string.rs

// 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.
//
// ignore-lexer-test FIXME #15679

//! An owned, growable string that enforces that its contents are valid UTF-8.

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

use core::prelude::*;

use core::default::Default;
use core::error::Error;
use core::fmt;
use core::hash;
use core::iter::{IntoIterator, FromIterator};
use core::mem;
use core::ops::{self, Deref, Add, Index};
use core::ptr;
use core::slice;
use unicode::str as unicode_str;
use unicode::str::Utf16Item;

use borrow::{Cow, IntoCow};
use str::{self, FromStr, Utf8Error};
use vec::{DerefVec, Vec, as_vec};

/// A growable string stored as a UTF-8 encoded buffer.
#[derive(Clone, PartialOrd, Eq, Ord)]
#[stable(feature = "rust1", since = "1.0.0")]
pub struct String {
    vec: Vec<u8>,
}

/// A possible error value from the `String::from_utf8` function.
#[stable(feature = "rust1", since = "1.0.0")]
#[derive(Debug)]
pub struct FromUtf8Error {
    bytes: Vec<u8>,
    error: Utf8Error,
}

/// A possible error value from the `String::from_utf16` function.
#[stable(feature = "rust1", since = "1.0.0")]
#[derive(Debug)]
pub struct FromUtf16Error(());

impl String {
    /// Creates a new string buffer initialized with the empty string.
    ///
    /// # Examples
    ///
    /// ```
    /// let mut s = String::new();
    /// ```
    #[inline]
    #[stable(feature = "rust1", since = "1.0.0")]
    pub fn new() -> String {
        String {
            vec: Vec::new(),
        }
    }

    /// Creates a new string buffer with the given capacity.
    /// The string will be able to hold exactly `capacity` bytes without
    /// reallocating. If `capacity` is 0, the string will not allocate.
    ///
    /// # Examples
    ///
    /// ```
    /// let mut s = String::with_capacity(10);
    /// ```
    #[inline]
    #[stable(feature = "rust1", since = "1.0.0")]
    pub fn with_capacity(capacity: usize) -> String {
        String {
            vec: Vec::with_capacity(capacity),
        }
    }

    /// Creates a new string buffer from the given string.
    ///
    /// # Examples
    ///
    /// ```
    /// let s = String::from_str("hello");
    /// assert_eq!(s.as_slice(), "hello");
    /// ```
    #[inline]
    #[unstable(feature = "collections",
               reason = "needs investigation to see if to_string() can match perf")]
    #[cfg(not(test))]
    pub fn from_str(string: &str) -> String {
        String { vec: <[_]>::to_vec(string.as_bytes()) }
    }

    // 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)");
    }

    /// Returns the vector as a string buffer, if possible, taking care not to
    /// copy it.
    ///
    /// # Failure
    ///
    /// If the given vector is not valid UTF-8, then the original vector and the
    /// corresponding error is returned.
    ///
    /// # Examples
    ///
    /// ```
    /// use std::str::Utf8Error;
    ///
    /// let hello_vec = vec![104, 101, 108, 108, 111];
    /// let s = String::from_utf8(hello_vec).unwrap();
    /// assert_eq!(s, "hello");
    ///
    /// let invalid_vec = vec![240, 144, 128];
    /// let s = String::from_utf8(invalid_vec).err().unwrap();
    /// assert_eq!(s.utf8_error(), Utf8Error::TooShort);
    /// assert_eq!(s.into_bytes(), [240, 144, 128]);
    /// ```
    #[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 vector of bytes to a new UTF-8 string.
    /// Any invalid UTF-8 sequences are replaced with U+FFFD REPLACEMENT CHARACTER.
    ///
    /// # Examples
    ///
    /// ```
    /// let input = b"Hello \xF0\x90\x80World";
    /// let output = String::from_utf8_lossy(input);
    /// assert_eq!(output, "Hello \u{FFFD}World");
    /// ```
    #[stable(feature = "rust1", since = "1.0.0")]
    pub fn from_utf8_lossy<'a>(v: &'a [u8]) -> Cow<'a, str> {
        let mut i = 0;
        match str::from_utf8(v) {
            Ok(s) => return Cow::Borrowed(s),
            Err(e) => {
                if let Utf8Error::InvalidByte(firstbad) = e {
                    i = firstbad;
                }
            }
        }

        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().push_all(&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().push_all(&v[subseqidx..i_]);
                    }
                    subseqidx = i;
                    res.as_mut_vec().push_all(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().push_all(&v[subseqidx..total])
            };
        }
        Cow::Owned(res)
    }

