// 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. //! //! [`ToString`]: trait.ToString.html //! //! # Examples //! //! There are multiple ways to create a new [`String`] from a string literal: //! //! ``` //! 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 //! `+`: //! //! [`String`]: struct.String.html //! //! ``` //! 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. //! //! ``` //! 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::char::{decode_utf16, REPLACEMENT_CHARACTER}; use core::fmt; use core::hash; use core::iter::{FromIterator, FusedIterator}; use core::ops::Bound::{Excluded, Included, Unbounded}; use core::ops::{self, Add, AddAssign, Index, IndexMut, RangeBounds}; use core::ptr; use core::str::pattern::Pattern; use core::str::lossy; use alloc::CollectionAllocErr; use borrow::{Cow, ToOwned}; use boxed::Box; use str::{self, from_boxed_utf8_unchecked, FromStr, Utf8Error, Chars}; use vec::Vec; /// 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!"); /// ``` /// /// [`String::from`]: #method.from /// [`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`: /// /// ```compile_fail,E0277 /// 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. Furthermore, it's not clear what sort of /// thing the index should return: a byte, a codepoint, or a grapheme cluster. /// The [`bytes`] and [`chars`] methods return iterators over the first /// two, respectively. /// /// [`bytes`]: #method.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 a /// function which takes a [`&str`] by using an ampersand (`&`): /// /// ``` /// fn takes_str(s: &str) { } /// /// let s = String::from("Hello"); /// /// takes_str(&s); /// ``` /// /// 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. /// /// In certain cases Rust doesn't have enough information to make this /// conversion, known as [`Deref`] coercion. In the following example a string /// slice [`&'a str`][`&str`] implements the trait `TraitExample`, and the function /// `example_func` takes anything that implements the trait. In this case Rust /// would need to make two implicit conversions, which Rust doesn't have the /// means to do. For that reason, the following example will not compile. /// /// ```compile_fail,E0277 /// trait TraitExample {} /// /// impl<'a> TraitExample for &'a str {} /// /// fn example_func(example_arg: A) {} /// /// fn main() { /// let example_string = String::from("example_string"); /// example_func(&example_string); /// } /// ``` /// /// There are two options that would work instead. The first would be to /// change the line `example_func(&example_string);` to /// `example_func(example_string.as_str());`, using the method [`as_str()`] /// to explicitly extract the string slice containing the string. The second /// way changes `example_func(&example_string);` to /// `example_func(&*example_string);`. In this case we are dereferencing a /// `String` to a [`str`][`&str`], then referencing the [`str`][`&str`] back to /// [`&str`]. The second way is more idiomatic, however both work to do the /// conversion explicitly rather than relying on the implicit conversion. /// /// # 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. /// /// [`&str`]: ../../std/primitive.str.html /// [`Deref`]: ../../std/ops/trait.Deref.html /// [`as_str()`]: struct.String.html#method.as_str #[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, it 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. /// /// 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. /// /// 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`]. /// /// The inverse of this method is [`as_bytes`]. /// /// # 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. /// /// [`from_utf8_unchecked`]: struct.String.html#method.from_utf8_unchecked /// [`&str`]: ../../std/primitive.str.html /// [`u8`]: ../../std/primitive.u8.html /// [`Vec`]: ../../std/vec/struct.Vec.html /// [`str::from_utf8`]: ../../std/str/fn.from_utf8.html /// [`as_bytes`]: struct.String.html#method.as_bytes /// [`FromUtf8Error`]: struct.FromUtf8Error.html /// [`Err`]: ../../stdresult/enum.Result.html#variant.Err #[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 iter = lossy::Utf8Lossy::from_bytes(v).chunks(); let (first_valid, first_broken) = if let Some(chunk) = iter.next() { let lossy::Utf8LossyChunk { valid, broken } = chunk; if valid.len() == v.len() { debug_assert!