862     /// assert_eq!(10, s.capacity());
 863     ///
 864     /// // Since we already have an extra 8 capacity, calling this...
 865     /// s.reserve(8);
 866     ///
 867     /// // ... doesn't actually increase.
 868     /// assert_eq!(10, s.capacity());
 869     /// ```
 870     #[inline]
 871     #[stable(feature = "rust1", since = "1.0.0")]
 872     pub fn reserve(&mut self, additional: usize) {
 873         self.vec.reserve(additional)
 874     }
 875
 876     /// Ensures that this `String`'s capacity is `additional` bytes
 877     /// larger than its length.
 878     ///
 879     /// Consider using the [`reserve`] method unless you absolutely know
 880     /// better than the allocator.
 881     ///
 882     /// [`reserve`]: #method.reserve
 883     ///
 884     /// # Panics
 885     ///
 886     /// Panics if the new capacity overflows `usize`.
 887     ///
 888     /// # Examples
 889     ///
 890     /// Basic usage:
 891     ///
 892     /// ```
 893     /// let mut s = String::new();
 894     ///
 895     /// s.reserve_exact(10);
 896     ///
 897     /// assert!(s.capacity() >= 10);
 898     /// ```
 899     ///
 900     /// This may not actually increase the capacity:
 901     ///
 902     /// ```
 903     /// let mut s = String::with_capacity(10);
 904     /// s.push('a');
 905     /// s.push('b');
 906     ///
 907     /// // s now has a length of 2 and a capacity of 10
 908     /// assert_eq!(2, s.len());
 909     /// assert_eq!(10, s.capacity());
 910     ///
 911     /// // Since we already have an extra 8 capacity, calling this...
 912     /// s.reserve_exact(8);
 913     ///
 914     /// // ... doesn't actually increase.
 915     /// assert_eq!(10, s.capacity());
 916     /// ```
 917     #[inline]
 918     #[stable(feature = "rust1", since = "1.0.0")]
 919     pub fn reserve_exact(&mut self, additional: usize) {
 920         self.vec.reserve_exact(additional)
 921     }
 922
 923     /// Shrinks the capacity of this `String` to match its length.
 924     ///
 925     /// # Examples
 926     ///
 927     /// Basic usage:
 928     ///
 929     /// ```
 930     /// let mut s = String::from("foo");
 931     ///
 932     /// s.reserve(100);
 933     /// assert!(s.capacity() >= 100);
 934     ///
 935     /// s.shrink_to_fit();
 936     /// assert_eq!(3, s.capacity());
 937     /// ```
 938     #[inline]
 939     #[stable(feature = "rust1", since = "1.0.0")]
 940     pub fn shrink_to_fit(&mut self) {
 941         self.vec.shrink_to_fit()
 942     }
 943
 944     /// Appends the given [`char`] to the end of this `String`.
 945     ///
 946     /// [`char`]: ../../std/primitive.char.html
 947     ///
 948     /// # Examples
 949     ///
 950     /// Basic usage:
 951     ///
 952     /// ```
 953     /// let mut s = String::from("abc");
 954     ///
 955     /// s.push('1');
 956     /// s.push('2');
 957     /// s.push('3');
 958     ///
 959     /// assert_eq!("abc123", s);
 960     /// ```
 961     #[inline]
 962     #[stable(feature = "rust1", since = "1.0.0")]
 963     pub fn push(&mut self, ch: char) {
 964         match ch.len_utf8() {
 965             1 => self.vec.push(ch as u8),
 966             _ => self.vec.extend_from_slice(ch.encode_utf8(&mut [0; 4]).as_bytes()),
 967         }
 968     }
 969
 970     /// Returns a byte slice of this `String`'s contents.
 971     ///
 972     /// The inverse of this method is [`from_utf8`].
 973     ///
 974     /// [`from_utf8`]: #method.from_utf8
 975     ///
 976     /// # Examples
 977     ///
 978     /// Basic usage:
 979     ///
 980     /// ```
 981     /// let s = String::from("hello");
 982     ///
 983     /// assert_eq!(&[104, 101, 108, 108, 111], s.as_bytes());
 984     /// ```
 985     #[inline]
 986     #[stable(feature = "rust1", since = "1.0.0")]
 987     pub fn as_bytes(&self) -> &[u8] {
 988         &self.vec
 989     }
 990
 991     /// Shortens this `String` to the specified length.
 992     ///
 993     /// If `new_len` is greater than the string's current length, this has no
 994     /// effect.
 995     ///
 996     /// Note that this method has no effect on the allocated capacity
 997     /// of the string
 998     ///
 999     /// # Panics
1000     ///
1001     /// Panics if `new_len` does not lie on a [`char`] boundary.
1002     ///
1003     /// [`char`]: ../../std/primitive.char.html
1004     ///
1005     /// # Examples
1006     ///
1007     /// Basic usage:
1008     ///
1009     /// ```
1010     /// let mut s = String::from("hello");
1011     ///
1012     /// s.truncate(2);
1013     ///
1014     /// assert_eq!("he", s);
1015     /// ```
1016     #[inline]
1017     #[stable(feature = "rust1", since = "1.0.0")]
1018     pub fn truncate(&mut self, new_len: usize) {
1019         if new_len <= self.len() {
1020             assert!(self.is_char_boundary(new_len));
1021             self.vec.truncate(new_len)
1022         }
1023     }
1024
1025     /// Removes the last character from the string buffer and returns it.
1026     ///
1027     /// Returns [`None`] if this `String` is empty.
1028     ///
1029     /// [`None`]: ../../std/option/enum.Option.html#variant.None
1030     ///
1031     /// # Examples
1032     ///
1033     /// Basic usage:
1034     ///
1035     /// ```
1036     /// let mut s = String::from("foo");
1037     ///
1038     /// assert_eq!(s.pop(), Some('o'));
1039     /// assert_eq!(s.pop(), Some('o'));
1040     /// assert_eq!(s.pop(), Some('f'));
1041     ///
1042     /// assert_eq!(s.pop(), None);
1043     /// ```
1044     #[inline]
1045     #[stable(feature = "rust1", since = "1.0.0")]
1046     pub fn pop(&mut self) -> Option<char> {
1047         let ch = self.chars().rev().next()?;
1048         let newlen = self.len() - ch.len_utf8();
1049         unsafe {
1050             self.vec.set_len(newlen);
1051         }
1052         Some(ch)
1053     }
1054
1055     /// Removes a [`char`] from this `String` at a byte position and returns it.
