src/libcollections/string.rs - third_party/rust - Git at Google

 // Copyright 2014 The Rust Project Developers. See the COPYRIGHT
 // file at the top-level directory of this distribution and at
 // http://rust-lang.org/COPYRIGHT.
 //
 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.

 //! A UTF-8 encoded, growable string.
 //!
 //! This module contains the [`String`] type, a trait for converting
 //! [`ToString`]s, and several error types that may result from working with
 //! [`String`]s.
 //!
 //! [`String`]: struct.String.html
 //! [`ToString`]: trait.ToString.html
 //!
 //! # Examples
 //!
 //! There are multiple ways to create a new `String` from a string literal:
 //!
 //! ```rust
 //! let s = "Hello".to_string();
 //!
 //! let s = String::from("world");
 //! let s: String = "also this".into();
 //! ```
 //!
 //! You can create a new `String` from an existing one by concatenating with
 //! `+`:
 //!
 //! ```rust
 //! let s = "Hello".to_string();
 //!
 //! let message = s + " world!";
 //! ```
 //!
 //! If you have a vector of valid UTF-8 bytes, you can make a `String` out of
 //! it. You can do the reverse too.
 //!
 //! ```rust
 //! let sparkle_heart = vec![240, 159, 146, 150];
 //!
 //! // We know these bytes are valid, so we'll use `unwrap()`.
 //! let sparkle_heart = String::from_utf8(sparkle_heart).unwrap();
 //!
 //! assert_eq!("💖", sparkle_heart);
 //!
 //! let bytes = sparkle_heart.into_bytes();
 //!
 //! assert_eq!(bytes, [240, 159, 146, 150]);
 //! ```

 #![stable(feature = "rust1", since = "1.0.0")]

 use core::fmt;
 use core::hash;
 use core::iter::FromIterator;
 use core::mem;
 use core::ops::{self, Add, AddAssign, Index, IndexMut};
 use core::ptr;
 use core::str::pattern::Pattern;
 use rustc_unicode::char::{decode_utf16, REPLACEMENT_CHARACTER};
 use rustc_unicode::str as unicode_str;

 use borrow::{Cow, ToOwned};
 use range::RangeArgument;
 use str::{self, FromStr, Utf8Error, Chars};
 use vec::Vec;
 use boxed::Box;

 /// A UTF-8 encoded, growable string.
 ///
 /// The `String` type is the most common string type that has ownership over the
 /// contents of the string. It has a close relationship with its borrowed
 /// counterpart, the primitive [`str`].
 ///
 /// [`str`]: ../../std/primitive.str.html
 ///
 /// # Examples
 ///
 /// You can create a `String` from a literal string with `String::from`:
 ///
 /// ```
 /// let hello = String::from("Hello, world!");
 /// ```
 ///
 /// You can append a [`char`] to a `String` with the [`push()`] method, and
 /// append a [`&str`] with the [`push_str()`] method:
 ///
 /// ```
 /// let mut hello = String::from("Hello, ");
 ///
 /// hello.push('w');
 /// hello.push_str("orld!");
 /// ```
 ///
 /// [`char`]: ../../std/primitive.char.html
 /// [`push()`]: #method.push
 /// [`push_str()`]: #method.push_str
 ///
 /// If you have a vector of UTF-8 bytes, you can create a `String` from it with
 /// the [`from_utf8()`] method:
 ///
 /// ```
 /// // some bytes, in a vector
 /// let sparkle_heart = vec![240, 159, 146, 150];
 ///
 /// // We know these bytes are valid, so we'll use `unwrap()`.
 /// let sparkle_heart = String::from_utf8(sparkle_heart).unwrap();
 ///
 /// assert_eq!("💖", sparkle_heart);
 /// ```
 ///
 /// [`from_utf8()`]: #method.from_utf8
 ///
 /// # UTF-8
 ///
 /// `String`s are always valid UTF-8. This has a few implications, the first of
 /// which is that if you need a non-UTF-8 string, consider [`OsString`]. It is
 /// similar, but without the UTF-8 constraint. The second implication is that
 /// you cannot index into a `String`:
 ///
 /// ```ignore
 /// let s = "hello";
 ///
 /// println!("The first letter of s is {}", s[0]); // ERROR!!!
 /// ```
 ///
 /// [`OsString`]: ../../std/ffi/struct.OsString.html
 ///
 /// Indexing is intended to be a constant-time operation, but UTF-8 encoding
 /// does not allow us to do this. Furtheremore, it's not clear what sort of
 /// thing the index should return: a byte, a codepoint, or a grapheme cluster.
 /// The [`as_bytes()`] and [`chars()`] methods return iterators over the first
 /// two, respectively.
 ///
 /// [`as_bytes()`]: #method.as_bytes
 /// [`chars()`]: #method.chars
 ///
 /// # Deref
 ///
 /// `String`s implement [`Deref`]`<Target=str>`, and so inherit all of [`str`]'s
 /// methods. In addition, this means that you can pass a `String` to any
 /// function which takes a [`&str`] by using an ampersand (`&`):
 ///
 /// ```
 /// fn takes_str(s: &str) { }
 ///
 /// let s = String::from("Hello");
 ///
 /// takes_str(&s);
 /// ```
 ///
 /// [`&str`]: ../../std/primitive.str.html
 /// [`Deref`]: ../../std/ops/trait.Deref.html
 ///
 /// This will create a [`&str`] from the `String` and pass it in. This
 /// conversion is very inexpensive, and so generally, functions will accept
 /// [`&str`]s as arguments unless they need a `String` for some specific reason.
 ///
 ///
 /// # Representation
 ///
 /// A `String` is made up of three components: a pointer to some bytes, a
 /// length, and a capacity. The pointer points to an internal buffer `String`
 /// uses to store its data. The length is the number of bytes currently stored
 /// in the buffer, and the capacity is the size of the buffer in bytes. As such,
 /// the length will always be less than or equal to the capacity.
 ///
 /// This buffer is always stored on the heap.
 ///
 /// You can look at these with the [`as_ptr()`], [`len()`], and [`capacity()`]
 /// methods:
 ///
 /// ```
 /// use std::mem;
 ///
 /// let story = String::from("Once upon a time...");
 ///
 /// let ptr = story.as_ptr();
 /// let len = story.len();
 /// let capacity = story.capacity();
 ///
 /// // story has nineteen bytes
 /// assert_eq!(19, len);
 ///
 /// // Now that we have our parts, we throw the story away.
 /// mem::forget(story);
 ///
 /// // We can re-build a String out of ptr, len, and capacity. This is all
 /// // unsafe because we are responsible for making sure the components are
 /// // valid:
 /// let s = unsafe { String::from_raw_parts(ptr as *mut _, len, capacity) } ;
 ///
 /// assert_eq!(String::from("Once upon a time..."), s);
 /// ```
 ///
 /// [`as_ptr()`]: #method.as_ptr
 /// [`len()`]: #method.len
 /// [`capacity()`]: #method.capacity
 ///
 /// If a `String` has enough capacity, adding elements to it will not
 /// re-allocate. For example, consider this program:
 ///
 /// ```
 /// let mut s = String::new();
 ///
 /// println!("{}", s.capacity());
 ///
 /// for _ in 0..5 {
 ///     s.push_str("hello");
 ///     println!("{}", s.capacity());
 /// }
 /// ```
 ///
 /// This will output the following:
 ///
 /// ```text
 /// 0
 /// 5
 /// 10
 /// 20
 /// 20
 /// 40
 /// ```
 ///
 /// At first, we have no memory allocated at all, but as we append to the
 /// string, it increases its capacity appropriately. If we instead use the
 /// [`with_capacity()`] method to allocate the correct capacity initially:
 ///
 /// ```
 /// let mut s = String::with_capacity(25);
 ///
 /// println!("{}", s.capacity());
 ///
 /// for _ in 0..5 {
 ///     s.push_str("hello");
 ///     println!("{}", s.capacity());
 /// }
 /// ```
 ///
 /// [`with_capacity()`]: #method.with_capacity
 ///
 /// We end up with a different output:
 ///
 /// ```text
 /// 25
 /// 25
 /// 25
 /// 25
 /// 25
 /// 25
 /// ```
 ///
 /// Here, there's no need to allocate more memory inside the loop.
 #[derive(PartialOrd, Eq, Ord)]
 #[stable(feature = "rust1", since = "1.0.0")]
 pub struct String {
     vec: Vec<u8>,
 }