(broken.is_empty()); return Cow::Borrowed(valid); } (valid, broken) } else { return Cow::Borrowed(""); }; const REPLACEMENT: &'static str = "\u{FFFD}"; let mut res = String::with_capacity(v.len()); res.push_str(first_valid); if !first_broken.is_empty() { res.push_str(REPLACEMENT); } for lossy::Utf8LossyChunk { valid, broken } in iter { res.push_str(valid); if !broken.is_empty() { res.push_str(REPLACEMENT); } } Cow::Owned(res) } /// Decode a UTF-16 encoded vector `v` into a `String`, returning [`Err`] /// if `v` contains any invalid data. /// /// [`Err`]: ../../std/result/enum.Result.html#variant.Err /// /// # 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 slice `v` into a `String`, replacing /// invalid data with the replacement character (U+FFFD). /// /// Unlike [`from_utf8_lossy`] which returns a [`Cow<'a, str>`], /// `from_utf16_lossy` returns a `String` since the UTF-16 to UTF-8 /// conversion requires a memory allocation. /// /// [`from_utf8_lossy`]: #method.from_utf8_lossy /// [`Cow<'a, str>`]: ../borrow/enum.Cow.html /// /// # 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 data structures. /// /// 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) -> 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. /// /// # Examples /// /// Basic usage: /// /// ``` /// let s = String::from("foo"); /// /// assert_eq!("foo", s.as_str()); /// ``` #[inline] #[stable(feature = "string_as_str", since = "1.7.0")] pub fn as_str(&self) -> &str { self } /// Converts a `String` into a mutable string slice. /// /// # Examples /// /// Basic usage: /// /// ``` /// let mut s = String::from("foobar"); /// let s_mut_str = s.as_mut_str(); /// /// s_mut_str.make_ascii_uppercase(); /// /// assert_eq!("FOOBAR", s_mut_str); /// ``` #[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. /// /// # Panics /// /// Panics if the new capacity overflows [`usize`]. /// /// [`reserve_exact`]: struct.String.html#method.reserve_exact /// [`usize`]: ../../std/primitive.usize.html /// /// # 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) } /// Tries to reserve capacity for at least `additional` more elements to be inserted /// in the given `String`. The collection may reserve more space to avoid /// frequent reallocations. After calling `reserve`, capacity will be /// greater than or equal to `self.len() + additional`. Does nothing if /// capacity is already sufficient. /// /// # Errors /// /// If the capacity overflows, or the allocator reports a failure, then an error /// is returned. /// /// # Examples /// /// ``` /// #![feature(try_reserve)] /// use std::collections::CollectionAllocErr; /// /// fn process_data(data: &str) -> Result { /// let mut output = String::new(); /// /// // Pre-reserve the memory, exiting if we can't /// output.try_reserve(data.len())?; /// /// // Now we know this can't OOM in the middle of our complex work /// output.push_str(data); /// /// Ok(output) /// } /// # process_data("rust").expect("why is the test harness OOMing on 4 bytes?"); /// ``` #[unstable(feature = "try_reserve", reason = "new API", issue="48043")] pub fn try_reserve(&mut self, additional: usize) -> Result<(), CollectionAllocErr> { self.vec.try_reserve(additional) } /// Tries to reserves the minimum capacity for exactly `additional` more elements to /// be inserted in the given `String`. After calling `reserve_exact`, /// capacity will be greater than or equal to `self.len() + additional`. /// 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. /// /// # Errors /// /// If the capacity overflows, or the allocator reports a failure, then an error /// is returned. /// /// # Examples /// /// ``` /// #![feature(try_reserve)] /// use std::collections::CollectionAllocErr; /// /// fn process_data(data: &str) -> Result { /// let mut output = String::new(); /// /// // Pre-reserve the memory, exiting if we can't /// output.try_reserve(data.len())?; /// /// // Now we know this can't OOM in the middle of our complex work /// output.push_str(data); /// /// Ok(output) /// } /// # process_data("rust").expect("why is the test harness OOMing on 4 bytes?"); /// ``` #[unstable(feature = "try_reserve", reason = "new API", issue="48043")] pub fn try_reserve_exact(&mut self, additional: usize) -> Result<(), CollectionAllocErr> { self.vec.try_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() } /// Shrinks the capacity of this `String` with a lower bound. /// /// The capacity will remain at least as large as both the length /// and the supplied value. /// /// Panics if the current capacity is smaller than the supplied /// minimum capacity. /// /// # Examples /// /// ``` /// #![feature(shrink_to)] /// let mut s = String::from("foo"); /// /// s.reserve(100); /// assert!