1056     ///
1057     /// This is an `O(n)` operation, as it requires copying every element in the
1058     /// buffer.
1059     ///
1060     /// # Panics
1061     ///
1062     /// Panics if `idx` is larger than or equal to the `String`'s length,
1063     /// or if it does not lie on a [`char`] boundary.
1064     ///
1065     /// [`char`]: ../../std/primitive.char.html
1066     ///
1067     /// # Examples
1068     ///
1069     /// Basic usage:
1070     ///
1071     /// ```
1072     /// let mut s = String::from("foo");
1073     ///
1074     /// assert_eq!(s.remove(0), 'f');
1075     /// assert_eq!(s.remove(1), 'o');
1076     /// assert_eq!(s.remove(0), 'o');
1077     /// ```
1078     #[inline]
1079     #[stable(feature = "rust1", since = "1.0.0")]
1080     pub fn remove(&mut self, idx: usize) -> char {
1081         let ch = match self[idx..].chars().next() {
1082             Some(ch) => ch,
1083             None => panic!("cannot remove a char from the end of a string"),
1084         };
1085
1086         let next = idx + ch.len_utf8();
1087         let len = self.len();
1088         unsafe {
1089             ptr::copy(self.vec.as_ptr().offset(next as isize),
1090                       self.vec.as_mut_ptr().offset(idx as isize),
1091                       len - next);
1092             self.vec.set_len(len - (next - idx));
1093         }
1094         ch
1095     }
1096
1097     /// Retains only the characters specified by the predicate.
1098     ///
1099     /// In other words, remove all characters `c` such that `f(c)` returns `false`.
1100     /// This method operates in place and preserves the order of the retained
1101     /// characters.
1102     ///
1103     /// # Examples
1104     ///
1105     /// ```
1106     /// #![feature(string_retain)]
1107     ///
1108     /// let mut s = String::from("f_o_ob_ar");
1109     ///
1110     /// s.retain(|c| c != '_');
1111     ///
1112     /// assert_eq!(s, "foobar");
1113     /// ```
1114     #[inline]
1115     #[unstable(feature = "string_retain", issue = "43874")]
1116     pub fn retain<F>(&mut self, mut f: F)
1117         where F: FnMut(char) -> bool
1118     {
1119         let len = self.len();
1120         let mut del_bytes = 0;
1121         let mut idx = 0;
1122
1123         while idx < len {
1124             let ch = unsafe {
1125                 self.slice_unchecked(idx, len).chars().next().unwrap()
1126             };
1127             let ch_len = ch.len_utf8();
1128
1129             if !f(ch) {
1130                 del_bytes += ch_len;
1131             } else if del_bytes > 0 {
1132                 unsafe {
1133                     ptr::copy(self.vec.as_ptr().offset(idx as isize),
1134                               self.vec.as_mut_ptr().offset((idx - del_bytes) as isize),
1135                               ch_len);
1136                 }
1137             }
1138
1139             // Point idx to the next char
1140             idx += ch_len;
1141         }
1142
1143         if del_bytes > 0 {
1144             unsafe { self.vec.set_len(len - del_bytes); }
1145         }
1146     }
1147
1148     /// Inserts a character into this `String` at a byte position.
1149     ///
1150     /// This is an `O(n)` operation as it requires copying every element in the
1151     /// buffer.
1152     ///
1153     /// # Panics
1154     ///
1155     /// Panics if `idx` is larger than the `String`'s length, or if it does not
1156     /// lie on a [`char`] boundary.
1157     ///
1158     /// [`char`]: ../../std/primitive.char.html
1159     ///
1160     /// # Examples
1161     ///
1162     /// Basic usage:
1163     ///
1164     /// ```
1165     /// let mut s = String::with_capacity(3);
1166     ///
1167     /// s.insert(0, 'f');
1168     /// s.insert(1, 'o');
1169     /// s.insert(2, 'o');
1170     ///
1171     /// assert_eq!("foo", s);
1172     /// ```
1173     #[inline]
1174     #[stable(feature = "rust1", since = "1.0.0")]
1175     pub fn insert(&mut self, idx: usize, ch: char) {
1176         assert!(self.is_char_boundary(idx));
1177         let mut bits = [0; 4];
1178         let bits = ch.encode_utf8(&mut bits).as_bytes();
1179
1180         unsafe {
1181             self.insert_bytes(idx, bits);
1182         }
1183     }
1184
1185     unsafe fn insert_bytes(&mut self, idx: usize, bytes: &[u8]) {
1186         let len = self.len();
1187         let amt = bytes.len();
1188         self.vec.reserve(amt);
1189
1190         ptr::copy(self.vec.as_ptr().offset(idx as isize),
1191                   self.vec.as_mut_ptr().offset((idx + amt) as isize),
1192                   len - idx);
1193         ptr::copy(bytes.as_ptr(),
1194                   self.vec.as_mut_ptr().offset(idx as isize),
1195                   amt);
1196         self.vec.set_len(len + amt);
1197     }
1198
1199     /// Inserts a string slice into this `String` at a byte position.
1200     ///
1201     /// This is an `O(n)` operation as it requires copying every element in the
1202     /// buffer.
1203     ///
1204     /// # Panics
1205     ///
1206     /// Panics if `idx` is larger than the `String`'s length, or if it does not
1207     /// lie on a [`char`] boundary.
1208     ///
1209     /// [`char`]: ../../std/primitive.char.html
1210     ///
1211     /// # Examples
1212     ///
1213     /// Basic usage:
1214     ///
1215     /// ```
1216     /// let mut s = String::from("bar");
1217     ///
1218     /// s.insert_str(0, "foo");
1219     ///
1220     /// assert_eq!("foobar", s);
1221     /// ```
1222     #[inline]
1223     #[stable(feature = "insert_str", since = "1.16.0")]
1224     pub fn insert_str(&mut self, idx: usize, string: &str) {
1225         assert!(self.is_char_boundary(idx));
1226
1227         unsafe {
1228             self.insert_bytes(idx, string.as_bytes());
1229         }
1230     }
1231
1232     /// Returns a mutable reference to the contents of this `String`.
