Struct alloc_wg::string::String

pub struct String<A: AllocRef = Global> { /* 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:

use alloc_wg::string::String;

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:

use alloc_wg::string::String;

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:

use alloc_wg::{string::String, vec};

// 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 (&):

use alloc_wg::string::String;

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.

use alloc_wg::string::String;

trait TraitExample {}

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

fn example_func<A: TraitExample>(example_arg: A) {}

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 alloc_wg::string::String;
use std::mem;

let story = String::from("Once upon a time...");
// Prevent automatically dropping the String's data
let mut story = mem::ManuallyDrop::new(story);

let ptr = story.as_mut_ptr();
let len = story.len();
let capacity = story.capacity();

// story has nineteen bytes
assert_eq!(19, len);

// 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, 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:

use alloc_wg::string::String;

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:

use alloc_wg::string::String;

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.

Implementations

impl String

#[must_use]pub const fn new() -> Self

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.

Examples

Basic usage:

use alloc_wg::string::String;

let s = String::new();

#[must_use]pub fn with_capacity(capacity: usize) -> Self

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:

use alloc_wg::string::String;

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 _ in 0..10 {
    s.push('a');
}

assert_eq!(s.capacity(), cap);

// ...but this may make the vector reallocate
s.push('a');

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

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

Examples

Basic usage:

use alloc_wg::string::String;

// 𝄞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());

#[must_use]pub fn from_utf16_lossy(v: &[u16]) -> Self

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:

use alloc_wg::string::String;

// 𝄞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
) -> Self

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 alloc_wg::string::String;
use std::mem;

unsafe {
    let s = String::from("hello");
    // Prevent automatically dropping the String's data
    let mut s = mem::ManuallyDrop::new(s);

    let ptr = s.as_mut_ptr();
    let len = s.len();
    let capacity = s.capacity();

    let s = String::from_raw_parts(ptr, len, capacity);

    assert_eq!(String::from("hello"), s);
}

impl<A: AllocRef> String<A>

pub fn new_in(a: A) -> Self

Like new but parameterized over the choice of allocator for the returned String.

pub fn with_capacity_in(capacity: usize, a: A) -> Self where
    A: AllocRef, 

Like with_capacity but parameterized over the choice of allocator for the returned String.

Panics

Panics if the allocation fails.

pub fn try_with_capacity_in(
    capacity: usize,
    a: A
) -> Result<Self, TryReserveError> where
    A: AllocRef, 

Like with_capacity_in but returns errors instead of panicking.

pub fn from_str_in(s: &str, a: A) -> Self

Like from_str but parameterized over the choice of allocator for the returned String.

Panics

Panics if the allocation fails.

pub fn try_from_str_in(s: &str, a: A) -> Result<Self, TryReserveError>

Like from_str_in but returns errors instead of panicking.

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

Converts a vector of bytes to a String.

A string (String) 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 into_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:

use alloc_wg::{string::String, vec};

// 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:

use alloc_wg::{string::String, vec};

// 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_in(v: &[u8], a: A) -> Self

Like from_utf8_lossy but parameterized over the choice of allocator for the returned String.

Panics

Panics if allocation fails.

pub fn try_from_utf8_lossy_in(v: &[u8], a: A) -> Result<Self, TryReserveError>

Like from_utf8_lossy_in but returns errors instead of panicking.

pub fn from_utf16_in(v: &[u16], a: A) -> Result<Self, FromUtf16Error>

Like from_utf16 but parameterized over the choice of allocator for the returned String.

pub fn into_raw_parts(self) -> (*mut u8, usize, usize)

Decomposes a String into its raw components.

Returns the raw pointer to the underlying data, the length of the string (in bytes), and the allocated capacity of the data (in bytes). These are the same arguments in the same order as the arguments to from_raw_parts.

After calling this function, the caller is responsible for the memory previously managed by the String. The only way to do this is to convert the raw pointer, length, and capacity back into a String with the from_raw_parts function, allowing the destructor to perform the cleanup.

Examples

use alloc_wg::string::String;

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

let (ptr, len, cap) = s.into_raw_parts();

let rebuilt = unsafe { String::from_raw_parts(ptr, len, cap) };
assert_eq!(rebuilt, "hello");

pub unsafe fn from_raw_parts_in(
    buf: *mut u8,
    length: usize,
    capacity: usize,
    alloc: A
) -> Self

Like from_raw_parts but parameterized over the choice of allocator for the returned String.

