Struct alloc::string::String

pub struct String { /* fields omitted */ }

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.

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!");

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);

UTF-8

Strings 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:

let s = "hello";

println!("The first letter of s is {}", s[0]); // ERROR!!!

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.

Deref

Strings implement Deref<Target=str>, 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 &strs 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 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.

trait TraitExample {}

impl<'a> TraitExample for &'a str {}

fn example_func<A: TraitExample>(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, then referencing the 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);

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:

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());
}

We end up with a different output:

25
25
25
25
25
25

Here, there's no need to allocate more memory inside the loop.

Methods

impl String

pub fn new() -> 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.

Examples

Basic usage:

let s = String::new();

pub fn with_capacity(capacity: usize) -> String

Creates a new empty String with a particular capacity.

Strings 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.

If the given capacity is 0, no allocation will occur, and this method is identical to the new method.

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');

pub fn from_utf8(vec: Vec<u8>) -> Result<String, FromUtf8Error>

Converts a vector of bytes to a String.

A string slice (&str) is made of bytes (u8), and a vector of bytes (Vec<u8>) is made of bytes, so this function converts between the two. Not all byte slices are valid Strings, 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.

pub fn from_utf8_lossy<'a>(v: &'a [u8]) -> Cow<'a, str>

Converts a slice of bytes to a string, including invalid characters.

Strings are made of bytes (u8), and a slice of bytes (&[u8]) 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: �

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.

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.

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);

pub fn from_utf16(v: &[u16]) -> Result<String, FromUtf16Error>

Decode a UTF-16 encoded vector v into a String, returning Err if v contains any invalid data.

Examples

Basic usage:

// 𝄞music
let v = &[0xD834, 0xDD1E, 0x006d, 0x0075,
          0x0073, 0x0069, 0x0063];
assert_eq!(String::from("𝄞music"),
           String::from_utf16(v).unwrap());

// 𝄞mu<invalid>ic
let v = &[0xD834, 0xDD1E, 0x006d, 0x0075,
          0xD800, 0x0069, 0x0063];
assert!(String::from_utf16(v).is_err());

pub fn from_utf16_lossy(v: &[u16]) -> String

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.

Examples

Basic usage:

// 𝄞mus<invalid>ic<invalid>
let v = &[0xD834, 0xDD1E, 0x006d, 0x0075,
          0x0073, 0xDD1E, 0x0069, 0x0063,
          0xD834];

assert_eq!(String::from("𝄞mus\u{FFFD}ic\u{FFFD}"),
           String::from_utf16_lossy(v));

pub unsafe fn from_raw_parts(
    buf: *mut u8,
    length: usize,
    capacity: usize
) -> String

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);
}

pub unsafe fn from_utf8_unchecked(bytes: Vec<u8>) -> String

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.

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 Strings 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);

pub fn into_bytes(self) -> Vec<u8>

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[..]);

pub fn as_str(&self) -> &str

Extracts a string slice containing the entire string.

Examples

Basic usage:

let s = String::from("foo");

assert_eq!("foo", s.as_str());

pub fn as_mut_str(&mut self) -> &mut str

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);

pub fn push_str(&mut self, string: &str)

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);

pub fn capacity(&self) -> usize

Returns this String's capacity, in bytes.

Examples

Basic usage:

let s = String::with_capacity(10);

assert!(s.capacity() >= 10);

pub fn reserve(&mut self, additional: usize)

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.

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());

pub fn reserve_exact(&mut self, additional: usize)

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.

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());

pub fn shrink_to_fit(&mut self)

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());

pub fn push(&mut self, ch: char)

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);

pub fn as_bytes(&self) -> &[u8]

Returns a byte slice of this String's contents.

The inverse of this method is from_utf8.

Examples

Basic usage:

let s = String::from("hello");

assert_eq!(&[104, 101, 108, 108, 111], s.as_bytes());

pub fn truncate(&mut self, new_len: usize)

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.

Examples

Basic usage:

let mut s = String::from("hello");

s.truncate(2);

assert_eq!("he", s);

pub fn pop(&mut self) -> Option<char>

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);

pub fn remove(&mut self, idx: usize) -> char

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.