    /// Decode a UTF-16 encoded vector `v` into a `String`, returning `None`
    /// if `v` contains any invalid data.
    ///
    /// # Examples
    ///
    /// ```
    /// // 𝄞music
    /// let mut v = &mut [0xD834, 0xDD1E, 0x006d, 0x0075,
    ///                   0x0073, 0x0069, 0x0063];
    /// assert_eq!(String::from_utf16(v).unwrap(),
    ///            "𝄞music".to_string());
    ///
    /// // 𝄞mu<invalid>ic
    /// v[4] = 0xD800;
    /// assert!(String::from_utf16(v).is_err());
    /// ```
    #[stable(feature = "rust1", since = "1.0.0")]
    pub fn from_utf16(v: &[u16]) -> Result<String, FromUtf16Error> {
        let mut s = String::with_capacity(v.len());
        for c in unicode_str::utf16_items(v) {
            match c {
                Utf16Item::ScalarValue(c) => s.push(c),
                Utf16Item::LoneSurrogate(_) => return Err(FromUtf16Error(())),
            }
        }
        Ok(s)
    }

    /// Decode a UTF-16 encoded vector `v` into a string, replacing
    /// invalid data with the replacement character (U+FFFD).
    ///
    /// # Examples
    ///
    /// ```
    /// // 𝄞mus<invalid>ic<invalid>
    /// let v = &[0xD834, 0xDD1E, 0x006d, 0x0075,
    ///           0x0073, 0xDD1E, 0x0069, 0x0063,
    ///           0xD834];
    ///
    /// assert_eq!(String::from_utf16_lossy(v),
    ///            "𝄞mus\u{FFFD}ic\u{FFFD}".to_string());
    /// ```
    #[inline]
    #[stable(feature = "rust1", since = "1.0.0")]
    pub fn from_utf16_lossy(v: &[u16]) -> String {
        unicode_str::utf16_items(v).map(|c| c.to_char_lossy()).collect()
    }

    /// Creates a new `String` from a length, capacity, and pointer.
    ///
    /// This is unsafe because:
    ///
    /// * We call `Vec::from_raw_parts` to get a `Vec<u8>`;
    /// * We assume that the `Vec` contains valid UTF-8.
    #[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 new `String` without checking if
    /// it contains valid UTF-8. This is unsafe because it assumes that
    /// the UTF-8-ness of the vector has already been validated.
    #[inline]
    #[stable(feature = "rust1", since = "1.0.0")]
    pub unsafe fn from_utf8_unchecked(bytes: Vec<u8>) -> String {
        String { vec: bytes }
    }

    /// Return the underlying byte buffer, encoded as UTF-8.
    ///
    /// # Examples
    ///
    /// ```
    /// let s = String::from_str("hello");
    /// let bytes = s.into_bytes();
    /// assert_eq!(bytes, [104, 101, 108, 108, 111]);
    /// ```
    #[inline]
    #[stable(feature = "rust1", since = "1.0.0")]
    pub fn into_bytes(self) -> Vec<u8> {
        self.vec
    }

    /// Pushes the given string onto this string buffer.
    ///
    /// # Examples
    ///
    /// ```
    /// let mut s = String::from_str("foo");
    /// s.push_str("bar");
    /// assert_eq!(s, "foobar");
    /// ```
    #[inline]
    #[stable(feature = "rust1", since = "1.0.0")]
    pub fn push_str(&mut self, string: &str) {
        self.vec.push_all(string.as_bytes())
    }

    /// Returns the number of bytes that this string buffer can hold without
    /// reallocating.
    ///
    /// # Examples
    ///
    /// ```
    /// 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()
    }

    /// Reserves capacity for at least `additional` more bytes to be inserted
    /// in the given `String`. The collection may reserve more space to avoid
    /// frequent reallocations.
    ///
    /// # Panics
    ///
    /// Panics if the new capacity overflows `usize`.
    ///
    /// # Examples
    ///
    /// ```
    /// let mut s = String::new();
    /// s.reserve(10);
    /// assert!(s.capacity() >= 10);
    /// ```
    #[inline]
    #[stable(feature = "rust1", since = "1.0.0")]
    pub fn reserve(&mut self, additional: usize) {
        self.vec.reserve(additional)
    }

    /// Reserves the minimum capacity for exactly `additional` more bytes to be
    /// inserted in the given `String`. Does nothing if the capacity is already
    /// sufficient.
    ///
    /// Note that the allocator may give the collection more space than it
    /// requests. Therefore capacity can not be relied upon to be precisely
    /// minimal. Prefer `reserve` if future insertions are expected.
    ///
    /// # Panics
    ///
    /// Panics if the new capacity overflows `usize`.
    ///
    /// # Examples
    ///
    /// ```
    /// let mut s = String::new();
    /// s.reserve(10);
    /// assert!(s.capacity() >= 10);
    /// ```
    #[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 buffer to match its length.
    ///
    /// # Examples
    ///
    /// ```
    /// let mut s = String::from_str("foo");
    /// s.reserve(100);
    /// assert!(s.capacity() >= 100);
    /// s.shrink_to_fit();
    /// assert_eq!(s.capacity(), 3);
    /// ```
    #[inline]
    #[stable(feature = "rust1", since = "1.0.0")]
    pub fn shrink_to_fit(&mut self) {
        self.vec.shrink_to_fit()
    }