Safety

See from_raw_parts

pub unsafe fn from_utf8_unchecked(bytes: Vec<u8, A>) -> Self

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:

use alloc_wg::{string::String, vec};

// 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, A>

Converts a String into a byte vector.

This consumes the String, so we do not need to copy its contents.

Examples

Basic usage:

use alloc_wg::string::String;

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:

use alloc_wg::string::String;

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:

use alloc_wg::string::String;

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:

use alloc_wg::string::String;

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

s.push_str("bar");

assert_eq!("foobar", s);

Panics

Panics if the reallocation fails.

pub fn try_push_str(&mut self, string: &str) -> Result<(), TryReserveError>

Like push_str but returns errors instead of panicking.

pub fn capacity(&self) -> usize

Returns this String's capacity, in bytes.

Examples

Basic usage:

use alloc_wg::string::String;

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:

use alloc_wg::string::String;

let mut s = String::new();

s.reserve(10);

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

This may not actually increase the capacity:

use alloc_wg::string::String;

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:

use alloc_wg::string::String;

let mut s = String::new();

s.reserve_exact(10);

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

This may not actually increase the capacity:

use alloc_wg::string::String;

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 try_reserve(&mut self, additional: usize) -> Result<(), TryReserveError>

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

use alloc_wg::{collections::TryReserveError, string::String};

fn process_data(data: &str) -> Result<String, TryReserveError> {
    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)
}

pub fn try_reserve_exact(
    &mut self,
    additional: usize
) -> Result<(), TryReserveError>

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

use alloc_wg::{collections::TryReserveError, string::String};

fn process_data(data: &str) -> Result<String, TryReserveError> {
    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)
}

pub fn shrink_to_fit(&mut self)

Shrinks the capacity of this String to match its length.

Examples

Basic usage:

use alloc_wg::string::String;

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

s.reserve(100);
assert!(s.capacity() >= 100);

s.shrink_to_fit();
assert_eq!(3, s.capacity());

Panics

Panics if the reallocation fails

pub fn try_shrink_to_fit(&mut self) -> Result<(), TryReserveError>

Like shrink_to_fit but returns errors instead of panicking.

pub fn shrink_to(&mut self, min_capacity: usize)

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

use alloc_wg::string::String;

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);

Panics

• Panics if the given amount is larger than the current capacity.
• Panics if the reallocation fails.

pub fn try_shrink_to(
    &mut self,
    min_capacity: usize
) -> Result<(), TryReserveError>

Like shrink_to but returns errors instead of panicking.

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

Appends the given char to the end of this String.

Examples

Basic usage:

use alloc_wg::string::String;

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

s.push('1');
s.push('2');
s.push('3');

assert_eq!("abc123", s);

Panics

Panics if the reallocation fails.

pub fn try_push(&mut self, ch: char) -> Result<(), TryReserveError>

Like push but returns errors instead of panicking.

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:

use alloc_wg::string::String;

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:

use alloc_wg::string::String;

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:

use alloc_wg::string::String;

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:

use alloc_wg::string::String;

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, 

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, visiting each character exactly once in the original order, 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");

The exact order may be useful for tracking external state, like an index.

use alloc_wg::string::String;

let mut s = String::from("abcde");
let keep = [false, true, true, false, true];
let mut i = 0;
s.retain(|_| (keep[i], i += 1).0);
assert_eq!(s, "bce");

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:

use alloc_wg::string::String;

let mut s = String::with_capacity(3);

s.insert(0, 'f');
s.insert(1, 'o');
s.insert(2, 'o');

assert_eq!("foo", s);

Panics

Panics if reallocation fails.

pub fn try_insert(
    &mut self,
    idx: usize,
    ch: char
) -> Result<(), TryReserveError>

Like insert but returns errors instead of panicking.

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:

use alloc_wg::string::String;

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

s.insert_str(0, "foo");

assert_eq!("foobar", s);

Panics

Panics if the reallocation fails.

pub fn try_insert_str(
    &mut self,
    idx: usize,
    string: &str
) -> Result<(), TryReserveError>

Like insert_str but returns errors instead of panicking.

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

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:

use alloc_wg::string::String;

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, not chars or graphemes. In other words, it may not be what a human considers the length of the string.