 /// A possible error value when converting a `String` from a UTF-8 byte vector.
 ///
 /// This type is the error type for the [`from_utf8()`] method on [`String`]. It
 /// is designed in such a way to carefully avoid reallocations: the
 /// [`into_bytes()`] method will give back the byte vector that was used in the
 /// conversion attempt.
 ///
 /// [`from_utf8()`]: struct.String.html#method.from_utf8
 /// [`String`]: struct.String.html
 /// [`into_bytes()`]: struct.FromUtf8Error.html#method.into_bytes
 ///
 /// The [`Utf8Error`] type provided by [`std::str`] represents an error that may
 /// occur when converting a slice of [`u8`]s to a [`&str`]. In this sense, it's
 /// an analogue to `FromUtf8Error`, and you can get one from a `FromUtf8Error`
 /// through the [`utf8_error()`] method.
 ///
 /// [`Utf8Error`]: ../../std/str/struct.Utf8Error.html
 /// [`std::str`]: ../../std/str/index.html
 /// [`u8`]: ../../std/primitive.u8.html
 /// [`&str`]: ../../std/primitive.str.html
 /// [`utf8_error()`]: #method.utf8_error
 ///
 /// # Examples
 ///
 /// Basic usage:
 ///
 /// ```
 /// // some invalid bytes, in a vector
 /// let bytes = vec![0, 159];
 ///
 /// let value = String::from_utf8(bytes);
 ///
 /// assert!(value.is_err());
 /// assert_eq!(vec![0, 159], value.unwrap_err().into_bytes());
 /// ```
 #[stable(feature = "rust1", since = "1.0.0")]
 #[derive(Debug)]
 pub struct FromUtf8Error {
     bytes: Vec<u8>,
     error: Utf8Error,
 }

 /// A possible error value when converting a `String` from a UTF-16 byte slice.
 ///
 /// This type is the error type for the [`from_utf16()`] method on [`String`].
 ///
 /// [`from_utf16()`]: struct.String.html#method.from_utf16
 /// [`String`]: struct.String.html
 ///
 /// # Examples
 ///
 /// Basic usage:
 ///
 /// ```
 /// // 𝄞mu<invalid>ic
 /// let v = &[0xD834, 0xDD1E, 0x006d, 0x0075,
 ///           0xD800, 0x0069, 0x0063];
 ///
 /// assert!(String::from_utf16(v).is_err());
 /// ```
 #[stable(feature = "rust1", since = "1.0.0")]
 #[derive(Debug)]
 pub struct FromUtf16Error(());

 impl String {
     /// Creates a new empty `String`.
     ///
     /// Given that the `String` is empty, this will not allocate any initial
     /// buffer. While that means that this initial operation is very
     /// inexpensive, but may cause excessive allocation later, when you add
     /// data. If you have an idea of how much data the `String` will hold,
     /// consider the [`with_capacity()`] method to prevent excessive
     /// re-allocation.
     ///
     /// [`with_capacity()`]: #method.with_capacity
     ///
     /// # Examples
     ///
     /// Basic usage:
     ///
     /// ```
     /// let s = String::new();
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn new() -> String {
         String { vec: Vec::new() }
     }

     /// Creates a new empty `String` with a particular capacity.
     ///
     /// `String`s have an internal buffer to hold their data. The capacity is
     /// the length of that buffer, and can be queried with the [`capacity()`]
     /// method. This method creates an empty `String`, but one with an initial
     /// buffer that can hold `capacity` bytes. This is useful when you may be
     /// appending a bunch of data to the `String`, reducing the number of
     /// reallocations it needs to do.
     ///
     /// [`capacity()`]: #method.capacity
     ///
     /// If the given capacity is `0`, no allocation will occur, and this method
     /// is identical to the [`new()`] method.
     ///
     /// [`new()`]: #method.new
     ///
     /// # Examples
     ///
     /// Basic usage:
     ///
     /// ```
     /// let mut s = String::with_capacity(10);
     ///
     /// // The String contains no chars, even though it has capacity for more
     /// assert_eq!(s.len(), 0);
     ///
     /// // These are all done without reallocating...
     /// let cap = s.capacity();
     /// for i in 0..10 {
     ///     s.push('a');
     /// }
     ///
     /// assert_eq!(s.capacity(), cap);
     ///
     /// // ...but this may make the vector reallocate
     /// s.push('a');
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn with_capacity(capacity: usize) -> String {
         String { vec: Vec::with_capacity(capacity) }
     }

     // HACK(japaric): with cfg(test) the inherent `[T]::to_vec` method, which is
     // required for this method definition, is not available. Since we don't
     // require this method for testing purposes, I'll just stub it
     // NB see the slice::hack module in slice.rs for more information
     #[inline]
     #[cfg(test)]
     pub fn from_str(_: &str) -> String {
         panic!("not available with cfg(test)");
     }

     /// Converts a vector of bytes to a `String`.
     ///
     /// A string slice ([`&str`]) is made of bytes ([`u8`]), and a vector of bytes
     /// ([`Vec<u8>`]) is made of bytes, so this function converts between the
     /// two. Not all byte slices are valid `String`s, however: `String`
     /// requires that it is valid UTF-8. `from_utf8()` checks to ensure that
     /// the bytes are valid UTF-8, and then does the conversion.
     ///
     /// [`&str`]: ../../std/primitive.str.html
     /// [`u8`]: ../../std/primitive.u8.html
     /// [`Vec<u8>`]: ../../std/vec/struct.Vec.html
     ///
     /// If you are sure that the byte slice is valid UTF-8, and you don't want
     /// to incur the overhead of the validity check, there is an unsafe version
     /// of this function, [`from_utf8_unchecked()`], which has the same behavior
     /// but skips the check.
     ///
     /// [`from_utf8_unchecked()`]: struct.String.html#method.from_utf8_unchecked
     ///
     /// This method will take care to not copy the vector, for efficiency's
     /// sake.
     ///
     /// If you need a `&str` instead of a `String`, consider
     /// [`str::from_utf8()`].
     ///
     /// [`str::from_utf8()`]: ../../std/str/fn.from_utf8.html
     ///
     /// # Errors
     ///
     /// Returns `Err` if the slice is not UTF-8 with a description as to why the
     /// provided bytes are not UTF-8. The vector you moved in is also included.
     ///
     /// # Examples
     ///
     /// Basic usage:
     ///
     /// ```
     /// // some bytes, in a vector
     /// let sparkle_heart = vec![240, 159, 146, 150];
     ///
     /// // We know these bytes are valid, so we'll use `unwrap()`.
     /// let sparkle_heart = String::from_utf8(sparkle_heart).unwrap();
     ///
     /// assert_eq!("💖", sparkle_heart);
     /// ```
     ///
     /// Incorrect bytes:
     ///
     /// ```
     /// // some invalid bytes, in a vector
     /// let sparkle_heart = vec![0, 159, 146, 150];
     ///
     /// assert!(String::from_utf8(sparkle_heart).is_err());
     /// ```
     ///
     /// See the docs for [`FromUtf8Error`] for more details on what you can do
     /// with this error.
     ///
     /// [`FromUtf8Error`]: struct.FromUtf8Error.html
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn from_utf8(vec: Vec<u8>) -> Result<String, FromUtf8Error> {
         match str::from_utf8(&vec) {
             Ok(..) => Ok(String { vec: vec }),
             Err(e) => {
                 Err(FromUtf8Error {
                     bytes: vec,
                     error: e,
                 })
             }
         }
     }

