// 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 or the MIT license // , 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, Index, IndexMut}; use core::ptr; use core::slice; 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`]``, 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 thirteen 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, } /// 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, 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: /// /// ``` /// // 𝄞muic /// 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`]) 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`]: ../../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) -> Result { 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()); /// /// // 𝄞muic /// 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 { decode_utf16(v.iter().cloned()).collect::>().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: /// /// ``` /// // 𝄞music /// 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. /// /// # 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) -> 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 { 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), ch_len => { let cur_len = self.len(); // This may use up to 4 bytes. self.vec.reserve(ch_len); 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), ch_len); let used = ch.encode_utf8(slice).unwrap_or(0); self.vec.set_len(cur_len + used); } } } } /// 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. /// /// # Panics /// /// Panics if `new_len` > current length, or 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) { 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 { 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 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 len = self.len(); assert!(idx < len); let ch = self.char_at(idx); let next = idx + ch.len_utf8(); 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)); self.vec.reserve(4); let mut bits = [0; 4]; let amt = ch.encode_utf8(&mut bits).unwrap(); unsafe { ptr::copy(self.vec.as_ptr().offset(idx as isize), self.vec.as_mut_ptr().offset((idx + amt) as isize), len - idx); ptr::copy(bits.as_ptr(), self.vec.as_mut_ptr().offset(idx as isize), amt); self.vec.set_len(len + amt); } } /// 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 { &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(&mut self, range: R) -> Drain where R: RangeArgument { // 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`. /// /// 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 { let slice = self.vec.into_boxed_slice(); unsafe { mem::transmute::, Box>(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 { 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 for String { fn from_iter>(iterable: I) -> String { let mut buf = String::new(); buf.extend(iterable); buf } } #[stable(feature = "rust1", since = "1.0.0")] impl<'a> FromIterator<&'a str> for String { fn from_iter>(iterable: I) -> String { let mut buf = String::new(); buf.extend(iterable); buf } } #[stable(feature = "extend_string", since = "1.4.0")] impl FromIterator for String { fn from_iter>(iterable: I) -> String { let mut buf = String::new(); buf.extend(iterable); buf } } #[stable(feature = "rust1", since = "1.0.0")] impl Extend for String { fn extend>(&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) } } } #[stable(feature = "extend_ref", since = "1.2.0")] impl<'a> Extend<&'a char> for String { fn extend>(&mut self, iterable: I) { self.extend(iterable.into_iter().cloned()); } } #[stable(feature = "rust1", since = "1.0.0")] impl<'a> Extend<&'a str> for String { fn extend>(&mut self, iterable: I) { for s in iterable { self.push_str(s) } } } #[stable(feature = "extend_string", since = "1.4.0")] impl Extend for String { fn extend>(&mut self, iterable: I) { for s in iterable { 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(&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 = "rust1", since = "1.0.0")] impl ops::Index> for String { type Output = str; #[inline] fn index(&self, index: ops::Range) -> &str { &self[..][index] } } #[stable(feature = "rust1", since = "1.0.0")] impl ops::Index> for String { type Output = str; #[inline] fn index(&self, index: ops::RangeTo) -> &str { &self[..][index] } } #[stable(feature = "rust1", since = "1.0.0")] impl ops::Index> for String { type Output = str; #[inline] fn index(&self, index: ops::RangeFrom) -> &str { &self[..][index] } } #[stable(feature = "rust1", since = "1.0.0")] impl ops::Index 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> for String { type Output = str; #[inline] fn index(&self, index: ops::RangeInclusive) -> &str { Index::index(&**self, index) } } #[unstable(feature = "inclusive_range", reason = "recently added, follows RFC", issue = "28237")] impl ops::Index> for String { type Output = str; #[inline] fn index(&self, index: ops::RangeToInclusive) -> &str { Index::index(&**self, index) } } #[stable(feature = "derefmut_for_string", since = "1.2.0")] impl ops::IndexMut> for String { #[inline] fn index_mut(&mut self, index: ops::Range) -> &mut str { &mut self[..][index] } } #[stable(feature = "derefmut_for_string", since = "1.2.0")] impl ops::IndexMut> for String { #[inline] fn index_mut(&mut self, index: ops::RangeTo) -> &mut str { &mut self[..][index] } } #[stable(feature = "derefmut_for_string", since = "1.2.0")] impl ops::IndexMut> for String { #[inline] fn index_mut(&mut self, index: ops::RangeFrom) -> &mut str { &mut self[..][index] } } #[stable(feature = "derefmut_for_string", since = "1.2.0")] impl ops::IndexMut 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> for String { #[inline] fn index_mut(&mut self, index: ops::RangeInclusive) -> &mut str { IndexMut::index_mut(&mut **self, index) } } #[unstable(feature = "inclusive_range", reason = "recently added, follows RFC", issue = "28237")] impl ops::IndexMut> for String { #[inline] fn index_mut(&mut self, index: ops::RangeToInclusive) -> &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 { 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 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 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 for Cow<'a, str> { #[inline] fn from(s: String) -> Cow<'a, str> { Cow::Owned(s) } } #[stable(feature = "rust1", since = "1.0.0")] impl Into> for String { fn into(self) -> Vec { self.into_bytes() } } #[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 { self.iter.next() } fn size_hint(&self) -> (usize, Option) { self.iter.size_hint() } } #[stable(feature = "drain", since = "1.6.0")] impl<'a> DoubleEndedIterator for Drain<'a> { #[inline] fn next_back(&mut self) -> Option { self.iter.next_back() } }