Examples

Basic usage:

use alloc_wg::string::String;

let a = String::from("foo");
assert_eq!(a.len(), 3);

let fancy_f = String::from("ƒoo");
assert_eq!(fancy_f.len(), 4);
assert_eq!(fancy_f.chars().count(), 3);

pub fn is_empty(&self) -> bool

Returns true if this String has a length of zero, and false otherwise.

Examples

Basic usage:

use alloc_wg::string::String;

let mut v = String::new();
assert!(v.is_empty());

v.push('a');
assert!(!v.is_empty());

pub fn split_off(&mut self, at: usize) -> Self where
    A: AllocRef + Clone, 

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

use alloc_wg::string::String;

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

Panics

Panics if the allocation fails.

pub fn try_split_off(&mut self, at: usize) -> Result<Self, TryReserveError> where
    A: AllocRef + Clone, 

Like split_off but returns errors instead of panicking.

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");

let capacity = s.capacity();

s.clear();

assert!(s.is_empty());
assert_eq!(s.len(), 0);
assert_eq!(s.capacity(), capacity);

pub fn drain<R>(&mut self, range: R) -> Drain<'_, A> where
    R: RangeBounds<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 replace_range<R>(&mut self, range: R, replace_with: &str) where
    R: RangeBounds<usize>, 

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.

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");

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

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();

Panics

Panics if the reallocation fails.

pub fn try_into_boxed_str(self) -> Result<Box<str, A>, TryReserveError>

Like into_boxed_str but returns errors instead of panicking.

Trait Implementations

impl<A, '_> Add<&'_ str> for String<A> where
    A: AllocRef, 

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 = String::from(a) + b;

type Output = Self

The resulting type after applying the + operator.

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

Performs the + operation.

impl<A, '_> AddAssign<&'_ str> for String<A> where
    A: AllocRef, 

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<A: AllocRef> AsRef<[u8]> for String<A>

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

Performs the conversion.

impl<A: AllocRef> AsRef<str> for String<A>

fn as_ref(&self) -> &str

Performs the conversion.

impl<D: AllocRef> Borrow<str> for String<D>

fn borrow(&self) -> &str

Immutably borrows from an owned value.

impl<D: AllocRef> BorrowMut<str> for String<D>

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

Mutably borrows from an owned value.

impl<A> Clone for String<A> where
    A: AllocRef + Clone, 

#[must_use = "Cloning is expected to be expensive"]fn clone(&self) -> Self

Returns a copy of the value.

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

Performs copy-assignment from source.

impl<A: AllocRef, B: AllocRef> CloneIn<B> for String<A>

type Cloned = String<B>

#[must_use = "Cloning is expected to be expensive"]fn clone_in(&self, a: B) -> Self::Cloned

fn try_clone_in(&self, a: B) -> Result<Self::Cloned, TryReserveError>

impl<A: AllocRef> Debug for String<A>

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

Formats the value using the given formatter.

impl Default for String

#[must_use]fn default() -> Self

Creates an empty String.

impl<A: AllocRef> Deref for String<A>

type Target = str

The resulting type after dereferencing.

fn deref(&self) -> &str

Dereferences the value.

impl<A: AllocRef> DerefMut for String<A>

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

Mutably dereferences the value.

impl<A: AllocRef> Display for String<A>

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

Formats the value using the given formatter.

impl<A: Eq + AllocRef> Eq for String<A>

impl<'a, A: AllocRef> Extend<&'a char> for String<A>

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

Extends a collection with the contents of an iterator.

fn extend_one(&mut self, item: A)

🔬 This is a nightly-only experimental API. (extend_one)

Extends a collection with exactly one element.

fn extend_reserve(&mut self, additional: usize)

🔬 This is a nightly-only experimental API. (extend_one)

Reserves capacity in a collection for the given number of additional elements.

impl<'a, A: AllocRef> Extend<&'a str> for String<A>

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

Extends a collection with the contents of an iterator.

fn extend_one(&mut self, item: A)

🔬 This is a nightly-only experimental API. (extend_one)

Extends a collection with exactly one element.

fn extend_reserve(&mut self, additional: usize)

🔬 This is a nightly-only experimental API. (extend_one)

Reserves capacity in a collection for the given number of additional elements.

impl<'a, A> Extend<Cow<'a, str>> for String<A> where
    A: AllocRef, 

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

Extends a collection with the contents of an iterator.