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');

pub fn retain<F>(&mut self, f: F) where
    F: FnMut(char) -> bool, 

🔬 This is a nightly-only experimental API. (string_retain #43874)

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

#![feature(string_retain)]

let mut s = String::from("f_o_ob_ar");

s.retain(|c| c != '_');

assert_eq!(s, "foobar");

pub fn insert(&mut self, idx: usize, ch: char)

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.

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);

pub fn insert_str(&mut self, idx: usize, string: &str)

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.

Examples

Basic usage:

let mut s = String::from("bar");

s.insert_str(0, "foo");

assert_eq!("foobar", s);

pub unsafe fn as_mut_vec(&mut self) -> &mut Vec<u8>

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 Strings 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");

pub fn len(&self) -> usize

Returns the length of this String, in bytes.

Examples

Basic usage:

let a = String::from("foo");

assert_eq!(a.len(), 3);

pub fn is_empty(&self) -> bool

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());

pub fn split_off(&mut self, at: usize) -> String

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

let mut hello = String::from("Hello, World!");
let world = hello.split_off(7);
assert_eq!(hello, "Hello, ");
assert_eq!(world, "World!");

pub fn clear(&mut self)

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());

Important traits for Drain<'a>

impl<'a> Iterator for Drain<'a> type Item = char;

pub fn drain<R>(&mut self, range: R) -> Drain where
    R: RangeArgument<usize>, 

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.

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, "");

pub fn splice<R>(&mut self, range: R, replace_with: &str) where
    R: RangeArgument<usize>, 

🔬 This is a nightly-only experimental API. (splice #44643)

recently added

Creates a splicing iterator that 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.

Note: Unlike Vec::splice, the replacement happens eagerly, and this method does not return the removed chars.

Panics

Panics if the starting point or end point do not lie on a char boundary, or if they're out of bounds.

Examples

Basic usage:

#![feature(splice)]
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.splice(..beta_offset, "Α is capital alpha; ");
assert_eq!(s, "Α is capital alpha; β is beta");

Important traits for Box<I>

impl<I: Iterator + ?Sized> Iterator for Box<I> type Item = I::Item;

pub fn into_boxed_str(self) -> Box<str>

Converts this String into a Box<str>.

This will drop any excess capacity.

Examples

Basic usage:

let s = String::from("hello");

let b = s.into_boxed_str();

Trait Implementations

impl From<String> for Arc<str>

fn from(v: String) -> Arc<str>

Performs the conversion.

impl From<String> for Rc<str>

fn from(v: String) -> Rc<str>

Performs the conversion.

impl Borrow<str> for String

fn borrow(&self) -> &str

Immutably borrows from an owned value.

impl PartialOrd for String

fn partial_cmp(&self, __arg_0: &String) -> Option<Ordering>

This method returns an ordering between self and other values if one exists.

fn lt(&self, __arg_0: &String) -> bool

This method tests less than (for self and other) and is used by the < operator.

fn le(&self, __arg_0: &String) -> bool

This method tests less than or equal to (for self and other) and is used by the <= operator.

fn gt(&self, __arg_0: &String) -> bool

This method tests greater than (for self and other) and is used by the > operator.

fn ge(&self, __arg_0: &String) -> bool

This method tests greater than or equal to (for self and other) and is used by the >= operator.

impl Eq for String

impl Ord for String

fn cmp(&self, __arg_0: &String) -> Ordering

This method returns an Ordering between self and other.

fn max(self, other: Self) -> Self

Compares and returns the maximum of two values.

fn min(self, other: Self) -> Self

Compares and returns the minimum of two values.

impl Clone for String

fn clone(&self) -> Self

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl FromIterator<char> for String

fn from_iter<I: IntoIterator<Item = char>>(iter: I) -> String

Creates a value from an iterator.

impl<'a> FromIterator<&'a char> for String

fn from_iter<I: IntoIterator<Item = &'a char>>(iter: I) -> String

Creates a value from an iterator.

impl<'a> FromIterator<&'a str> for String

fn from_iter<I: IntoIterator<Item = &'a str>>(iter: I) -> String

Creates a value from an iterator.

impl FromIterator<String> for String

fn from_iter<I: IntoIterator<Item = String>>(iter: I) -> String

Creates a value from an iterator.

impl<'a> FromIterator<Cow<'a, str>> for String

fn from_iter<I: IntoIterator<Item = Cow<'a, str>>>(iter: I) -> String

Creates a value from an iterator.