(s.capacity() >= 100); /// /// s.shrink_to(10); /// assert!(s.capacity() >= 10); /// s.shrink_to(0); /// assert!(s.capacity() >= 3); /// ``` #[inline] #[unstable(feature = "shrink_to", reason = "new API", issue="0")] pub fn shrink_to(&mut self, min_capacity: usize) { self.vec.shrink_to(min_capacity) } /// Appends the given [`char`] to the end of this `String`. /// /// [`char`]: ../../std/primitive.char.html /// /// # 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(&mut [0; 4]).as_bytes()), } } /// Returns a byte slice of this `String`'s contents. /// /// The inverse of this method is [`from_utf8`]. /// /// [`from_utf8`]: #method.from_utf8 /// /// # 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. /// /// Note that this method has no effect on the allocated capacity /// of the string /// /// # 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. /// /// [`None`]: ../../std/option/enum.Option.html#variant.None /// /// # 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 ch = self.chars().rev().next()?; 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 } /// Retains only the characters specified by the predicate. /// /// In other words, remove all characters `c` such that `f(c)` returns `false`. /// This method operates in place and preserves the order of the retained /// characters. /// /// # Examples /// /// ``` /// let mut s = String::from("f_o_ob_ar"); /// /// s.retain(|c| c != '_'); /// /// assert_eq!(s, "foobar"); /// ``` #[inline] #[stable(feature = "string_retain", since = "1.26.0")] pub fn retain(&mut self, mut f: F) where F: FnMut(char) -> bool { let len = self.len(); let mut del_bytes = 0; let mut idx = 0; while idx < len { let ch = unsafe { self.slice_unchecked(idx, len).chars().next().unwrap() }; let ch_len = ch.len_utf8(); if !f(ch) { del_bytes += ch_len; } else if del_bytes > 0 { unsafe { ptr::copy(self.vec.as_ptr().offset(idx as isize), self.vec.as_mut_ptr().offset((idx - del_bytes) as isize), ch_len); } } // Point idx to the next char idx += ch_len; } if del_bytes > 0 { unsafe { self.vec.set_len(len - del_bytes); } } } /// 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) { assert!(self.is_char_boundary(idx)); let mut bits = [0; 4]; let bits = ch.encode_utf8(&mut bits).as_bytes(); unsafe { self.insert_bytes(idx, bits); } } 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 slice 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::from("bar"); /// /// s.insert_str(0, "foo"); /// /// assert_eq!("foobar", s); /// ``` #[inline] #[stable(feature = "insert_str", since = "1.16.0")] pub fn insert_str(&mut self, idx: usize, string: &str) { 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 { &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 } /// Splits the string into two at the given index. /// /// Returns a newly allocated `String`. `self` contains bytes `[0, at)`, and /// the returned `String` contains bytes `[at, len)`. `at` must be on the /// boundary of a UTF-8 code point. /// /// Note that the capacity of `self` does not change. /// /// # Panics /// /// Panics if `at` is not on a `UTF-8` code point boundary, or if it is beyond the last /// code point of the string. /// /// # Examples /// /// ``` /// # fn main() { /// let mut hello = String::from("Hello, World!"); /// let world = hello.split_off(7); /// assert_eq!(hello, "Hello, "); /// assert_eq!(world, "World!"); /// # } /// ``` #[inline] #[stable(feature = "string_split_off", since = "1.16.0")] pub fn split_off(&mut self, at: usize) -> String { assert!(self.is_char_boundary(at)); let other = self.vec.split_off(at); unsafe { String::from_utf8_unchecked(other) } } /// 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() } /// Creates 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: RangeBounds { // 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 = match range.start() { Included(&n) => n, Excluded(&n) => n + 1, Unbounded => 0, }; let end = match range.end() { Included(&n) => n + 1, Excluded(&n) => n, Unbounded => 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, end, iter: chars_iter, string: self_ptr, } } /// Removes the specified range in the string, /// and replaces it with the given string. /// The given string doesn't need to be the same length as the range. /// /// # 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 /// [`Vec::splice`]: ../../std/vec/struct.Vec.html#method.splice /// /// # Examples /// /// Basic usage: /// /// ``` /// let mut s = String::from("α is alpha, β is beta"); /// let beta_offset = s.find('β').unwrap_or(s.len()); /// /// // Replace the range up until the β from the string /// s.replace_range(..beta_offset, "Α is capital alpha; "); /// assert_eq!