    /// Adds the given character to the end of the string.
    ///
    /// # Examples
    ///
    /// ```
    /// let mut s = String::from_str("abc");
    /// s.push('1');
    /// s.push('2');
    /// s.push('3');
    /// assert_eq!(s, "abc123");
    /// ```
    #[inline]
    #[stable(feature = "rust1", since = "1.0.0")]
    pub fn push(&mut self, ch: char) {
        if (ch as u32) < 0x80 {
            self.vec.push(ch as u8);
            return;
        }

        let cur_len = self.len();
        // This may use up to 4 bytes.
        self.vec.reserve(4);

        unsafe {
            // Attempt to not use an intermediate buffer by just pushing bytes
            // directly onto this string.
            let slice = slice::from_raw_parts_mut (
                self.vec.as_mut_ptr().offset(cur_len as isize),
                4
            );
            let used = ch.encode_utf8(slice).unwrap_or(0);
            self.vec.set_len(cur_len + used);
        }
    }

    /// Works with the underlying buffer as a byte slice.
    ///
    /// # Examples
    ///
    /// ```
    /// let s = String::from_str("hello");
    /// let b: &[_] = &[104, 101, 108, 108, 111];
    /// assert_eq!(s.as_bytes(), b);
    /// ```
    #[inline]
    #[stable(feature = "rust1", since = "1.0.0")]
    pub fn as_bytes(&self) -> &[u8] {
        &self.vec
    }

    /// Shortens a string to the specified length.
    ///
    /// # Panics
    ///
    /// Panics if `new_len` > current length,
    /// or if `new_len` is not a character boundary.
    ///
    /// # Examples
    ///
    /// ```
    /// let mut s = String::from_str("hello");
    /// s.truncate(2);
    /// assert_eq!(s, "he");
    /// ```
    #[inline]
    #[stable(feature = "rust1", since = "1.0.0")]
    pub fn truncate(&mut self, new_len: usize) {
        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 buffer is empty.
    ///
    /// # Examples
    ///
    /// ```
    /// let mut s = String::from_str("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 len = self.len();
        if len == 0 {
            return None
        }

        let ch = self.char_at_reverse(len);
        unsafe {
            self.vec.set_len(len - ch.len_utf8());
        }
        Some(ch)
    }

    /// Removes the character from the string buffer at byte position `idx` and
    /// returns it.
    ///
    /// # Warning
    ///
    /// This is an O(n) operation as it requires copying every element in the
    /// buffer.
    ///
    /// # Panics
    ///
    /// If `idx` does not lie on a character boundary, or if it is out of
    /// bounds, then this function will panic.
    ///
    /// # Examples
    ///
    /// ```
    /// let mut s = String::from_str("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 len = self.len();
        assert!(idx <= len);

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

    /// Insert a character into the string buffer at byte position `idx`.
    ///
    /// # Warning
    ///
    /// This is an O(n) operation as it requires copying every element in the
    /// buffer.
    ///
    /// # Panics
    ///
    /// If `idx` does not lie on a character boundary or is out of bounds, then
    /// this function will panic.
    #[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));
        self.vec.reserve(4);
        let mut bits = [0; 4];
        let amt = ch.encode_utf8(&mut bits).unwrap();

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

    /// Views the string buffer as a mutable sequence of bytes.
    ///
    /// This is unsafe because it does not check
    /// to ensure that the resulting string will be valid UTF-8.
    ///
    /// # Examples
    ///
    /// ```
    /// let mut s = String::from_str("hello");
    /// unsafe {
    ///     let vec = s.as_mut_vec();
    ///     assert!(vec == &[104, 101, 108, 108, 111]);
    ///     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
    }

    /// Return the number of bytes in this string.
    ///
    /// # Examples
    ///
    /// ```
    /// let a = "foo".to_string();
    /// assert_eq!(a.len(), 3);
    /// ```
    #[inline]
    #[stable(feature = "rust1", since = "1.0.0")]
    pub fn len(&self) -> usize { self.vec.len() }