1233     ///
1234     /// # Safety
1235     ///
1236     /// This function is unsafe because it does not check that the bytes passed
1237     /// to it are valid UTF-8. If this constraint is violated, it may cause
1238     /// memory unsafety issues with future users of the `String`, as the rest of
1239     /// the standard library assumes that `String`s are valid UTF-8.
1240     ///
1241     /// # Examples
1242     ///
1243     /// Basic usage:
1244     ///
1245     /// ```
1246     /// let mut s = String::from("hello");
1247     ///
1248     /// unsafe {
1249     ///     let vec = s.as_mut_vec();
1250     ///     assert_eq!(&[104, 101, 108, 108, 111][..], &vec[..]);
1251     ///
1252     ///     vec.reverse();
1253     /// }
1254     /// assert_eq!(s, "olleh");
1255     /// ```
1256     #[inline]
1257     #[stable(feature = "rust1", since = "1.0.0")]
1258     pub unsafe fn as_mut_vec(&mut self) -> &mut Vec<u8> {
1259         &mut self.vec
1260     }
1261
1262     /// Returns the length of this `String`, in bytes.
1263     ///
1264     /// # Examples
1265     ///
1266     /// Basic usage:
1267     ///
1268     /// ```
1269     /// let a = String::from("foo");
1270     ///
1271     /// assert_eq!(a.len(), 3);
1272     /// ```
1273     #[inline]
1274     #[stable(feature = "rust1", since = "1.0.0")]
1275     pub fn len(&self) -> usize {
1276         self.vec.len()
1277     }
1278
1279     /// Returns `true` if this `String` has a length of zero.
1280     ///
1281     /// Returns `false` otherwise.
1282     ///
1283     /// # Examples
1284     ///
1285     /// Basic usage:
1286     ///
1287     /// ```
1288     /// let mut v = String::new();
1289     /// assert!(v.is_empty());
1290     ///
1291     /// v.push('a');
1292     /// assert!(!v.is_empty());
1293     /// ```
1294     #[inline]
1295     #[stable(feature = "rust1", since = "1.0.0")]
1296     pub fn is_empty(&self) -> bool {
1297         self.len() == 0
1298     }
1299
1300     /// Splits the string into two at the given index.
1301     ///
1302     /// Returns a newly allocated `String`. `self` contains bytes `[0, at)`, and
1303     /// the returned `String` contains bytes `[at, len)`. `at` must be on the
1304     /// boundary of a UTF-8 code point.
1305     ///
1306     /// Note that the capacity of `self` does not change.
1307     ///
1308     /// # Panics
1309     ///
1310     /// Panics if `at` is not on a `UTF-8` code point boundary, or if it is beyond the last
1311     /// code point of the string.
1312     ///
1313     /// # Examples
1314     ///
1315     /// ```
1316     /// # fn main() {
1317     /// let mut hello = String::from("Hello, World!");
1318     /// let world = hello.split_off(7);
1319     /// assert_eq!(hello, "Hello, ");
1320     /// assert_eq!(world, "World!");
1321     /// # }
1322     /// ```
1323     #[inline]
1324     #[stable(feature = "string_split_off", since = "1.16.0")]
1325     pub fn split_off(&mut self, at: usize) -> String {
1326         assert!(self.is_char_boundary(at));
1327         let other = self.vec.split_off(at);
1328         unsafe { String::from_utf8_unchecked(other) }
1329     }
1330
1331     /// Truncates this `String`, removing all contents.
1332     ///
1333     /// While this means the `String` will have a length of zero, it does not
1334     /// touch its capacity.
1335     ///
1336     /// # Examples
1337     ///
1338     /// Basic usage:
1339     ///
1340     /// ```
1341     /// let mut s = String::from("foo");
1342     ///
1343     /// s.clear();
1344     ///
1345     /// assert!(s.is_empty());
1346     /// assert_eq!(0, s.len());
1347     /// assert_eq!(3, s.capacity());
1348     /// ```
1349     #[inline]
1350     #[stable(feature = "rust1", since = "1.0.0")]
1351     pub fn clear(&mut self) {
1352         self.vec.clear()
1353     }
1354
1355     /// Creates a draining iterator that removes the specified range in the string
1356     /// and yields the removed chars.
1357     ///
1358     /// Note: The element range is removed even if the iterator is not
1359     /// consumed until the end.
1360     ///
1361     /// # Panics
1362     ///
1363     /// Panics if the starting point or end point do not lie on a [`char`]
1364     /// boundary, or if they're out of bounds.
1365     ///
1366     /// [`char`]: ../../std/primitive.char.html
1367     ///
1368     /// # Examples
1369     ///
1370     /// Basic usage:
1371     ///
1372     /// ```
1373     /// let mut s = String::from("α is alpha, β is beta");
1374     /// let beta_offset = s.find('β').unwrap_or(s.len());
1375     ///
1376     /// // Remove the range up until the β from the string
1377     /// let t: String = s.drain(..beta_offset).collect();
1378     /// assert_eq!(t, "α is alpha, ");
1379     /// assert_eq!(s, "β is beta");
1380     ///
1381     /// // A full range clears the string
1382     /// s.drain(..);
1383     /// assert_eq!(s, "");
1384     /// ```
1385     #[stable(feature = "drain", since = "1.6.0")]
1386     pub fn drain<R>(&mut self, range: R) -> Drain
1387         where R: RangeArgument<usize>
1388     {
1389         // Memory safety
1390         //
1391         // The String version of Drain does not have the memory safety issues
1392         // of the vector version. The data is just plain bytes.
1393         // Because the range removal happens in Drop, if the Drain iterator is leaked,
1394         // the removal will not happen.
1395         let len = self.len();
1396         let start = match range.start() {
1397             Included(&n) => n,
1398             Excluded(&n) => n + 1,
1399             Unbounded => 0,
1400         };
1401         let end = match range.end() {
1402             Included(&n) => n + 1,
1403             Excluded(&n) => n,
1404             Unbounded => len,
1405         };
1406
1407         // Take out two simultaneous borrows. The &mut String won't be accessed
1408         // until iteration is over, in Drop.
1409         let self_ptr = self as *mut _;
1410         // slicing does the appropriate bounds checks
1411         let chars_iter = self[start..end].chars();
1412
1413         Drain {
1414             start,
1415             end,
1416             iter: chars_iter,
1417             string: self_ptr,
1418         }
1419     }
1420
1421     /// Creates a splicing iterator that removes the specified range in the string,
1422     /// and replaces it with the given string.