     /// Converts a slice of bytes to a string, including invalid characters.
     ///
     /// Strings are made of bytes ([`u8`]), and a slice of bytes
     /// ([`&[u8]`][byteslice]) is made of bytes, so this function converts
     /// between the two. Not all byte slices are valid strings, however: strings
     /// are required to be valid UTF-8. During this conversion,
     /// `from_utf8_lossy()` will replace any invalid UTF-8 sequences with
     /// `U+FFFD REPLACEMENT CHARACTER`, which looks like this: �
     ///
     /// [`u8`]: ../../std/primitive.u8.html
     /// [byteslice]: ../../std/primitive.slice.html
     ///
     /// If you are sure that the byte slice is valid UTF-8, and you don't want
     /// to incur the overhead of the conversion, there is an unsafe version
     /// of this function, [`from_utf8_unchecked()`], which has the same behavior
     /// but skips the checks.
     ///
     /// [`from_utf8_unchecked()`]: struct.String.html#method.from_utf8_unchecked
     ///
     /// This function returns a [`Cow<'a, str>`]. If our byte slice is invalid
     /// UTF-8, then we need to insert the replacement characters, which will
     /// change the size of the string, and hence, require a `String`. But if
     /// it's already valid UTF-8, we don't need a new allocation. This return
     /// type allows us to handle both cases.
     ///
     /// [`Cow<'a, str>`]: ../../std/borrow/enum.Cow.html
     ///
     /// # Examples
     ///
     /// Basic usage:
     ///
     /// ```
     /// // some bytes, in a vector
     /// let sparkle_heart = vec![240, 159, 146, 150];
     ///
     /// let sparkle_heart = String::from_utf8_lossy(&sparkle_heart);
     ///
     /// assert_eq!("💖", sparkle_heart);
     /// ```
     ///
     /// Incorrect bytes:
     ///
     /// ```
     /// // some invalid bytes
     /// let input = b"Hello \xF0\x90\x80World";
     /// let output = String::from_utf8_lossy(input);
     ///
     /// assert_eq!("Hello �World", output);
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn from_utf8_lossy<'a>(v: &'a [u8]) -> Cow<'a, str> {
         let mut i;
         match str::from_utf8(v) {
             Ok(s) => return Cow::Borrowed(s),
             Err(e) => i = e.valid_up_to(),
         }

         const TAG_CONT_U8: u8 = 128;
         const REPLACEMENT: &'static [u8] = b"\xEF\xBF\xBD"; // U+FFFD in UTF-8
         let total = v.len();
         fn unsafe_get(xs: &[u8], i: usize) -> u8 {
             unsafe { *xs.get_unchecked(i) }
         }
         fn safe_get(xs: &[u8], i: usize, total: usize) -> u8 {
             if i >= total {
                 0
             } else {
                 unsafe_get(xs, i)
             }
         }

         let mut res = String::with_capacity(total);

         if i > 0 {
             unsafe { res.as_mut_vec().extend_from_slice(&v[..i]) };
         }

         // subseqidx is the index of the first byte of the subsequence we're
         // looking at.  It's used to copy a bunch of contiguous good codepoints
         // at once instead of copying them one by one.
         let mut subseqidx = i;

         while i < total {
             let i_ = i;
             let byte = unsafe_get(v, i);
             i += 1;

             macro_rules! error { () => ({
                 unsafe {
                     if subseqidx != i_ {
                         res.as_mut_vec().extend_from_slice(&v[subseqidx..i_]);
                     }
                     subseqidx = i;
                     res.as_mut_vec().extend_from_slice(REPLACEMENT);
                 }
             })}

             if byte < 128 {
                 // subseqidx handles this
             } else {
                 let w = unicode_str::utf8_char_width(byte);

                 match w {
                     2 => {
                         if safe_get(v, i, total) & 192 != TAG_CONT_U8 {
                             error!();
                             continue;
                         }
                         i += 1;
                     }
                     3 => {
                         match (byte, safe_get(v, i, total)) {
                             (0xE0, 0xA0...0xBF) => (),
                             (0xE1...0xEC, 0x80...0xBF) => (),
                             (0xED, 0x80...0x9F) => (),
                             (0xEE...0xEF, 0x80...0xBF) => (),
                             _ => {
                                 error!();
                                 continue;
                             }
                         }
                         i += 1;
                         if safe_get(v, i, total) & 192 != TAG_CONT_U8 {
                             error!();
                             continue;
                         }
                         i += 1;
                     }
                     4 => {
                         match (byte, safe_get(v, i, total)) {
                             (0xF0, 0x90...0xBF) => (),
                             (0xF1...0xF3, 0x80...0xBF) => (),
                             (0xF4, 0x80...0x8F) => (),
                             _ => {
                                 error!();
                                 continue;
                             }
                         }
                         i += 1;
                         if safe_get(v, i, total) & 192 != TAG_CONT_U8 {
                             error!();
                             continue;
                         }
                         i += 1;
                         if safe_get(v, i, total) & 192 != TAG_CONT_U8 {
                             error!();
                             continue;
                         }
                         i += 1;
                     }
                     _ => {
                         error!();
                         continue;
                     }
                 }
             }
         }
         if subseqidx < total {
             unsafe { res.as_mut_vec().extend_from_slice(&v[subseqidx..total]) };
         }
         Cow::Owned(res)
     }

     /// Decode a UTF-16 encoded vector `v` into a `String`, returning `Err`
     /// if `v` contains any invalid data.
     ///
     /// # Examples
     ///
     /// Basic usage:
     ///
     /// ```
     /// // 𝄞music
     /// let v = &[0xD834, 0xDD1E, 0x006d, 0x0075,
     ///           0x0073, 0x0069, 0x0063];
     /// assert_eq!(String::from("𝄞music"),
     ///            String::from_utf16(v).unwrap());
     ///
     /// // 𝄞mu<invalid>ic
     /// let v = &[0xD834, 0xDD1E, 0x006d, 0x0075,
     ///           0xD800, 0x0069, 0x0063];
     /// assert!(String::from_utf16(v).is_err());
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn from_utf16(v: &[u16]) -> Result<String, FromUtf16Error> {
         decode_utf16(v.iter().cloned()).collect::<Result<_, _>>().map_err(|_| FromUtf16Error(()))
     }