    /// Returns true if the string contains no bytes
    ///
    /// # Examples
    ///
    /// ```
    /// 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 the string, returning it to 0 length.
    ///
    /// # Examples
    ///
    /// ```
    /// let mut s = "foo".to_string();
    /// s.clear();
    /// assert!(s.is_empty());
    /// ```
    #[inline]
    #[stable(feature = "rust1", since = "1.0.0")]
    pub fn clear(&mut self) {
        self.vec.clear()
    }
}

impl FromUtf8Error {
    /// Consume this error, returning the bytes that were attempted to make a
    /// `String` with.
    #[stable(feature = "rust1", since = "1.0.0")]
    pub fn into_bytes(self) -> Vec<u8> { self.bytes }

    /// Access the underlying UTF8-error that was the cause of this error.
    #[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 Error for FromUtf8Error {
    fn description(&self) -> &str { "invalid utf-8" }
}

#[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 Error for FromUtf16Error {
    fn description(&self) -> &str { "invalid utf-16" }
}

#[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
    }
}

#[unstable(feature = "collections",
           reason = "waiting on Extend stabilization")]
impl Extend<char> for String {
    fn extend<I: IntoIterator<Item=char>>(&mut self, iterable: I) {
        let iterator = iterable.into_iter();
        let (lower_bound, _) = iterator.size_hint();
        self.reserve(lower_bound);
        for ch in iterator {
            self.push(ch)
        }
    }
}

#[unstable(feature = "collections",
           reason = "waiting on Extend stabilization")]
impl<'a> Extend<&'a str> for String {
    fn extend<I: IntoIterator<Item=&'a str>>(&mut self, iterable: I) {
        let iterator = iterable.into_iter();
        // A guess that at least one byte per iterator element will be needed.
        let (lower_bound, _) = iterator.size_hint();
        self.reserve(lower_bound);
        for s in iterator {
            self.push_str(s)
        }
    }
}

#[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, $rhs: ty) => {
        #[stable(feature = "rust1", since = "1.0.0")]
        impl<'a> PartialEq<$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> 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, &'a str }
impl_eq! { Cow<'a, str>, String }

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

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

#[unstable(feature = "collections", reason = "waiting on Str stabilization")]
#[allow(deprecated)]
impl Str for String {
    #[inline]
    #[stable(feature = "rust1", since = "1.0.0")]
    fn as_slice(&self) -> &str {
        unsafe { mem::transmute(&*self.vec) }
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl Default for String {
    #[inline]
    #[stable(feature = "rust1", since = "1.0.0")]
    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)
    }
}

#[unstable(feature = "collections",
           reason = "recent addition, needs more experience")]
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 = "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 { mem::transmute(&*self.vec) }
    }
}

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

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

/// Wrapper type providing a `&String` reference via `Deref`.
#[unstable(feature = "collections")]
pub struct DerefString<'a> {
    x: DerefVec<'a, u8>
}

impl<'a> Deref for DerefString<'a> {
    type Target = String;

    #[inline]
    fn deref<'b>(&'b self) -> &'b String {
        unsafe { mem::transmute(&*self.x) }
    }
}

/// Convert a string slice to a wrapper type providing a `&String` reference.
///
/// # Examples
///
/// ```
/// use std::string::as_string;
///
/// fn string_consumer(s: String) {
///     assert_eq!(s, "foo".to_string());
/// }
///
/// let string = as_string("foo").clone();
/// string_consumer(string);
/// ```
#[unstable(feature = "collections")]
pub fn as_string<'a>(x: &'a str) -> DerefString<'a> {
    DerefString { x: as_vec(x.as_bytes()) }
}

#[unstable(feature = "collections", reason = "associated error type may change")]
impl FromStr for String {
    type Err = ();
    #[inline]
    fn from_str(s: &str) -> Result<String, ()> {
        Ok(String::from_str(s))
    }
}

/// A generic trait for converting a value to a string
#[stable(feature = "rust1", since = "1.0.0")]
pub trait ToString {
    /// Converts the value of `self` to an owned 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]
    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 = "rust1", since = "1.0.0")]
impl AsRef<str> for String {
    fn as_ref(&self) -> &str {
        self
    }
}

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

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

#[stable(feature = "rust1", since = "1.0.0")]
impl IntoCow<'static, str> for String {
    #[inline]
    fn into_cow(self) -> Cow<'static, str> {
        Cow::Owned(self)
    }
}

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

#[allow(deprecated)]
impl<'a> Str for Cow<'a, str> {
    #[inline]
    fn as_slice<'b>(&'b self) -> &'b str {
        &**self
    }
}

/// A clone-on-write string
#[deprecated(since = "1.0.0", reason = "use Cow<'a, str> instead")]
#[stable(feature = "rust1", since = "1.0.0")]
pub type CowString<'a> = Cow<'a, str>;

#[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(())
    }
}