(s, "Α is capital alpha; β is beta"); /// ``` #[stable(feature = "splice", since = "1.27.0")] pub fn replace_range(&mut self, range: R, replace_with: &str) where R: RangeBounds { // Memory safety // // Replace_range does not have the memory safety issues of a vector Splice. // of the vector version. The data is just plain bytes. match range.start() { Included(&n) => assert!(self.is_char_boundary(n)), Excluded(&n) => assert!(self.is_char_boundary(n + 1)), Unbounded => {}, }; match range.end() { Included(&n) => assert!(self.is_char_boundary(n + 1)), Excluded(&n) => assert!(self.is_char_boundary(n)), Unbounded => {}, }; unsafe { self.as_mut_vec() }.splice(range, replace_with.bytes()); } /// Converts this `String` into a [`Box`]`<`[`str`]`>`. /// /// This will drop any excess capacity. /// /// [`Box`]: ../../std/boxed/struct.Box.html /// [`str`]: ../../std/primitive.str.html /// /// # Examples /// /// Basic usage: /// /// ``` /// let s = String::from("hello"); /// /// let b = s.into_boxed_str(); /// ``` #[stable(feature = "box_str", since = "1.4.0")] #[inline] pub fn into_boxed_str(self) -> Box { let slice = self.vec.into_boxed_slice(); unsafe { from_boxed_utf8_unchecked(slice) } } } impl FromUtf8Error { /// Returns a slice of [`u8`]s bytes that were attempted to convert to a `String`. /// /// # Examples /// /// Basic usage: /// /// ``` /// // some invalid bytes, in a vector /// let bytes = vec![0, 159]; /// /// let value = String::from_utf8(bytes); /// /// assert_eq!(&[0, 159], value.unwrap_err().as_bytes()); /// ``` #[stable(feature = "from_utf8_error_as_bytes", since = "1.26.0")] pub fn as_bytes(&self) -> &[u8] { &self.bytes[..] } /// 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>(iter: I) -> String { let mut buf = String::new(); buf.extend(iter); buf } } #[stable(feature = "string_from_iter_by_ref", since = "1.17.0")] impl<'a> FromIterator<&'a char> for String { fn from_iter>(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>(iter: I) -> String { let mut buf = String::new(); buf.extend(iter); buf } } #[stable(feature = "extend_string", since = "1.4.0")] impl FromIterator for String { fn from_iter>(iter: I) -> String { let mut buf = String::new(); buf.extend(iter); buf } } #[stable(feature = "herd_cows", since = "1.19.0")] impl<'a> FromIterator> for String { fn from_iter>>(iter: I) -> String { let mut buf = String::new(); buf.extend(iter); buf } } #[stable(feature = "rust1", since = "1.0.0")] impl Extend for String { fn extend>(&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>(&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>(&mut self, iter: I) { for s in iter { self.push_str(s) } } } #[stable(feature = "extend_string", since = "1.4.0")] impl Extend for String { fn extend>(&mut self, iter: I) { for s in iter { self.push_str(&s) } } } #[stable(feature = "herd_cows", since = "1.19.0")] impl<'a> Extend> for String { fn extend>>(&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 { /// Creates an empty `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) } } /// Implements the `+` operator for concatenating two strings. /// /// This consumes the `String` on the left-hand side and re-uses its buffer (growing it if /// necessary). This is done to avoid allocating a new `String` and copying the entire contents on /// every operation, which would lead to `O(n^2)` running time when building an `n`-byte string by /// repeated concatenation. /// /// The string on the right-hand side is only borrowed; its contents are copied into the returned /// `String`. /// /// # Examples /// /// Concatenating two `String`s takes the first by value and borrows the second: /// /// ``` /// let a = String::from("hello"); /// let b = String::from(" world"); /// let c = a + &b; /// // `a` is moved and can no longer be used here. /// ``` /// /// If you want to keep using the first `String`, you can clone it and append to the clone instead: /// /// ``` /// let a = String::from("hello"); /// let b = String::from(" world"); /// let