     /// Decode a UTF-16 encoded vector `v` into a string, replacing
     /// invalid data with the replacement character (U+FFFD).
     ///
     /// # Examples
     ///
     /// Basic usage:
     ///
     /// ```
     /// // 𝄞mus<invalid>ic<invalid>
     /// let v = &[0xD834, 0xDD1E, 0x006d, 0x0075,
     ///           0x0073, 0xDD1E, 0x0069, 0x0063,
     ///           0xD834];
     ///
     /// assert_eq!(String::from("𝄞mus\u{FFFD}ic\u{FFFD}"),
     ///            String::from_utf16_lossy(v));
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn from_utf16_lossy(v: &[u16]) -> String {
         decode_utf16(v.iter().cloned()).map(|r| r.unwrap_or(REPLACEMENT_CHARACTER)).collect()
     }

     /// Creates a new `String` from a length, capacity, and pointer.
     ///
     /// # Safety
     ///
     /// This is highly unsafe, due to the number of invariants that aren't
     /// checked:
     ///
     /// * The memory at `ptr` needs to have been previously allocated by the
     ///   same allocator the standard library uses.
     /// * `length` needs to be less than or equal to `capacity`.
     /// * `capacity` needs to be the correct value.
     ///
     /// Violating these may cause problems like corrupting the allocator's
     /// internal datastructures.
     ///
     /// The ownership of `ptr` is effectively transferred to the
     /// `String` which may then deallocate, reallocate or change the
     /// contents of memory pointed to by the pointer at will. Ensure
     /// that nothing else uses the pointer after calling this
     /// function.
     ///
     /// # Examples
     ///
     /// Basic usage:
     ///
     /// ```
     /// use std::mem;
     ///
     /// unsafe {
     ///     let s = String::from("hello");
     ///     let ptr = s.as_ptr();
     ///     let len = s.len();
     ///     let capacity = s.capacity();
     ///
     ///     mem::forget(s);
     ///
     ///     let s = String::from_raw_parts(ptr as *mut _, len, capacity);
     ///
     ///     assert_eq!(String::from("hello"), s);
     /// }
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
     pub unsafe fn from_raw_parts(buf: *mut u8, length: usize, capacity: usize) -> String {
         String { vec: Vec::from_raw_parts(buf, length, capacity) }
     }

     /// Converts a vector of bytes to a `String` without checking that the
     /// string contains valid UTF-8.
     ///
     /// See the safe version, [`from_utf8()`], for more details.
     ///
     /// [`from_utf8()`]: struct.String.html#method.from_utf8
     ///
     /// # Safety
     ///
     /// This function is unsafe because it does not check that the bytes passed
     /// to it are valid UTF-8. If this constraint is violated, it may cause
     /// memory unsafety issues with future users of the `String`, as the rest of
     /// the standard library assumes that `String`s are valid UTF-8.
     ///
     /// # Examples
     ///
     /// Basic usage:
     ///
     /// ```
     /// // some bytes, in a vector
     /// let sparkle_heart = vec![240, 159, 146, 150];
     ///
     /// let sparkle_heart = unsafe {
     ///     String::from_utf8_unchecked(sparkle_heart)
     /// };
     ///
     /// assert_eq!("💖", sparkle_heart);
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
     pub unsafe fn from_utf8_unchecked(bytes: Vec<u8>) -> String {
         String { vec: bytes }
     }

     /// Converts a `String` into a byte vector.
     ///
     /// This consumes the `String`, so we do not need to copy its contents.
     ///
     /// # Examples
     ///
     /// Basic usage:
     ///
     /// ```
     /// let s = String::from("hello");
     /// let bytes = s.into_bytes();
     ///
     /// assert_eq!(&[104, 101, 108, 108, 111][..], &bytes[..]);
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn into_bytes(self) -> Vec<u8> {
         self.vec
     }

     /// Extracts a string slice containing the entire string.
     #[inline]
     #[stable(feature = "string_as_str", since = "1.7.0")]
     pub fn as_str(&self) -> &str {
         self
     }

     /// Extracts a string slice containing the entire string.
     #[inline]
     #[stable(feature = "string_as_str", since = "1.7.0")]
     pub fn as_mut_str(&mut self) -> &mut str {
         self
     }

     /// Appends a given string slice onto the end of this `String`.
     ///
     /// # Examples
     ///
     /// Basic usage:
     ///
     /// ```
     /// let mut s = String::from("foo");
     ///
     /// s.push_str("bar");
     ///
     /// assert_eq!("foobar", s);
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn push_str(&mut self, string: &str) {
         self.vec.extend_from_slice(string.as_bytes())
     }

     /// Returns this `String`'s capacity, in bytes.
     ///
     /// # Examples
     ///
     /// Basic usage:
     ///
     /// ```
     /// let s = String::with_capacity(10);
     ///
     /// assert!(s.capacity() >= 10);
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn capacity(&self) -> usize {
         self.vec.capacity()
     }

     /// Ensures that this `String`'s capacity is at least `additional` bytes
     /// larger than its length.
     ///
     /// The capacity may be increased by more than `additional` bytes if it
     /// chooses, to prevent frequent reallocations.
     ///
     /// If you do not want this "at least" behavior, see the [`reserve_exact()`]
     /// method.
     ///
     /// [`reserve_exact()`]: #method.reserve_exact
     ///
     /// # Panics
     ///
     /// Panics if the new capacity overflows `usize`.
     ///
     /// # Examples
     ///
     /// Basic usage:
     ///
     /// ```
     /// let mut s = String::new();
     ///
     /// s.reserve(10);
     ///
     /// assert!(s.capacity() >= 10);
     /// ```
     ///
     /// This may not actually increase the capacity:
     ///
     /// ```
     /// let mut s = String::with_capacity(10);
     /// s.push('a');
     /// s.push('b');
     ///
     /// // s now has a length of 2 and a capacity of 10
     /// assert_eq!(2, s.len());
     /// assert_eq!(10, s.capacity());
     ///
     /// // Since we already have an extra 8 capacity, calling this...
     /// s.reserve(8);
     ///
     /// // ... doesn't actually increase.
     /// assert_eq!(10, s.capacity());
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn reserve(&mut self, additional: usize) {
         self.vec.reserve(additional)
     }

     /// Ensures that this `String`'s capacity is `additional` bytes
     /// larger than its length.
     ///
     /// Consider using the [`reserve()`] method unless you absolutely know
     /// better than the allocator.
     ///
     /// [`reserve()`]: #method.reserve
     ///
     /// # Panics
     ///
     /// Panics if the new capacity overflows `usize`.
     ///
     /// # Examples
     ///
     /// Basic usage:
     ///
     /// ```
     /// let mut s = String::new();
     ///
     /// s.reserve_exact(10);
     ///
     /// assert!(s.capacity() >= 10);
     /// ```
     ///
     /// This may not actually increase the capacity:
     ///
     /// ```
     /// let mut s = String::with_capacity(10);
     /// s.push('a');
     /// s.push('b');
     ///
     /// // s now has a length of 2 and a capacity of 10
     /// assert_eq!(2, s.len());
     /// assert_eq!(10, s.capacity());
     ///
     /// // Since we already have an extra 8 capacity, calling this...
     /// s.reserve_exact(8);
     ///
     /// // ... doesn't actually increase.
     /// assert_eq!(10, s.capacity());
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn reserve_exact(&mut self, additional: usize) {
         self.vec.reserve_exact(additional)
     }

     /// Shrinks the capacity of this `String` to match its length.
     ///
     /// # Examples
     ///
     /// Basic usage:
     ///
     /// ```
     /// let mut s = String::from("foo");
     ///
     /// s.reserve(100);
     /// assert!(s.capacity() >= 100);
     ///
     /// s.shrink_to_fit();
     /// assert_eq!(3, s.capacity());
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn shrink_to_fit(&mut self) {
         self.vec.shrink_to_fit()
     }