fn extend_one(&mut self, item: A)

🔬 This is a nightly-only experimental API. (extend_one)

Extends a collection with exactly one element.

fn extend_reserve(&mut self, additional: usize)

🔬 This is a nightly-only experimental API. (extend_one)

Reserves capacity in a collection for the given number of additional elements.

impl<A, B> Extend<String<B>> for String<A> where
    A: AllocRef,
    B: AllocRef, 

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

Extends a collection with the contents of an iterator.

fn extend_one(&mut self, item: A)

🔬 This is a nightly-only experimental API. (extend_one)

Extends a collection with exactly one element.

fn extend_reserve(&mut self, additional: usize)

🔬 This is a nightly-only experimental API. (extend_one)

Reserves capacity in a collection for the given number of additional elements.

impl<A: AllocRef> Extend<char> for String<A>

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

Extends a collection with the contents of an iterator.

fn extend_one(&mut self, item: A)

🔬 This is a nightly-only experimental API. (extend_one)

Extends a collection with exactly one element.

fn extend_reserve(&mut self, additional: usize)

🔬 This is a nightly-only experimental API. (extend_one)

Reserves capacity in a collection for the given number of additional elements.

impl<'_> From<&'_ String<Global>> for String

#[must_use]fn from(s: &Self) -> Self

Performs the conversion.

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

#[must_use]fn from(s: &str) -> Self

Performs the conversion.

impl<'a, A: AllocRef> From<&'a String<A>> for Cow<'a, str>

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

Performs the conversion.

impl From<Box<str, Global>> for String

#[must_use]fn from(s: Box<str>) -> Self

Converts the given boxed str slice to a String. It is notable that the str slice is owned.

Examples

Basic usage:

let s1: String = String::from("hello world");
let s2 = s1.into_boxed_str();
let s3: String = String::from(s2);

assert_eq!("hello world", s3)

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

#[must_use]fn from(s: Cow<'a, str>) -> Self

Performs the conversion.

impl<A> From<String<A>> for Box<str, A> where
    A: AllocRef, 

fn from(s: String<A>) -> Self

Converts the given String to a boxed str slice that is owned.

Examples

Basic usage:

let s1: String = String::from("hello world");
let s2: Box<str> = Box::from(s1);
let s3: String = String::from(s2);

assert_eq!("hello world", s3)

impl<A: AllocRef> From<String<A>> for Vec<u8, A>

fn from(string: String<A>) -> Self

Converts the given String to a vector Vec that holds values of type u8.

Examples

Basic usage:

let s1 = String::from("hello world");
let v1 = Vec::from(s1);

for b in v1 {
    println!("{}", b);
}

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

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

Creates a value from an iterator.

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

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

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) -> Self

Creates a value from an iterator.

impl FromIterator<String<Global>> for String

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

Creates a value from an iterator.

impl FromIterator<char> for String

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

Creates a value from an iterator.

impl FromStr for String

type Err = Infallible

The associated error which can be returned from parsing.

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

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

impl<A: AllocRef> Hash for String<A>

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: AllocRef> Index<Range<usize>> for String<A>

type Output = str

The returned type after indexing.

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

Performs the indexing (container[index]) operation.

impl<A: AllocRef> Index<RangeFrom<usize>> for String<A>

type Output = str

The returned type after indexing.

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

Performs the indexing (container[index]) operation.

impl<A: AllocRef> Index<RangeFull> for String<A>

type Output = str

The returned type after indexing.

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

Performs the indexing (container[index]) operation.

impl<A: AllocRef> Index<RangeInclusive<usize>> for String<A>

type Output = str

The returned type after indexing.

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

Performs the indexing (container[index]) operation.

impl<A: AllocRef> Index<RangeTo<usize>> for String<A>

type Output = str

The returned type after indexing.

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

Performs the indexing (container[index]) operation.

impl<A: AllocRef> Index<RangeToInclusive<usize>> for String<A>

type Output = str

The returned type after indexing.