impl Extend<char> for String

fn extend<I: IntoIterator<Item = char>>(&mut self, iter: I)

Extends a collection with the contents of an iterator.

impl<'a> Extend<&'a char> for String

fn extend<I: IntoIterator<Item = &'a char>>(&mut self, iter: I)

Extends a collection with the contents of an iterator.

impl<'a> Extend<&'a str> for String

fn extend<I: IntoIterator<Item = &'a str>>(&mut self, iter: I)

Extends a collection with the contents of an iterator.

impl Extend<String> for String

fn extend<I: IntoIterator<Item = String>>(&mut self, iter: I)

Extends a collection with the contents of an iterator.

impl<'a> Extend<Cow<'a, str>> for String

fn extend<I: IntoIterator<Item = Cow<'a, str>>>(&mut self, iter: I)

Extends a collection with the contents of an iterator.

impl<'a, 'b> Pattern<'a> for &'b String

A convenience impl that delegates to the impl for &str

type Searcher = <&'b str as Pattern<'a>>::Searcher

🔬 This is a nightly-only experimental API. (pattern #27721)

API not fully fleshed out and ready to be stabilized

Associated searcher for this pattern

fn into_searcher(self, haystack: &'a str) -> <&'b str as Pattern<'a>>::Searcher

🔬 This is a nightly-only experimental API. (pattern #27721)

API not fully fleshed out and ready to be stabilized

Constructs the associated searcher from self and the haystack to search in.

fn is_contained_in(self, haystack: &'a str) -> bool

🔬 This is a nightly-only experimental API. (pattern #27721)

API not fully fleshed out and ready to be stabilized

Checks whether the pattern matches anywhere in the haystack

fn is_prefix_of(self, haystack: &'a str) -> bool

🔬 This is a nightly-only experimental API. (pattern #27721)

API not fully fleshed out and ready to be stabilized

Checks whether the pattern matches at the front of the haystack

fn is_suffix_of(self, haystack: &'a str) -> bool where
    Self::Searcher: ReverseSearcher<'a>, 

🔬 This is a nightly-only experimental API. (pattern #27721)

API not fully fleshed out and ready to be stabilized

Checks whether the pattern matches at the back of the haystack

impl PartialEq for String

fn eq(&self, other: &String) -> bool

This method tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &String) -> bool

This method tests for !=.

impl<'a, 'b> PartialEq<str> for String

fn eq(&self, other: &str) -> bool

This method tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &str) -> bool

This method tests for !=.

impl<'a, 'b> PartialEq<String> for str

fn eq(&self, other: &String) -> bool

This method tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &String) -> bool

This method tests for !=.

impl<'a, 'b> PartialEq<&'a str> for String

fn eq(&self, other: &&'a str) -> bool

This method tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &&'a str) -> bool

This method tests for !=.

impl<'a, 'b> PartialEq<String> for &'a str

fn eq(&self, other: &String) -> bool

This method tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &String) -> bool

This method tests for !=.

impl<'a, 'b> PartialEq<String> for Cow<'a, str>

fn eq(&self, other: &String) -> bool

This method tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &String) -> bool

This method tests for !=.

impl<'a, 'b> PartialEq<Cow<'a, str>> for String

fn eq(&self, other: &Cow<'a, str>) -> bool

This method tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Cow<'a, str>) -> bool

This method tests for !=.

impl Default for String

fn default() -> String

Creates an empty String.

impl Display for String

fn fmt(&self, f: &mut Formatter) -> Result

Formats the value using the given formatter.

impl Debug for String

fn fmt(&self, f: &mut Formatter) -> Result

Formats the value using the given formatter.

impl Hash for String

fn hash<H: Hasher>(&self, hasher: &mut H)

Feeds this value into the given [Hasher].

fn hash_slice<H>(data: &[Self], state: &mut H) where
    H: Hasher, 

Feeds a slice of this type into the given [Hasher].

impl<'a> Add<&'a str> for String

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 Strings 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;

type Output = String

The resulting type after applying the + operator.

fn add(self, other: &str) -> String

Performs the + operation.

impl<'a> AddAssign<&'a str> for String

Implements the += operator for appending to a String.