     /// Appends the given `char` to the end of this `String`.
     ///
     /// # Examples
     ///
     /// Basic usage:
     ///
     /// ```
     /// let mut s = String::from("abc");
     ///
     /// s.push('1');
     /// s.push('2');
     /// s.push('3');
     ///
     /// assert_eq!("abc123", s);
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn push(&mut self, ch: char) {
         match ch.len_utf8() {
             1 => self.vec.push(ch as u8),
             _ => self.vec.extend_from_slice(ch.encode_utf8().as_slice()),
         }
     }

     /// Returns a byte slice of this `String`'s contents.
     ///
     /// # Examples
     ///
     /// Basic usage:
     ///
     /// ```
     /// let s = String::from("hello");
     ///
     /// assert_eq!(&[104, 101, 108, 108, 111], s.as_bytes());
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn as_bytes(&self) -> &[u8] {
         &self.vec
     }

     /// Shortens this `String` to the specified length.
     ///
     /// If `new_len` is greater than the string's current length, this has no
     /// effect.
     ///
     /// # Panics
     ///
     /// Panics if `new_len` does not lie on a [`char`] boundary.
     ///
     /// [`char`]: ../../std/primitive.char.html
     ///
     /// # Examples
     ///
     /// Basic usage:
     ///
     /// ```
     /// let mut s = String::from("hello");
     ///
     /// s.truncate(2);
     ///
     /// assert_eq!("he", s);
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn truncate(&mut self, new_len: usize) {
         if new_len <= self.len() {
             assert!(self.is_char_boundary(new_len));
             self.vec.truncate(new_len)
         }
     }

     /// Removes the last character from the string buffer and returns it.
     ///
     /// Returns `None` if this `String` is empty.
     ///
     /// # Examples
     ///
     /// Basic usage:
     ///
     /// ```
     /// let mut s = String::from("foo");
     ///
     /// assert_eq!(s.pop(), Some('o'));
     /// assert_eq!(s.pop(), Some('o'));
     /// assert_eq!(s.pop(), Some('f'));
     ///
     /// assert_eq!(s.pop(), None);
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn pop(&mut self) -> Option<char> {
         let ch = match self.chars().rev().next() {
             Some(ch) => ch,
             None => return None,
         };
         let newlen = self.len() - ch.len_utf8();
         unsafe {
             self.vec.set_len(newlen);
         }
         Some(ch)
     }

     /// Removes a `char` from this `String` at a byte position and returns it.
     ///
     /// This is an `O(n)` operation, as it requires copying every element in the
     /// buffer.
     ///
     /// # Panics
     ///
     /// Panics if `idx` is larger than or equal to the `String`'s length,
     /// or if it does not lie on a [`char`] boundary.
     ///
     /// [`char`]: ../../std/primitive.char.html
     ///
     /// # Examples
     ///
     /// Basic usage:
     ///
     /// ```
     /// let mut s = String::from("foo");
     ///
     /// assert_eq!(s.remove(0), 'f');
     /// assert_eq!(s.remove(1), 'o');
     /// assert_eq!(s.remove(0), 'o');
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn remove(&mut self, idx: usize) -> char {
         let ch = match self[idx..].chars().next() {
             Some(ch) => ch,
             None => panic!("cannot remove a char from the end of a string"),
         };

         let next = idx + ch.len_utf8();
         let len = self.len();
         unsafe {
             ptr::copy(self.vec.as_ptr().offset(next as isize),
                       self.vec.as_mut_ptr().offset(idx as isize),
                       len - next);
             self.vec.set_len(len - (next - idx));
         }
         ch
     }

     /// Inserts a character into this `String` at a byte position.
     ///
     /// This is an `O(n)` operation as it requires copying every element in the
     /// buffer.
     ///
     /// # Panics
     ///
     /// Panics if `idx` is larger than the `String`'s length, or if it does not
     /// lie on a [`char`] boundary.
     ///
     /// [`char`]: ../../std/primitive.char.html
     ///
     /// # Examples
     ///
     /// Basic usage:
     ///
     /// ```
     /// let mut s = String::with_capacity(3);
     ///
     /// s.insert(0, 'f');
     /// s.insert(1, 'o');
     /// s.insert(2, 'o');
     ///
     /// assert_eq!("foo", s);
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn insert(&mut self, idx: usize, ch: char) {
         let len = self.len();
         assert!(idx <= len);
         assert!(self.is_char_boundary(idx));
         let bits = ch.encode_utf8();

         unsafe {
             self.insert_bytes(idx, bits.as_slice());
         }
     }

     unsafe fn insert_bytes(&mut self, idx: usize, bytes: &[u8]) {
         let len = self.len();
         let amt = bytes.len();
         self.vec.reserve(amt);

         ptr::copy(self.vec.as_ptr().offset(idx as isize),
                   self.vec.as_mut_ptr().offset((idx + amt) as isize),
                   len - idx);
         ptr::copy(bytes.as_ptr(),
                   self.vec.as_mut_ptr().offset(idx as isize),
                   amt);
         self.vec.set_len(len + amt);
     }

     /// Inserts a string into this `String` at a byte position.
     ///
     /// This is an `O(n)` operation as it requires copying every element in the
     /// buffer.
     ///
     /// # Panics
     ///
     /// Panics if `idx` is larger than the `String`'s length, or if it does not
     /// lie on a [`char`] boundary.
     ///
     /// [`char`]: ../../std/primitive.char.html
     ///
     /// # Examples
     ///
     /// Basic usage:
     ///
     /// ```
     /// #![feature(insert_str)]
     ///
     /// let mut s = String::from("bar");
     ///
     /// s.insert_str(0, "foo");
     ///
     /// assert_eq!("foobar", s);
     /// ```
     #[inline]
     #[unstable(feature = "insert_str",
                reason = "recent addition",
                issue = "0")]
     pub fn insert_str(&mut self, idx: usize, string: &str) {
         let len = self.len();
         assert!(idx <= len);
         assert!(self.is_char_boundary(idx));

         unsafe {
             self.insert_bytes(idx, string.as_bytes());
         }
     }

     /// Returns a mutable reference to the contents of this `String`.
     ///
     /// # Safety
     ///
     /// This function is unsafe because it does not check that the bytes passed
     /// to it are valid UTF-8. If this constraint is violated, it may cause
     /// memory unsafety issues with future users of the `String`, as the rest of
     /// the standard library assumes that `String`s are valid UTF-8.
     ///
     /// # Examples
     ///
     /// Basic usage:
     ///
     /// ```
     /// let mut s = String::from("hello");
     ///
     /// unsafe {
     ///     let vec = s.as_mut_vec();
     ///     assert_eq!(&[104, 101, 108, 108, 111][..], &vec[..]);
     ///
     ///     vec.reverse();
     /// }
     /// assert_eq!(s, "olleh");
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
     pub unsafe fn as_mut_vec(&mut self) -> &mut Vec<u8> {
         &mut self.vec
     }

     /// Returns the length of this `String`, in bytes.
     ///
     /// # Examples
     ///
     /// Basic usage:
     ///
     /// ```
     /// let a = String::from("foo");
     ///
     /// assert_eq!(a.len(), 3);
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn len(&self) -> usize {
         self.vec.len()
     }