1423     /// The given string doesn't need to be the same length as the range.
1424     ///
1425     /// Note: Unlike [`Vec::splice`], the replacement happens eagerly, and this
1426     /// method does not return the removed chars.
1427     ///
1428     /// # Panics
1429     ///
1430     /// Panics if the starting point or end point do not lie on a [`char`]
1431     /// boundary, or if they're out of bounds.
1432     ///
1433     /// [`char`]: ../../std/primitive.char.html
1434     /// [`Vec::splice`]: ../../std/vec/struct.Vec.html#method.splice
1435     ///
1436     /// # Examples
1437     ///
1438     /// Basic usage:
1439     ///
1440     /// ```
1441     /// #![feature(splice)]
1442     /// let mut s = String::from("α is alpha, β is beta");
1443     /// let beta_offset = s.find('β').unwrap_or(s.len());
1444     ///
1445     /// // Replace the range up until the β from the string
1446     /// s.splice(..beta_offset, "Α is capital alpha; ");
1447     /// assert_eq!(s, "Α is capital alpha; β is beta");
1448     /// ```
1449     #[unstable(feature = "splice", reason = "recently added", issue = "44643")]
1450     pub fn splice<R>(&mut self, range: R, replace_with: &str)
1451         where R: RangeArgument<usize>
1452     {
1453         // Memory safety
1454         //
1455         // The String version of Splice does not have the memory safety issues
1456         // of the vector version. The data is just plain bytes.
1457
1458         match range.start() {
1459              Included(&n) => assert!(self.is_char_boundary(n)),
1460              Excluded(&n) => assert!(self.is_char_boundary(n + 1)),
1461              Unbounded => {},
1462         };
1463         match range.end() {
1464              Included(&n) => assert!(self.is_char_boundary(n + 1)),
1465              Excluded(&n) => assert!(self.is_char_boundary(n)),
1466              Unbounded => {},
1467         };
1468
1469         unsafe {
1470             self.as_mut_vec()
1471         }.splice(range, replace_with.bytes());
1472     }
1473
1474     /// Converts this `String` into a [`Box`]`<`[`str`]`>`.
1475     ///
1476     /// This will drop any excess capacity.
1477     ///
1478     /// [`Box`]: ../../std/boxed/struct.Box.html
1479     /// [`str`]: ../../std/primitive.str.html
1480     ///
1481     /// # Examples
1482     ///
1483     /// Basic usage:
1484     ///
1485     /// ```
1486     /// let s = String::from("hello");
1487     ///
1488     /// let b = s.into_boxed_str();
1489     /// ```
1490     #[stable(feature = "box_str", since = "1.4.0")]
1491     pub fn into_boxed_str(self) -> Box<str> {
1492         let slice = self.vec.into_boxed_slice();
1493         unsafe { from_boxed_utf8_unchecked(slice) }
1494     }
1495 }
1496
1497 impl FromUtf8Error {
1498     /// Returns a slice of [`u8`]s bytes that were attempted to convert to a `String`.
1499     ///
1500     /// # Examples
1501     ///
1502     /// Basic usage:
1503     ///
1504     /// ```
1505     /// #![feature(from_utf8_error_as_bytes)]
1506     /// // some invalid bytes, in a vector
1507     /// let bytes = vec![0, 159];
1508     ///
1509     /// let value = String::from_utf8(bytes);
1510     ///
1511     /// assert_eq!(&[0, 159], value.unwrap_err().as_bytes());
1512     /// ```
1513     #[unstable(feature = "from_utf8_error_as_bytes", reason = "recently added", issue = "40895")]
1514     pub fn as_bytes(&self) -> &[u8] {
1515         &self.bytes[..]
1516     }
1517
1518     /// Returns the bytes that were attempted to convert to a `String`.
1519     ///
1520     /// This method is carefully constructed to avoid allocation. It will
1521     /// consume the error, moving out the bytes, so that a copy of the bytes
1522     /// does not need to be made.
1523     ///
1524     /// # Examples
1525     ///
1526     /// Basic usage:
1527     ///
1528     /// ```
1529     /// // some invalid bytes, in a vector
1530     /// let bytes = vec![0, 159];
1531     ///
1532     /// let value = String::from_utf8(bytes);
1533     ///
1534     /// assert_eq!(vec![0, 159], value.unwrap_err().into_bytes());
1535     /// ```
1536     #[stable(feature = "rust1", since = "1.0.0")]
1537     pub fn into_bytes(self) -> Vec<u8> {
1538         self.bytes
1539     }
1540
1541     /// Fetch a `Utf8Error` to get more details about the conversion failure.
1542     ///
1543     /// The [`Utf8Error`] type provided by [`std::str`] represents an error that may
1544     /// occur when converting a slice of [`u8`]s to a [`&str`]. In this sense, it's
1545     /// an analogue to `FromUtf8Error`. See its documentation for more details
1546     /// on using it.