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

Performs the indexing (container[index]) operation.

impl<A: AllocRef> IndexMut<Range<usize>> for String<A>

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

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

impl<A: AllocRef> IndexMut<RangeFrom<usize>> for String<A>

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

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

impl<A: AllocRef> IndexMut<RangeFull> for String<A>

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

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

impl<A: AllocRef> IndexMut<RangeInclusive<usize>> for String<A>

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

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

impl<A: AllocRef> IndexMut<RangeTo<usize>> for String<A>

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

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

impl<A: AllocRef> IndexMut<RangeToInclusive<usize>> for String<A>

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

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

impl<A: Ord + AllocRef> Ord for String<A>

fn cmp(&self, other: &String<A>) -> Ordering

This method returns an Ordering between self and other.

#[must_use]fn max(self, other: Self) -> Self

Compares and returns the maximum of two values.

#[must_use]fn min(self, other: Self) -> Self

Compares and returns the minimum of two values.

#[must_use]fn clamp(self, min: Self, max: Self) -> Self

🔬 This is a nightly-only experimental API. (clamp)

Restrict a value to a certain interval.

impl<A: AllocRef, '_> PartialEq<&'_ str> for String<A>

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

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

#[must_use]fn ne(&self, other: &Rhs) -> bool

This method tests for !=.

impl<A: AllocRef, '_> PartialEq<Cow<'_, str>> for String<A>

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

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

#[must_use]fn ne(&self, other: &Rhs) -> bool

This method tests for !=.

impl<A: AllocRef> PartialEq<String<A>> for str

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

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

#[must_use]fn ne(&self, other: &Rhs) -> bool

This method tests for !=.

impl<A: AllocRef, '_> PartialEq<String<A>> for &'_ str

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

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

#[must_use]fn ne(&self, other: &Rhs) -> bool

This method tests for !=.

impl<A: AllocRef, '_> PartialEq<String<A>> for Cow<'_, str>

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

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

#[must_use]fn ne(&self, other: &Rhs) -> bool

This method tests for !=.

impl<A: AllocRef> PartialEq<String<A>> for String

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

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

#[must_use]fn ne(&self, other: &Rhs) -> bool

This method tests for !=.

impl<A: AllocRef, B: AllocRef> PartialEq<String<B>> for String<A>

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

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

#[must_use]fn ne(&self, other: &Rhs) -> bool

This method tests for !=.

impl<A: AllocRef> PartialEq<String> for String<A>

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

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

#[must_use]fn ne(&self, other: &Rhs) -> bool

This method tests for !=.

impl<A: AllocRef> PartialEq<str> for String<A>

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

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

#[must_use]fn ne(&self, other: &Rhs) -> bool

This method tests for !=.

impl<A: PartialOrd + AllocRef> PartialOrd<String<A>> for String<A>

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

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

fn lt(&self, other: &String<A>) -> bool

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

fn le(&self, other: &String<A>) -> bool

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

fn gt(&self, other: &String<A>) -> bool

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

fn ge(&self, other: &String<A>) -> bool

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

impl<A: AllocRef> StructuralEq for String<A>

impl<'a, A: AllocRef> TryExtend<&'a char> for String<A>

type Err = TryReserveError

fn try_extend<I: IntoIterator<Item = &'a char>>(
    &mut self,
    iter: I
) -> Result<(), Self::Err>

Extends a collection "fallibly" with the contents of an iterator.

impl<'a, A: AllocRef> TryExtend<&'a str> for String<A>

type Err = TryReserveError

fn try_extend<I: IntoIterator<Item = &'a str>>(
    &mut self,
    iter: I
) -> Result<(), Self::Err>

Extends a collection "fallibly" with the contents of an iterator.

impl<'a, A: AllocRef> TryExtend<Cow<'a, str>> for String<A>

type Err = TryReserveError

fn try_extend<I: IntoIterator<Item = Cow<'a, str>>>(
    &mut self,
    iter: I
) -> Result<(), Self::Err>

Extends a collection "fallibly" with the contents of an iterator.

impl<A: AllocRef, B: AllocRef> TryExtend<String<B>> for String<A>

type Err = TryReserveError

fn try_extend<I: IntoIterator<Item = String<B>>>(
    &mut self,
    iter: I
) -> Result<(), Self::Err>

Extends a collection "fallibly" with the contents of an iterator.

impl<A: AllocRef> TryExtend<char> for String<A>

type Err = TryReserveError

fn try_extend<I: IntoIterator<Item = char>>(
    &mut self,
    iter: I
) -> Result<(), Self::Err>

Extends a collection "fallibly" with the contents of an iterator.

impl<A: AllocRef> Write for String<A>

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

Writes a string slice 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.