     /// Returns `true` if this `String` has a length of zero.
     ///
     /// Returns `false` otherwise.
     ///
     /// # Examples
     ///
     /// Basic usage:
     ///
     /// ```
     /// let mut v = String::new();
     /// assert!(v.is_empty());
     ///
     /// v.push('a');
     /// assert!(!v.is_empty());
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn is_empty(&self) -> bool {
         self.len() == 0
     }

     /// Truncates this `String`, removing all contents.
     ///
     /// While this means the `String` will have a length of zero, it does not
     /// touch its capacity.
     ///
     /// # Examples
     ///
     /// Basic usage:
     ///
     /// ```
     /// let mut s = String::from("foo");
     ///
     /// s.clear();
     ///
     /// assert!(s.is_empty());
     /// assert_eq!(0, s.len());
     /// assert_eq!(3, s.capacity());
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn clear(&mut self) {
         self.vec.clear()
     }

     /// Create a draining iterator that removes the specified range in the string
     /// and yields the removed chars.
     ///
     /// Note: The element range is removed even if the iterator is not
     /// consumed until the end.
     ///
     /// # Panics
     ///
     /// Panics if the starting point or end point do not lie on a [`char`]
     /// boundary, or if they're out of bounds.
     ///
     /// [`char`]: ../../std/primitive.char.html
     ///
     /// # Examples
     ///
     /// Basic usage:
     ///
     /// ```
     /// let mut s = String::from("α is alpha, β is beta");
     /// let beta_offset = s.find('β').unwrap_or(s.len());
     ///
     /// // Remove the range up until the β from the string
     /// let t: String = s.drain(..beta_offset).collect();
     /// assert_eq!(t, "α is alpha, ");
     /// assert_eq!(s, "β is beta");
     ///
     /// // A full range clears the string
     /// s.drain(..);
     /// assert_eq!(s, "");
     /// ```
     #[stable(feature = "drain", since = "1.6.0")]
     pub fn drain<R>(&mut self, range: R) -> Drain
         where R: RangeArgument<usize>
     {
         // Memory safety
         //
         // The String version of Drain does not have the memory safety issues
         // of the vector version. The data is just plain bytes.
         // Because the range removal happens in Drop, if the Drain iterator is leaked,
         // the removal will not happen.
         let len = self.len();
         let start = *range.start().unwrap_or(&0);
         let end = *range.end().unwrap_or(&len);

         // Take out two simultaneous borrows. The &mut String won't be accessed
         // until iteration is over, in Drop.
         let self_ptr = self as *mut _;
         // slicing does the appropriate bounds checks
         let chars_iter = self[start..end].chars();

         Drain {
             start: start,
             end: end,
             iter: chars_iter,
             string: self_ptr,
         }
     }

     /// Converts this `String` into a `Box<str>`.
     ///
     /// This will drop any excess capacity.
     ///
     /// # Examples
     ///
     /// Basic usage:
     ///
     /// ```
     /// let s = String::from("hello");
     ///
     /// let b = s.into_boxed_str();
     /// ```
     #[stable(feature = "box_str", since = "1.4.0")]
     pub fn into_boxed_str(self) -> Box<str> {
         let slice = self.vec.into_boxed_slice();
         unsafe { mem::transmute::<Box<[u8]>, Box<str>>(slice) }
     }
 }

 impl FromUtf8Error {
     /// Returns the bytes that were attempted to convert to a `String`.
     ///
     /// This method is carefully constructed to avoid allocation. It will
     /// consume the error, moving out the bytes, so that a copy of the bytes
     /// does not need to be made.
     ///
     /// # Examples
     ///
     /// Basic usage:
     ///
     /// ```
     /// // some invalid bytes, in a vector
     /// let bytes = vec![0, 159];
     ///
     /// let value = String::from_utf8(bytes);
     ///
     /// assert_eq!(vec![0, 159], value.unwrap_err().into_bytes());
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn into_bytes(self) -> Vec<u8> {
         self.bytes
     }

     /// Fetch a `Utf8Error` to get more details about the conversion failure.
     ///
     /// The [`Utf8Error`] type provided by [`std::str`] represents an error that may
     /// occur when converting a slice of [`u8`]s to a [`&str`]. In this sense, it's
     /// an analogue to `FromUtf8Error`. See its documentation for more details
     /// on using it.
     ///
     /// [`Utf8Error`]: ../../std/str/struct.Utf8Error.html
     /// [`std::str`]: ../../std/str/index.html
     /// [`u8`]: ../../std/primitive.u8.html
     /// [`&str`]: ../../std/primitive.str.html
     ///
     /// # Examples
     ///
     /// Basic usage:
     ///
     /// ```
     /// // some invalid bytes, in a vector
     /// let bytes = vec![0, 159];
     ///
     /// let error = String::from_utf8(bytes).unwrap_err().utf8_error();
     ///
     /// // the first byte is invalid here
     /// assert_eq!(1, error.valid_up_to());
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn utf8_error(&self) -> Utf8Error {
         self.error
     }
 }

 #[stable(feature = "rust1", since = "1.0.0")]
 impl fmt::Display for FromUtf8Error {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         fmt::Display::fmt(&self.error, f)
     }
 }

 #[stable(feature = "rust1", since = "1.0.0")]
 impl fmt::Display for FromUtf16Error {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         fmt::Display::fmt("invalid utf-16: lone surrogate found", f)
     }
 }

 #[stable(feature = "rust1", since = "1.0.0")]
 impl Clone for String {
     fn clone(&self) -> Self {
         String { vec: self.vec.clone() }
     }

     fn clone_from(&mut self, source: &Self) {
         self.vec.clone_from(&source.vec);
     }
 }

 #[stable(feature = "rust1", since = "1.0.0")]
 impl FromIterator<char> for String {
     fn from_iter<I: IntoIterator<Item = char>>(iter: I) -> String {
         let mut buf = String::new();
         buf.extend(iter);
         buf
     }
 }

 #[stable(feature = "rust1", since = "1.0.0")]
 impl<'a> FromIterator<&'a str> for String {
     fn from_iter<I: IntoIterator<Item = &'a str>>(iter: I) -> String {
         let mut buf = String::new();
         buf.extend(iter);
         buf
     }
 }

 #[stable(feature = "extend_string", since = "1.4.0")]
 impl FromIterator<String> for String {
     fn from_iter<I: IntoIterator<Item = String>>(iter: I) -> String {
         let mut buf = String::new();
         buf.extend(iter);
         buf
     }
 }

 #[stable(feature = "rust1", since = "1.0.0")]
 impl Extend<char> for String {
     fn extend<I: IntoIterator<Item = char>>(&mut self, iter: I) {
         let iterator = iter.into_iter();
         let (lower_bound, _) = iterator.size_hint();
         self.reserve(lower_bound);
         for ch in iterator {
             self.push(ch)
         }
     }
 }

 #[stable(feature = "extend_ref", since = "1.2.0")]
 impl<'a> Extend<&'a char> for String {
     fn extend<I: IntoIterator<Item = &'a char>>(&mut self, iter: I) {
         self.extend(iter.into_iter().cloned());
     }
 }

 #[stable(feature = "rust1", since = "1.0.0")]
 impl<'a> Extend<&'a str> for String {
     fn extend<I: IntoIterator<Item = &'a str>>(&mut self, iter: I) {
         for s in iter {
             self.push_str(s)
         }
     }
 }

 #[stable(feature = "extend_string", since = "1.4.0")]
 impl Extend<String> for String {
     fn extend<I: IntoIterator<Item = String>>(&mut self, iter: I) {
         for s in iter {
             self.push_str(&s)
         }
     }
 }