1547     ///
1548     /// [`Utf8Error`]: ../../std/str/struct.Utf8Error.html
1549     /// [`std::str`]: ../../std/str/index.html
1550     /// [`u8`]: ../../std/primitive.u8.html
1551     /// [`&str`]: ../../std/primitive.str.html
1552     ///
1553     /// # Examples
1554     ///
1555     /// Basic usage:
1556     ///
1557     /// ```
1558     /// // some invalid bytes, in a vector
1559     /// let bytes = vec![0, 159];
1560     ///
1561     /// let error = String::from_utf8(bytes).unwrap_err().utf8_error();
1562     ///
1563     /// // the first byte is invalid here
1564     /// assert_eq!(1, error.valid_up_to());
1565     /// ```
1566     #[stable(feature = "rust1", since = "1.0.0")]
1567     pub fn utf8_error(&self) -> Utf8Error {
1568         self.error
1569     }
1570 }
1571
1572 #[stable(feature = "rust1", since = "1.0.0")]
1573 impl fmt::Display for FromUtf8Error {
1574     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1575         fmt::Display::fmt(&self.error, f)
1576     }
1577 }
1578
1579 #[stable(feature = "rust1", since = "1.0.0")]
1580 impl fmt::Display for FromUtf16Error {
1581     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1582         fmt::Display::fmt("invalid utf-16: lone surrogate found", f)
1583     }
1584 }
1585
1586 #[stable(feature = "rust1", since = "1.0.0")]
1587 impl Clone for String {
1588     fn clone(&self) -> Self {
1589         String { vec: self.vec.clone() }
1590     }
1591
1592     fn clone_from(&mut self, source: &Self) {
1593         self.vec.clone_from(&source.vec);
1594     }
1595 }
1596
1597 #[stable(feature = "rust1", since = "1.0.0")]
1598 impl FromIterator<char> for String {
1599     fn from_iter<I: IntoIterator<Item = char>>(iter: I) -> String {
1600         let mut buf = String::new();
1601         buf.extend(iter);
1602         buf
1603     }
1604 }
1605
1606 #[stable(feature = "string_from_iter_by_ref", since = "1.17.0")]
1607 impl<'a> FromIterator<&'a char> for String {
1608     fn from_iter<I: IntoIterator<Item = &'a char>>(iter: I) -> String {
1609         let mut buf = String::new();
1610         buf.extend(iter);
1611         buf
1612     }
1613 }
1614
1615 #[stable(feature = "rust1", since = "1.0.0")]
1616 impl<'a> FromIterator<&'a str> for String {
1617     fn from_iter<I: IntoIterator<Item = &'a str>>(iter: I) -> String {
1618         let mut buf = String::new();
1619         buf.extend(iter);
1620         buf
1621     }
1622 }
1623
1624 #[stable(feature = "extend_string", since = "1.4.0")]
1625 impl FromIterator<String> for String {
1626     fn from_iter<I: IntoIterator<Item = String>>(iter: I) -> String {
1627         let mut buf = String::new();
1628         buf.extend(iter);
1629         buf
1630     }
1631 }
1632
1633 #[stable(feature = "herd_cows", since = "1.19.0")]
1634 impl<'a> FromIterator<Cow<'a, str>> for String {
1635     fn from_iter<I: IntoIterator<Item = Cow<'a, str>>>(iter: I) -> String {
1636         let mut buf = String::new();
1637         buf.extend(iter);
1638         buf
1639     }
1640 }
1641
1642 #[stable(feature = "rust1", since = "1.0.0")]
1643 impl Extend<char> for String {
1644     fn extend<I: IntoIterator<Item = char>>(&mut self, iter: I) {
1645         let iterator = iter.into_iter();
1646         let (lower_bound, _) = iterator.size_hint();
1647         self.reserve(lower_bound);
1648         for ch in iterator {
1649             self.push(ch)
1650         }
1651     }
1652 }
1653
1654 #[stable(feature = "extend_ref", since = "1.2.0")]
1655 impl<'a> Extend<&'a char> for String {
1656     fn extend<I: IntoIterator<Item = &'a char>>(&mut self, iter: I) {
1657         self.extend(iter.into_iter().cloned());
1658     }
1659 }
1660
1661 #[stable(feature = "rust1", since = "1.0.0")]
1662 impl<'a> Extend<&'a str> for String {
1663     fn extend<I: IntoIterator<Item = &'a str>>(&mut self, iter: I) {
1664         for s in iter {
1665             self.push_str(s)
1666         }
1667     }
1668 }
1669
1670 #[stable(feature = "extend_string", since = "1.4.0")]
1671 impl Extend<String> for String {
1672     fn extend<I: IntoIterator<Item = String>>(&mut self, iter: I) {
1673         for s in iter {
1674             self.push_str(&s)
1675         }
1676     }
1677 }
1678
1679 #[stable(feature = "herd_cows", since = "1.19.0")]
1680 impl<'a> Extend<Cow<'a, str>> for String {
1681     fn extend<I: IntoIterator<Item = Cow<'a, str>>>(&mut self, iter: I) {
1682         for s in iter {
1683             self.push_str(&s)
1684         }
1685     }
1686 }
1687
1688 /// A convenience impl that delegates to the impl for `&str`
1689 #[unstable(feature = "pattern",
1690            reason = "API not fully fleshed out and ready to be stabilized",
1691            issue = "27721")]
1692 impl<'a, 'b> Pattern<'a> for &'b String {
1693     type Searcher = <&'b str as Pattern<'a>>::Searcher;
1694
1695     fn into_searcher(self, haystack: &'a str) -> <&'b str as Pattern<'a>>::Searcher {
1696         self[..].into_searcher(haystack)
1697     }
1698
1699     #[inline]
1700     fn is_contained_in(self, haystack: &'a str) -> bool {
1701         self[..].is_contained_in(haystack)
1702     }
1703
1704     #[inline]
1705     fn is_prefix_of(self, haystack: &'a str) -> bool {
1706         self[..].is_prefix_of(haystack)
1707     }
1708 }
1709
1710 #[stable(feature = "rust1", since = "1.0.0")]
1711 impl PartialEq for String {
1712     #[inline]
1713     fn eq(&self, other: &String) -> bool {
1714         PartialEq::eq(&self[..], &other[..])
1715     }
1716     #[inline]
1717     fn ne(&self, other: &String) -> bool {
1718         PartialEq::ne(&self[..], &other[..])
1719     }
1720 }
1721
1722 macro_rules! impl_eq {
1723     ($lhs:ty, $rhs: ty) => {
1724         #[stable(feature = "rust1", since = "1.0.0")]
1725         impl<'a, 'b> PartialEq<$rhs> for $lhs {
1726             #[inline]
1727             fn eq(&self, other: &$rhs) -> bool { PartialEq::eq(&self[..], &other[..]) }
1728             #[inline]
1729             fn ne(&self, other: &$rhs) -> bool { PartialEq::ne(&self[..], &other[..]) }
1730         }
1731
1732         #[stable(feature = "rust1", since = "1.0.0")]
1733         impl<'a, 'b> PartialEq<$lhs> for $rhs {
1734             #[inline]
1735             fn eq(&self, other: &$lhs) -> bool { PartialEq::eq(&self[..], &other[..]) }
1736             #[inline]
1737             fn ne(&self, other: &$lhs) -> bool { PartialEq::ne(&self[..], &other[..]) }
1738         }
1739
1740     }
1741 }
1742
1743 impl_eq! { String, str }
1744 impl_eq! { String, &'a str }
1745 impl_eq! { Cow<'a, str>, str }
1746 impl_eq! { Cow<'a, str>, &'b str }
1747 impl_eq! { Cow<'a, str>, String }
1748
1749 #[stable(feature = "rust1", since = "1.0.0")]
1750 impl Default for String {
1751     /// Creates an empty `String`.