c = a.clone() + &b; /// // `a` is still valid here. /// ``` /// /// Concatenating `&str` slices can be done by converting the first to a `String`: /// /// ``` /// let a = "hello"; /// let b = " world"; /// let c = a.to_string() + b; /// ``` #[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 } } /// Implements the `+=` operator for appending to a `String`. /// /// This has the same behavior as the [`push_str`] method. /// /// [`push_str`]: struct.String.html#method.push_str #[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> 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) } } } #[stable(feature = "inclusive_range", since = "1.26.0")] impl ops::Index> for String { type Output = str; #[inline] fn index(&self, index: ops::RangeInclusive) -> &str { Index::index(&**self, index) } } #[stable(feature = "inclusive_range", since = "1.26.0")] 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 = "1.3.0")] 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 = "1.3.0")] 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 = "1.3.0")] 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 = "1.3.0")] impl ops::IndexMut for String { #[inline] fn index_mut(&mut self, _index: ops::RangeFull) -> &mut str { unsafe { str::from_utf8_unchecked_mut(&mut *self.vec) } } } #[stable(feature = "inclusive_range", since = "1.26.0")] impl ops::IndexMut> for String { #[inline] fn index_mut(&mut self, index: ops::RangeInclusive) -> &mut str { IndexMut::index_mut(&mut **self, index) } } #[stable(feature = "inclusive_range", since = "1.26.0")] 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 = "1.3.0")] impl ops::DerefMut for String { #[inline] fn deref_mut(&mut self) -> &mut str { unsafe { str::from_utf8_unchecked_mut(&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()); /// ``` #[rustc_conversion_suggestion] #[stable(feature = "rust1", since = "1.0.0")] fn to_string(&self) -> String; } /// # Panics /// /// In this implementation, the `to_string` method panics /// if the `Display` implementation returns an error. /// This indicates an incorrect `Display` implementation /// since `fmt::Write for String` never returns an error itself. #[stable(feature = "rust1", since = "1.0.0")] impl ToString for T { #[inline] default fn to_string(&self) -> String { use core::fmt::Write; let mut buf = String::new(); buf.write_fmt(format_args!("{}", self)) .expect("a Display implementation return an error unexpectedly"); 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 = "cow_str_to_string_specialization", since = "1.17.0")] impl<'a> ToString for Cow<'a, str> { #[inline] fn to_string(&self) -> String { self[..].to_owned() } } #[stable(feature = "string_to_string_specialization", since = "1.17.0")] impl ToString for String { #[inline] fn to_string(&self) -> String { self.to_owned() } } #[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() } } // note: test pulls in libstd, which causes errors here #[cfg(not(test))] #[stable(feature = "string_from_box", since = "1.18.0")] impl From> for String { fn from(s: Box) -> String { s.into_string() } } #[stable(feature = "box_from_str", since = "1.20.0")] impl From for Box { fn from(s: String) -> Box { s.into_boxed_str() } } #[stable(feature = "string_from_cow_str", since = "1.14.0")] impl<'a> From> for String { fn from(s: Cow<'a, str>) -> String { s.into_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 = "cow_str_from_iter", since = "1.12.0")] impl<'a> FromIterator for Cow<'a, str> { fn from_iter>(it: I) -> Cow<'a, str> { Cow::Owned(FromIterator::from_iter(it)) } } #[stable(feature = "cow_str_from_iter", since = "1.12.0")] impl<'a, 'b> FromIterator<&'b str> for Cow<'a, str> { fn from_iter>(it: I) -> Cow<'a, str> { Cow::Owned(FromIterator::from_iter(it)) } } #[stable(feature = "cow_str_from_iter", since = "1.12.0")] impl<'a> FromIterator for Cow<'a, str> { fn from_iter>(it: I) -> Cow<'a, str> { Cow::Owned(FromIterator::from_iter(it)) } } #[stable(feature = "from_string_for_vec_u8", since = "1.14.0")] impl From for Vec { fn from(string: String) -> Vec { string.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 = "collection_debug", since = "1.17.0")] impl<'a> fmt::Debug for Drain<'a> { fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { f.pad("Drain { .. }") } } #[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() } } #[stable(feature = "fused", since = "1.26.0")] impl<'a> FusedIterator for Drain<'a> {}