This has the same behavior as the push_str method.

fn add_assign(&mut self, other: &str)

Performs the += operation.

impl Index<Range<usize>> for String

type Output = str

The returned type after indexing.

fn index(&self, index: Range<usize>) -> &str

Performs the indexing (container[index]) operation.

impl Index<RangeTo<usize>> for String

type Output = str

The returned type after indexing.

fn index(&self, index: RangeTo<usize>) -> &str

Performs the indexing (container[index]) operation.

impl Index<RangeFrom<usize>> for String

type Output = str

The returned type after indexing.

fn index(&self, index: RangeFrom<usize>) -> &str

Performs the indexing (container[index]) operation.

impl Index<RangeFull> for String

type Output = str

The returned type after indexing.

fn index(&self, _index: RangeFull) -> &str

Performs the indexing (container[index]) operation.

impl Index<RangeInclusive<usize>> for String

type Output = str

The returned type after indexing.

fn index(&self, index: RangeInclusive<usize>) -> &str

Performs the indexing (container[index]) operation.

impl Index<RangeToInclusive<usize>> for String

type Output = str

The returned type after indexing.

fn index(&self, index: RangeToInclusive<usize>) -> &str

Performs the indexing (container[index]) operation.

impl IndexMut<Range<usize>> for String

fn index_mut(&mut self, index: Range<usize>) -> &mut str

Performs the mutable indexing (container[index]) operation.

impl IndexMut<RangeTo<usize>> for String

fn index_mut(&mut self, index: RangeTo<usize>) -> &mut str

Performs the mutable indexing (container[index]) operation.

impl IndexMut<RangeFrom<usize>> for String

fn index_mut(&mut self, index: RangeFrom<usize>) -> &mut str

Performs the mutable indexing (container[index]) operation.

impl IndexMut<RangeFull> for String

fn index_mut(&mut self, _index: RangeFull) -> &mut str

Performs the mutable indexing (container[index]) operation.

impl IndexMut<RangeInclusive<usize>> for String

fn index_mut(&mut self, index: RangeInclusive<usize>) -> &mut str

Performs the mutable indexing (container[index]) operation.

impl IndexMut<RangeToInclusive<usize>> for String

fn index_mut(&mut self, index: RangeToInclusive<usize>) -> &mut str

Performs the mutable indexing (container[index]) operation.

impl Deref for String

type Target = str

The resulting type after dereferencing.

fn deref(&self) -> &str

Dereferences the value.

impl DerefMut for String

fn deref_mut(&mut self) -> &mut str

Mutably dereferences the value.

impl FromStr for String

type Err = ParseError

The associated error which can be returned from parsing.

fn from_str(s: &str) -> Result<String, ParseError>

Parses a string s to return a value of this type.

impl ToString for String

fn to_string(&self) -> String

Converts the given value to a String.

impl AsRef<str> for String

fn as_ref(&self) -> &str

Performs the conversion.

impl AsRef<[u8]> for String

fn as_ref(&self) -> &[u8]

Performs the conversion.

impl<'a> From<&'a str> for String

fn from(s: &'a str) -> String

Performs the conversion.

impl From<Box<str>> for String

fn from(s: Box<str>) -> String

Performs the conversion.

impl From<String> for Box<str>

Important traits for Box<I>

impl<I: Iterator + ?Sized> Iterator for Box<I> type Item = I::Item;

fn from(s: String) -> Box<str>

Performs the conversion.

impl<'a> From<Cow<'a, str>> for String

fn from(s: Cow<'a, str>) -> String

Performs the conversion.

impl<'a> From<String> for Cow<'a, str>

fn from(s: String) -> Cow<'a, str>

Performs the conversion.

impl<'a> FromIterator<String> for Cow<'a, str>

fn from_iter<I: IntoIterator<Item = String>>(it: I) -> Cow<'a, str>

Creates a value from an iterator.

impl From<String> for Vec<u8>

fn from(string: String) -> Vec<u8>

Performs the conversion.

impl Write for String

fn write_str(&mut self, s: &str) -> Result

Writes a slice of bytes into this writer, returning whether the write succeeded.

fn write_char(&mut self, c: char) -> Result

Writes a [char] into this writer, returning whether the write succeeded.

fn write_fmt(&mut self, args: Arguments) -> Result<(), Error>

Glue for usage of the [write!] macro with implementors of this trait.