1752     #[inline]
1753     fn default() -> String {
1754         String::new()
1755     }
1756 }
1757
1758 #[stable(feature = "rust1", since = "1.0.0")]
1759 impl fmt::Display for String {
1760     #[inline]
1761     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1762         fmt::Display::fmt(&**self, f)
1763     }
1764 }
1765
1766 #[stable(feature = "rust1", since = "1.0.0")]
1767 impl fmt::Debug for String {
1768     #[inline]
1769     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1770         fmt::Debug::fmt(&**self, f)
1771     }
1772 }
1773
1774 #[stable(feature = "rust1", since = "1.0.0")]
1775 impl hash::Hash for String {
1776     #[inline]
1777     fn hash<H: hash::Hasher>(&self, hasher: &mut H) {
1778         (**self).hash(hasher)
1779     }
1780 }
1781
1782 /// Implements the `+` operator for concatenating two strings.
1783 ///
1784 /// This consumes the `String` on the left-hand side and re-uses its buffer (growing it if
1785 /// necessary). This is done to avoid allocating a new `String` and copying the entire contents on
1786 /// every operation, which would lead to `O(n^2)` running time when building an `n`-byte string by
1787 /// repeated concatenation.
1788 ///
1789 /// The string on the right-hand side is only borrowed; its contents are copied into the returned
1790 /// `String`.
1791 ///
1792 /// # Examples
1793 ///
1794 /// Concatenating two `String`s takes the first by value and borrows the second:
1795 ///
1796 /// ```
1797 /// let a = String::from("hello");
1798 /// let b = String::from(" world");
1799 /// let c = a + &b;
1800 /// // `a` is moved and can no longer be used here.
1801 /// ```
1802 ///
1803 /// If you want to keep using the first `String`, you can clone it and append to the clone instead:
1804 ///
1805 /// ```
1806 /// let a = String::from("hello");
1807 /// let b = String::from(" world");
1808 /// let c = a.clone() + &b;
1809 /// // `a` is still valid here.
1810 /// ```
1811 ///
1812 /// Concatenating `&str` slices can be done by converting the first to a `String`:
1813 ///
1814 /// ```
1815 /// let a = "hello";
1816 /// let b = " world";
1817 /// let c = a.to_string() + b;
1818 /// ```
1819 #[stable(feature = "rust1", since = "1.0.0")]
1820 impl<'a> Add<&'a str> for String {
1821     type Output = String;
1822
1823     #[inline]
1824     fn add(mut self, other: &str) -> String {
1825         self.push_str(other);
1826         self
1827     }
1828 }
1829
1830 /// Implements the `+=` operator for appending to a `String`.
1831 ///
1832 /// This has the same behavior as the [`push_str`] method.
1833 ///
1834 /// [`push_str`]: struct.String.html#method.push_str
1835 #[stable(feature = "stringaddassign", since = "1.12.0")]
1836 impl<'a> AddAssign<&'a str> for String {
1837     #[inline]
1838     fn add_assign(&mut self, other: &str) {
1839         self.push_str(other);
1840     }
1841 }
1842
1843 #[stable(feature = "rust1", since = "1.0.0")]
1844 impl ops::Index<ops::Range<usize>> for String {
1845     type Output = str;
1846
1847     #[inline]
1848     fn index(&self, index: ops::Range<usize>) -> &str {
1849         &self[..][index]
1850     }
1851 }
1852 #[stable(feature = "rust1", since = "1.0.0")]
1853 impl ops::Index<ops::RangeTo<usize>> for String {
1854     type Output = str;
1855
1856     #[inline]
1857     fn index(&self, index: ops::RangeTo<usize>) -> &str {
1858         &self[..][index]
1859     }
1860 }
1861 #[stable(feature = "rust1", since = "1.0.0")]
1862 impl ops::Index<ops::RangeFrom<usize>> for String {
1863     type Output = str;
1864
1865     #[inline]
1866     fn index(&self, index: ops::RangeFrom<usize>) -> &str {
1867         &self[..][index]
1868     }
1869 }
1870 #[stable(feature = "rust1", since = "1.0.0")]
1871 impl ops::Index<ops::RangeFull> for String {
1872     type Output = str;
1873
1874     #[inline]
1875     fn index(&self, _index: ops::RangeFull) -> &str {
1876         unsafe { str::from_utf8_unchecked(&self.vec) }
1877     }
1878 }
1879 #[unstable(feature = "inclusive_range", reason = "recently added, follows RFC", issue = "28237")]
1880 impl ops::Index<ops::RangeInclusive<usize>> for String {
1881     type Output = str;
1882
1883     #[inline]
1884     fn index(&self, index: ops::RangeInclusive<usize>) -> &str {
1885         Index::index(&**self, index)
1886     }
1887 }
1888 #[unstable(feature = "inclusive_range", reason = "recently added, follows RFC", issue = "28237")]
1889 impl ops::Index<ops::RangeToInclusive<usize>> for String {
1890     type Output = str;
1891
1892     #[inline]
1893     fn index(&self, index: ops::RangeToInclusive<usize>) -> &str {
1894         Index::index(&**self, index)
1895     }
1896 }
1897
1898 #[stable(feature = "derefmut_for_string", since = "1.3.0")]
1899 impl ops::IndexMut<ops::Range<usize>> for String {
1900     #[inline]
1901     fn index_mut(&mut self, index: ops::Range<usize>) -> &mut str {
1902         &mut self[..][index]
1903     }
1904 }
1905 #[stable(feature = "derefmut_for_string", since = "1.3.0")]
1906 impl ops::IndexMut<ops::RangeTo<usize>> for String {
1907     #[inline]
1908     fn index_mut(&mut self, index: ops::RangeTo<usize>) -> &mut str {
1909         &mut self[..][index]
1910     }
1911 }
1912 #[stable(feature = "derefmut_for_string", since = "1.3.0")]
1913 impl ops::IndexMut<ops::RangeFrom<usize>> for String {
1914     #[inline]
1915     fn index_mut(&mut self, index: ops::RangeFrom<usize>) -> &mut str {
1916         &mut self[..][index]
1917     }
1918 }
1919 #[stable(feature = "derefmut_for_string", since = "1.3.0")]
1920 impl ops::IndexMut<ops::RangeFull> for String {
1921     #[inline]
1922     fn index_mut(&mut self, _index: ops::RangeFull) -> &mut str {
1923         unsafe { str::from_utf8_unchecked_mut(&mut *self.vec) }
1924     }
1925 }
1926 #[unstable(feature = "inclusive_range", reason = "recently added, follows RFC", issue = "28237")]
1927 impl ops::IndexMut<ops::RangeInclusive<usize>> for String {
1928     #[inline]
1929     fn index_mut(&mut self, index: ops::RangeInclusive<usize>) -> &mut str {
1930         IndexMut::index_mut(&mut **self, index)
1931     }
1932 }
1933 #[unstable(feature = "inclusive_range", reason = "recently added, follows RFC", issue = "28237")]
1934 impl ops::IndexMut<ops::RangeToInclusive<usize>> for String {
1935     #[inline]
1936     fn index_mut(&mut self, index: ops::RangeToInclusive<usize>) -> &mut str {
1937         IndexMut::index_mut(&mut **self, index)
1938     }
1939 }
1940
1941 #[stable(feature = "rust1", since = "1.0.0")]
1942 impl ops::Deref for String {
1943     type Target = str;
1944
1945     #[inline]
1946     fn deref(&self) -> &str {
1947         unsafe { str::from_utf8_unchecked(&self.vec) }
1948     }
1949 }
1950
1951 #[stable(feature = "derefmut_for_string", since = "1.3.0")]
1952 impl ops::DerefMut for String {
1953     #[inline]
1954     fn deref_mut(&mut self) -> &mut str {
1955         unsafe { str::from_utf8_unchecked_mut(&mut *self.vec) }
1956     }
1957 }
1958
1959 /// An error when parsing a `String`.