 /// A convenience impl that delegates to the impl for `&str`
 #[unstable(feature = "pattern",
            reason = "API not fully fleshed out and ready to be stabilized",
            issue = "27721")]
 impl<'a, 'b> Pattern<'a> for &'b String {
     type Searcher = <&'b str as Pattern<'a>>::Searcher;

     fn into_searcher(self, haystack: &'a str) -> <&'b str as Pattern<'a>>::Searcher {
         self[..].into_searcher(haystack)
     }

     #[inline]
     fn is_contained_in(self, haystack: &'a str) -> bool {
         self[..].is_contained_in(haystack)
     }

     #[inline]
     fn is_prefix_of(self, haystack: &'a str) -> bool {
         self[..].is_prefix_of(haystack)
     }
 }

 #[stable(feature = "rust1", since = "1.0.0")]
 impl PartialEq for String {
     #[inline]
     fn eq(&self, other: &String) -> bool {
         PartialEq::eq(&self[..], &other[..])
     }
     #[inline]
     fn ne(&self, other: &String) -> bool {
         PartialEq::ne(&self[..], &other[..])
     }
 }

 macro_rules! impl_eq {
     ($lhs:ty, $rhs: ty) => {
         #[stable(feature = "rust1", since = "1.0.0")]
         impl<'a, 'b> PartialEq<$rhs> for $lhs {
             #[inline]
             fn eq(&self, other: &$rhs) -> bool { PartialEq::eq(&self[..], &other[..]) }
             #[inline]
             fn ne(&self, other: &$rhs) -> bool { PartialEq::ne(&self[..], &other[..]) }
         }

         #[stable(feature = "rust1", since = "1.0.0")]
         impl<'a, 'b> PartialEq<$lhs> for $rhs {
             #[inline]
             fn eq(&self, other: &$lhs) -> bool { PartialEq::eq(&self[..], &other[..]) }
             #[inline]
             fn ne(&self, other: &$lhs) -> bool { PartialEq::ne(&self[..], &other[..]) }
         }

     }
 }

 impl_eq! { String, str }
 impl_eq! { String, &'a str }
 impl_eq! { Cow<'a, str>, str }
 impl_eq! { Cow<'a, str>, &'b str }
 impl_eq! { Cow<'a, str>, String }

 #[stable(feature = "rust1", since = "1.0.0")]
 impl Default for String {
     #[inline]
     fn default() -> String {
         String::new()
     }
 }

 #[stable(feature = "rust1", since = "1.0.0")]
 impl fmt::Display for String {
     #[inline]
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         fmt::Display::fmt(&**self, f)
     }
 }

 #[stable(feature = "rust1", since = "1.0.0")]
 impl fmt::Debug for String {
     #[inline]
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         fmt::Debug::fmt(&**self, f)
     }
 }

 #[stable(feature = "rust1", since = "1.0.0")]
 impl hash::Hash for String {
     #[inline]
     fn hash<H: hash::Hasher>(&self, hasher: &mut H) {
         (**self).hash(hasher)
     }
 }

 #[stable(feature = "rust1", since = "1.0.0")]
 impl<'a> Add<&'a str> for String {
     type Output = String;

     #[inline]
     fn add(mut self, other: &str) -> String {
         self.push_str(other);
         self
     }
 }

 #[stable(feature = "stringaddassign", since = "1.12.0")]
 impl<'a> AddAssign<&'a str> for String {
     #[inline]
     fn add_assign(&mut self, other: &str) {
         self.push_str(other);
     }
 }

 #[stable(feature = "rust1", since = "1.0.0")]
 impl ops::Index<ops::Range<usize>> for String {
     type Output = str;

     #[inline]
     fn index(&self, index: ops::Range<usize>) -> &str {
         &self[..][index]
     }
 }
 #[stable(feature = "rust1", since = "1.0.0")]
 impl ops::Index<ops::RangeTo<usize>> for String {
     type Output = str;

     #[inline]
     fn index(&self, index: ops::RangeTo<usize>) -> &str {
         &self[..][index]
     }
 }
 #[stable(feature = "rust1", since = "1.0.0")]
 impl ops::Index<ops::RangeFrom<usize>> for String {
     type Output = str;

     #[inline]
     fn index(&self, index: ops::RangeFrom<usize>) -> &str {
         &self[..][index]
     }
 }
 #[stable(feature = "rust1", since = "1.0.0")]
 impl ops::Index<ops::RangeFull> for String {
     type Output = str;

     #[inline]
     fn index(&self, _index: ops::RangeFull) -> &str {
         unsafe { str::from_utf8_unchecked(&self.vec) }
     }
 }
 #[unstable(feature = "inclusive_range", reason = "recently added, follows RFC", issue = "28237")]
 impl ops::Index<ops::RangeInclusive<usize>> for String {
     type Output = str;

     #[inline]
     fn index(&self, index: ops::RangeInclusive<usize>) -> &str {
         Index::index(&**self, index)
     }
 }
 #[unstable(feature = "inclusive_range", reason = "recently added, follows RFC", issue = "28237")]
 impl ops::Index<ops::RangeToInclusive<usize>> for String {
     type Output = str;

     #[inline]
     fn index(&self, index: ops::RangeToInclusive<usize>) -> &str {
         Index::index(&**self, index)
     }
 }

 #[stable(feature = "derefmut_for_string", since = "1.2.0")]
 impl ops::IndexMut<ops::Range<usize>> for String {
     #[inline]
     fn index_mut(&mut self, index: ops::Range<usize>) -> &mut str {
         &mut self[..][index]
     }
 }
 #[stable(feature = "derefmut_for_string", since = "1.2.0")]
 impl ops::IndexMut<ops::RangeTo<usize>> for String {
     #[inline]
     fn index_mut(&mut self, index: ops::RangeTo<usize>) -> &mut str {
         &mut self[..][index]
     }
 }
 #[stable(feature = "derefmut_for_string", since = "1.2.0")]
 impl ops::IndexMut<ops::RangeFrom<usize>> for String {
     #[inline]
     fn index_mut(&mut self, index: ops::RangeFrom<usize>) -> &mut str {
         &mut self[..][index]
     }
 }
 #[stable(feature = "derefmut_for_string", since = "1.2.0")]
 impl ops::IndexMut<ops::RangeFull> for String {
     #[inline]
     fn index_mut(&mut self, _index: ops::RangeFull) -> &mut str {
         unsafe { mem::transmute(&mut *self.vec) }
     }
 }
 #[unstable(feature = "inclusive_range", reason = "recently added, follows RFC", issue = "28237")]
 impl ops::IndexMut<ops::RangeInclusive<usize>> for String {
     #[inline]
     fn index_mut(&mut self, index: ops::RangeInclusive<usize>) -> &mut str {
         IndexMut::index_mut(&mut **self, index)
     }
 }
 #[unstable(feature = "inclusive_range", reason = "recently added, follows RFC", issue = "28237")]
 impl ops::IndexMut<ops::RangeToInclusive<usize>> for String {
     #[inline]
     fn index_mut(&mut self, index: ops::RangeToInclusive<usize>) -> &mut str {
         IndexMut::index_mut(&mut **self, index)
     }
 }

 #[stable(feature = "rust1", since = "1.0.0")]
 impl ops::Deref for String {
     type Target = str;

     #[inline]
     fn deref(&self) -> &str {
         unsafe { str::from_utf8_unchecked(&self.vec) }
     }
 }