1960 ///
1961 /// This `enum` is slightly awkward: it will never actually exist. This error is
1962 /// part of the type signature of the implementation of [`FromStr`] on
1963 /// [`String`]. The return type of [`from_str`], requires that an error be
1964 /// defined, but, given that a [`String`] can always be made into a new
1965 /// [`String`] without error, this type will never actually be returned. As
1966 /// such, it is only here to satisfy said signature, and is useless otherwise.
1967 ///
1968 /// [`FromStr`]: ../../std/str/trait.FromStr.html
1969 /// [`String`]: struct.String.html
1970 /// [`from_str`]: ../../std/str/trait.FromStr.html#tymethod.from_str
1971 #[stable(feature = "str_parse_error", since = "1.5.0")]
1972 #[derive(Copy)]
1973 pub enum ParseError {}
1974
1975 #[stable(feature = "rust1", since = "1.0.0")]
1976 impl FromStr for String {
1977     type Err = ParseError;
1978     #[inline]
1979     fn from_str(s: &str) -> Result<String, ParseError> {
1980         Ok(String::from(s))
1981     }
1982 }
1983
1984 #[stable(feature = "str_parse_error", since = "1.5.0")]
1985 impl Clone for ParseError {
1986     fn clone(&self) -> ParseError {
1987         match *self {}
1988     }
1989 }
1990
1991 #[stable(feature = "str_parse_error", since = "1.5.0")]
1992 impl fmt::Debug for ParseError {
1993     fn fmt(&self, _: &mut fmt::Formatter) -> fmt::Result {
1994         match *self {}
1995     }
1996 }
1997
1998 #[stable(feature = "str_parse_error2", since = "1.8.0")]
1999 impl fmt::Display for ParseError {
2000     fn fmt(&self, _: &mut fmt::Formatter) -> fmt::Result {
2001         match *self {}
2002     }
2003 }
2004
2005 #[stable(feature = "str_parse_error", since = "1.5.0")]
2006 impl PartialEq for ParseError {
2007     fn eq(&self, _: &ParseError) -> bool {
2008         match *self {}
2009     }
2010 }
2011
2012 #[stable(feature = "str_parse_error", since = "1.5.0")]
2013 impl Eq for ParseError {}
2014
2015 /// A trait for converting a value to a `String`.
2016 ///
2017 /// This trait is automatically implemented for any type which implements the
2018 /// [`Display`] trait. As such, `ToString` shouldn't be implemented directly:
2019 /// [`Display`] should be implemented instead, and you get the `ToString`
2020 /// implementation for free.
2021 ///
2022 /// [`Display`]: ../../std/fmt/trait.Display.html
2023 #[stable(feature = "rust1", since = "1.0.0")]
2024 pub trait ToString {
2025     /// Converts the given value to a `String`.
2026     ///
2027     /// # Examples
2028     ///
2029     /// Basic usage:
2030     ///
2031     /// ```
2032     /// let i = 5;
2033     /// let five = String::from("5");
2034     ///
2035     /// assert_eq!(five, i.to_string());
2036     /// ```
2037     #[stable(feature = "rust1", since = "1.0.0")]
2038     fn to_string(&self) -> String;
2039 }
2040
2041 /// # Panics
2042 ///
2043 /// In this implementation, the `to_string` method panics
2044 /// if the `Display` implementation returns an error.
2045 /// This indicates an incorrect `Display` implementation
2046 /// since `fmt::Write for String` never returns an error itself.
2047 #[stable(feature = "rust1", since = "1.0.0")]
2048 impl<T: fmt::Display + ?Sized> ToString for T {
2049     #[inline]
2050     default fn to_string(&self) -> String {
2051         use core::fmt::Write;
2052         let mut buf = String::new();
2053         buf.write_fmt(format_args!("{}", self))
2054            .expect("a Display implementation return an error unexpectedly");
2055         buf.shrink_to_fit();
2056         buf
2057     }
2058 }
2059
2060 #[stable(feature = "str_to_string_specialization", since = "1.9.0")]
2061 impl ToString for str {
2062     #[inline]
2063     fn to_string(&self) -> String {
2064         String::from(self)
2065     }
2066 }
2067
2068 #[stable(feature = "cow_str_to_string_specialization", since = "1.17.0")]
2069 impl<'a> ToString for Cow<'a, str> {
2070     #[inline]
2071     fn to_string(&self) -> String {
2072         self[..].to_owned()
2073     }
2074 }
2075
2076 #[stable(feature = "string_to_string_specialization", since = "1.17.0")]
2077 impl ToString for String {
2078     #[inline]
2079     fn to_string(&self) -> String {
2080         self.to_owned()
2081     }
2082 }
2083
2084 #[stable(feature = "rust1", since = "1.0.0")]
2085 impl AsRef<str> for String {
2086     #[inline]
2087     fn as_ref(&self) -> &str {
2088         self
2089     }
2090 }
2091
2092 #[stable(feature = "rust1", since = "1.0.0")]
2093 impl AsRef<[u8]> for String {
2094     #[inline]
2095     fn as_ref(&self) -> &[u8] {
2096         self.as_bytes()
2097     }
2098 }
2099
2100 #[stable(feature = "rust1", since = "1.0.0")]
2101 impl<'a> From<&'a str> for String {
2102     fn from(s: &'a str) -> String {
2103         s.to_owned()
2104     }
2105 }
2106
2107 // note: test pulls in libstd, which causes errors here
2108 #[cfg(not(test))]
2109 #[stable(feature = "string_from_box", since = "1.18.0")]
2110 impl From<Box<str>> for String {
2111     fn from(s: Box<str>) -> String {
2112         s.into_string()
2113     }
2114 }
2115
2116 #[stable(feature = "box_from_str", since = "1.20.0")]
2117 impl From<String> for Box<str> {
2118     fn from(s: String) -> Box<str> {
2119         s.into_boxed_str()
2120     }
2121 }
2122
2123 #[stable(feature = "string_from_cow_str", since = "1.14.0")]
2124 impl<'a> From<Cow<'a, str>> for String {
2125     fn from(s: Cow<'a, str>) -> String {
2126         s.into_owned()
2127     }
2128 }
2129
2130 #[stable(feature = "rust1", since = "1.0.0")]
2131 impl<'a> From<&'a str> for Cow<'a, str> {
2132     #[inline]
2133     fn from(s: &'a str) -> Cow<'a, str> {
2134         Cow::Borrowed(s)
2135     }
2136 }
2137
2138 #[stable(feature = "rust1", since = "1.0.0")]
2139 impl<'a> From<String> for Cow<'a, str> {
2140     #[inline]
2141     fn from(s: String) -> Cow<'a, str> {
2142         Cow::Owned(s)
2143     }
2144 }
2145
2146 #[stable(feature = "cow_str_from_iter", since = "1.12.0")]
2147 impl<'a> FromIterator<char> for Cow<'a, str> {
2148     fn from_iter<I: IntoIterator<Item = char>>(it: I) -> Cow<'a, str> {
2149         Cow::Owned(FromIterator::from_iter(it))
2150     }
2151 }
2152
2153 #[stable(feature = "cow_str_from_iter", since = "1.12.0")]
2154 impl<'a, 'b> FromIterator<&'b str> for Cow<'a, str> {
2155     fn from_iter<I: IntoIterator<Item = &'b str>>(it: I) -> Cow<'a, str> {
2156         Cow::Owned(FromIterator::from_iter(it))
2157     }
2158 }
2159
2160 #[stable(feature = "cow_str_from_iter", since = "1.12.0")]
2161 impl<'a> FromIterator<String> for Cow<'a, str> {
2162     fn from_iter<I: IntoIterator<Item = String>>(it: I) -> Cow<'a, str> {
2163         Cow::Owned(FromIterator::from_iter(it))
2164     }
2165 }
2166
2167 #[stable(feature = "from_string_for_vec_u8", since = "1.14.0")]
2168 impl From<String> for Vec<u8> {
2169     fn from(string: String) -> Vec<u8> {
2170         string.into_bytes()
2171     }
2172 }
2173
2174 #[stable(feature = "rust1", since = "1.0.0")]
2175 impl fmt::Write for String {
2176     #[inline]
2177     fn write_str(&mut self, s: &str) -> fmt::Result {
2178         self.push_str(s);
2179         Ok(())
2180     }
2181
2182     #[inline]
2183     fn write_char(&mut self, c: char) -> fmt::Result {
2184         self.push(c);
2185         Ok(())
2186     }
2187 }
2188
2189 /// A draining iterator for `String`.
2190 ///
2191 /// This struct is created by the [`drain`] method on [`String`]. See its
2192 /// documentation for more.
2193 ///
2194 /// [`drain`]: struct.String.html#method.drain
2195 /// [`String`]: struct.String.html
2196 #[stable(feature = "drain", since = "1.6.0")]
2197 pub struct Drain<'a> {
2198     /// Will be used as &'a mut String in the destructor
2199     string: *mut String,
2200     /// Start of part to remove
2201     start: usize,
2202     /// End of part to remove
2203     end: usize,
2204     /// Current remaining range to remove
2205     iter: Chars<'a>,
2206 }
2207
2208 #[stable(feature = "collection_debug", since = "1.17.0")]
2209 impl<'a> fmt::Debug for Drain<'a> {
2210     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
2211         f.pad("Drain { .. }")
2212     }
2213 }
2214
2215 #[stable(feature = "drain", since = "1.6.0")]
2216 unsafe impl<'a> Sync for Drain<'a> {}
2217 #[stable(feature = "drain", since = "1.6.0")]
2218 unsafe impl<'a> Send for Drain<'a> {}
2219
2220 #[stable(feature = "drain", since = "1.6.0")]
2221 impl<'a> Drop for Drain<'a> {
2222     fn drop(&mut self) {
2223         unsafe {
2224             // Use Vec::drain. "Reaffirm" the bounds checks to avoid
2225             // panic code being inserted again.
2226             let self_vec = (*self.string).as_mut_vec();
2227             if self.start <= self.end && self.end <= self_vec.len() {
2228                 self_vec.drain(self.start..self.end);
2229             }
2230         }
2231     }
2232 }
2233
2234 #[stable(feature = "drain", since = "1.6.0")]
2235 impl<'a> Iterator for Drain<'a> {
2236     type Item = char;
2237
2238     #[inline]
2239     fn next(&mut self) -> Option<char> {
2240         self.iter.next()
2241     }
2242
2243     fn size_hint(&self) -> (usize, Option<usize>) {
2244         self.iter.size_hint()
2245     }
2246 }
2247
2248 #[stable(feature = "drain", since = "1.6.0")]
2249 impl<'a> DoubleEndedIterator for Drain<'a> {
2250     #[inline]
2251     fn next_back(&mut self) -> Option<char> {
2252         self.iter.next_back()
2253     }
2254 }
2255
2256 #[unstable(feature = "fused", issue = "35602")]
2257 impl<'a> FusedIterator for Drain<'a> {}