 #[stable(feature = "derefmut_for_string", since = "1.2.0")]
 impl ops::DerefMut for String {
     #[inline]
     fn deref_mut(&mut self) -> &mut str {
         unsafe { mem::transmute(&mut *self.vec) }
     }
 }

 /// An error when parsing a `String`.
 ///
 /// This `enum` is slightly awkward: it will never actually exist. This error is
 /// part of the type signature of the implementation of [`FromStr`] on
 /// [`String`]. The return type of [`from_str()`], requires that an error be
 /// defined, but, given that a [`String`] can always be made into a new
 /// [`String`] without error, this type will never actually be returned. As
 /// such, it is only here to satisfy said signature, and is useless otherwise.
 ///
 /// [`FromStr`]: ../../std/str/trait.FromStr.html
 /// [`String`]: struct.String.html
 /// [`from_str()`]: ../../std/str/trait.FromStr.html#tymethod.from_str
 #[stable(feature = "str_parse_error", since = "1.5.0")]
 #[derive(Copy)]
 pub enum ParseError {}

 #[stable(feature = "rust1", since = "1.0.0")]
 impl FromStr for String {
     type Err = ParseError;
     #[inline]
     fn from_str(s: &str) -> Result<String, ParseError> {
         Ok(String::from(s))
     }
 }

 #[stable(feature = "str_parse_error", since = "1.5.0")]
 impl Clone for ParseError {
     fn clone(&self) -> ParseError {
         match *self {}
     }
 }

 #[stable(feature = "str_parse_error", since = "1.5.0")]
 impl fmt::Debug for ParseError {
     fn fmt(&self, _: &mut fmt::Formatter) -> fmt::Result {
         match *self {}
     }
 }

 #[stable(feature = "str_parse_error2", since = "1.8.0")]
 impl fmt::Display for ParseError {
     fn fmt(&self, _: &mut fmt::Formatter) -> fmt::Result {
         match *self {}
     }
 }

 #[stable(feature = "str_parse_error", since = "1.5.0")]
 impl PartialEq for ParseError {
     fn eq(&self, _: &ParseError) -> bool {
         match *self {}
     }
 }

 #[stable(feature = "str_parse_error", since = "1.5.0")]
 impl Eq for ParseError {}

 /// A trait for converting a value to a `String`.
 ///
 /// This trait is automatically implemented for any type which implements the
 /// [`Display`] trait. As such, `ToString` shouldn't be implemented directly:
 /// [`Display`] should be implemented instead, and you get the `ToString`
 /// implementation for free.
 ///
 /// [`Display`]: ../../std/fmt/trait.Display.html
 #[stable(feature = "rust1", since = "1.0.0")]
 pub trait ToString {
     /// Converts the given value to a `String`.
     ///
     /// # Examples
     ///
     /// Basic usage:
     ///
     /// ```
     /// let i = 5;
     /// let five = String::from("5");
     ///
     /// assert_eq!(five, i.to_string());
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
     fn to_string(&self) -> String;
 }

 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T: fmt::Display + ?Sized> ToString for T {
     #[inline]
     default fn to_string(&self) -> String {
         use core::fmt::Write;
         let mut buf = String::new();
         let _ = buf.write_fmt(format_args!("{}", self));
         buf.shrink_to_fit();
         buf
     }
 }

 #[stable(feature = "str_to_string_specialization", since = "1.9.0")]
 impl ToString for str {
     #[inline]
     fn to_string(&self) -> String {
         String::from(self)
     }
 }

 #[stable(feature = "rust1", since = "1.0.0")]
 impl AsRef<str> for String {
     #[inline]
     fn as_ref(&self) -> &str {
         self
     }
 }

 #[stable(feature = "rust1", since = "1.0.0")]
 impl AsRef<[u8]> for String {
     #[inline]
     fn as_ref(&self) -> &[u8] {
         self.as_bytes()
     }
 }

 #[stable(feature = "rust1", since = "1.0.0")]
 impl<'a> From<&'a str> for String {
     fn from(s: &'a str) -> String {
         s.to_owned()
     }
 }

 #[stable(feature = "rust1", since = "1.0.0")]
 impl<'a> From<&'a str> for Cow<'a, str> {
     #[inline]
     fn from(s: &'a str) -> Cow<'a, str> {
         Cow::Borrowed(s)
     }
 }

 #[stable(feature = "rust1", since = "1.0.0")]
 impl<'a> From<String> for Cow<'a, str> {
     #[inline]
     fn from(s: String) -> Cow<'a, str> {
         Cow::Owned(s)
     }
 }

 #[stable(feature = "rust1", since = "1.0.0")]
 impl Into<Vec<u8>> for String {
     fn into(self) -> Vec<u8> {
         self.into_bytes()
     }
 }

 #[stable(feature = "stringfromchars", since = "1.12.0")]
 impl<'a> From<&'a [char]> for String {
     #[inline]
     fn from(v: &'a [char]) -> String {
         let mut s = String::with_capacity(v.len());
         for c in v {
             s.push(*c);
         }
         s
     }
 }

 #[stable(feature = "stringfromchars", since = "1.12.0")]
 impl From<Vec<char>> for String {
     #[inline]
     fn from(v: Vec<char>) -> String {
         String::from(v.as_slice())
     }
 }

 #[stable(feature = "rust1", since = "1.0.0")]
 impl fmt::Write for String {
     #[inline]
     fn write_str(&mut self, s: &str) -> fmt::Result {
         self.push_str(s);
         Ok(())
     }

     #[inline]
     fn write_char(&mut self, c: char) -> fmt::Result {
         self.push(c);
         Ok(())
     }
 }

 /// A draining iterator for `String`.
 ///
 /// This struct is created by the [`drain()`] method on [`String`]. See its
 /// documentation for more.
 ///
 /// [`drain()`]: struct.String.html#method.drain
 /// [`String`]: struct.String.html
 #[stable(feature = "drain", since = "1.6.0")]
 pub struct Drain<'a> {
     /// Will be used as &'a mut String in the destructor
     string: *mut String,
     /// Start of part to remove
     start: usize,
     /// End of part to remove
     end: usize,
     /// Current remaining range to remove
     iter: Chars<'a>,
 }

 #[stable(feature = "drain", since = "1.6.0")]
 unsafe impl<'a> Sync for Drain<'a> {}
 #[stable(feature = "drain", since = "1.6.0")]
 unsafe impl<'a> Send for Drain<'a> {}

 #[stable(feature = "drain", since = "1.6.0")]
 impl<'a> Drop for Drain<'a> {
     fn drop(&mut self) {
         unsafe {
             // Use Vec::drain. "Reaffirm" the bounds checks to avoid
             // panic code being inserted again.
             let self_vec = (*self.string).as_mut_vec();
             if self.start <= self.end && self.end <= self_vec.len() {
                 self_vec.drain(self.start..self.end);
             }
         }
     }
 }

 #[stable(feature = "drain", since = "1.6.0")]
 impl<'a> Iterator for Drain<'a> {
     type Item = char;

     #[inline]
     fn next(&mut self) -> Option<char> {
         self.iter.next()
     }

     fn size_hint(&self) -> (usize, Option<usize>) {
         self.iter.size_hint()
     }
 }

 #[stable(feature = "drain", since = "1.6.0")]
 impl<'a> DoubleEndedIterator for Drain<'a> {
     #[inline]
     fn next_back(&mut self) -> Option<char> {
         self.iter.next_back()
     }
 }