std::string::String
Struct std::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
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
:
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
String
s implement Deref
<Target=str>
, and so inherit all of str
's methods. In addition, this means that you can pass a String
to any function which takes a &str
by using an ampersand (&
):
fn takes_str(s: &str) { } let s = String::from("Hello"); takes_str(&s);
This will create a &str
from the String
and pass it in. This conversion is very inexpensive, and so generally, functions will accept &str
s as arguments unless they need a String
for some specific reason.
Representation
A String
is made up of three components: a pointer to some bytes, a length, and a capacity. The pointer points to an internal buffer String
uses to store its data. The length is the number of bytes currently stored in the buffer, and the capacity is the size of the buffer in bytes. As such, the length will always be less than or equal to the capacity.
This buffer is always stored on the heap.
You can look at these with the as_ptr
, len
, and capacity
methods:
use std::mem; let story = String::from("Once upon a time..."); let ptr = story.as_ptr(); let len = story.len(); let capacity = story.capacity(); // story has 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
[src]
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();
fn with_capacity(capacity: usize) -> String
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.
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');
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 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.
fn from_utf8_lossy(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);
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());
fn from_utf16_lossy(v: &[u16]) -> String
Decode a UTF-16 encoded vector v
into a string, replacing invalid data with the replacement character (U+FFFD).
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));
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 tocapacity
. -
capacity
needs to be the correct value.
Violating these may cause problems like corrupting the allocator's internal datastructures.
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); }
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 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);
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[..]);
fn as_str(&self) -> &str
1.7.0
Extracts a string slice containing the entire string.
fn as_mut_str(&mut self) -> &mut str
1.7.0
Extracts a string slice containing the entire string.
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);
fn capacity(&self) -> usize
Returns this String
's capacity, in bytes.
Examples
Basic usage:
let s = String::with_capacity(10); assert!(s.capacity() >= 10);
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());
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());
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());
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);
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());
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);
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);
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');
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);
fn insert_str(&mut self, idx: usize, string: &str)
1.16.0
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);
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 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");
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);
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());
fn split_off(&mut self, at: usize) -> String
1.16.0
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
let mut hello = String::from("Hello, World!"); let world = hello.split_off(7); assert_eq!(hello, "Hello, "); assert_eq!(world, "World!");
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());
fn drain<R>(&mut self, range: R) -> Drain where
R: RangeArgument<usize>,
1.6.0
R: RangeArgument<usize>,
Create a draining iterator that removes the specified range in the string and yields the removed chars.
Note: The element range is removed even if the iterator is not consumed until the end.
Panics
Panics if the starting point or end point do not lie on a char
boundary, or if they're out of bounds.
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, "");
fn into_boxed_str(self) -> Box<str>
1.4.0
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();
Methods from Deref<Target = str>
fn len(&self) -> usize
Returns the length of self
.
This length is in bytes, not char
s or graphemes. In other words, it may not be what a human considers the length of the string.
Examples
Basic usage:
let len = "foo".len(); assert_eq!(3, len); let len = "ƒoo".len(); // fancy f! assert_eq!(4, len);
fn is_empty(&self) -> bool
Returns true
if self
has a length of zero bytes.
Examples
Basic usage:
let s = ""; assert!(s.is_empty()); let s = "not empty"; assert!(!s.is_empty());
fn is_char_boundary(&self, index: usize) -> bool
1.9.0
Checks that index
-th byte lies at the start and/or end of a UTF-8 code point sequence.
The start and end of the string (when index == self.len()
) are considered to be boundaries.
Returns false
if index
is greater than self.len()
.
Examples
let s = "Löwe 老虎 Léopard"; assert!(s.is_char_boundary(0)); // start of `老` assert!(s.is_char_boundary(6)); assert!(s.is_char_boundary(s.len())); // second byte of `ö` assert!(!s.is_char_boundary(2)); // third byte of `老` assert!(!s.is_char_boundary(8));
fn as_bytes(&self) -> &[u8]
Converts a string slice to a byte slice.
Examples
Basic usage:
let bytes = "bors".as_bytes(); assert_eq!(b"bors", bytes);
unsafe fn as_bytes_mut(&mut self) -> &mut [u8]
Converts a mutable string slice to a mutable byte slice.
fn as_ptr(&self) -> *const u8
Converts a string slice to a raw pointer.
As string slices are a slice of bytes, the raw pointer points to a u8
. This pointer will be pointing to the first byte of the string slice.
Examples
Basic usage:
let s = "Hello"; let ptr = s.as_ptr();
fn get<I>(&self, i: I) -> Option<&<I as SliceIndex<str>>::Output> where
I: SliceIndex<str>,
I: SliceIndex<str>,
Returns a subslice of str
.
This is the non-panicking alternative to indexing the str
. Returns None
whenever equivalent indexing operation would panic.
Examples
let v = "????∈????"; assert_eq!(Some("????"), v.get(0..4)); assert!(v.get(1..).is_none()); assert!(v.get(..8).is_none()); assert!(v.get(..42).is_none());
fn get_mut<I>(&mut self, i: I) -> Option<&mut <I as SliceIndex<str>>::Output> where
I: SliceIndex<str>,
I: SliceIndex<str>,
Returns a mutable subslice of str
.
This is the non-panicking alternative to indexing the str
. Returns None
whenever equivalent indexing operation would panic.
Examples
let mut v = String::from("????∈????"); assert_eq!(Some("????"), v.get_mut(0..4).map(|v| &*v)); assert!(v.get_mut(1..).is_none()); assert!(v.get_mut(..8).is_none()); assert!(v.get_mut(..42).is_none());
unsafe fn get_unchecked<I>(&self, i: I) -> &<I as SliceIndex<str>>::Output where
I: SliceIndex<str>,
I: SliceIndex<str>,
Returns a unchecked subslice of str
.
This is the unchecked alternative to indexing the str
.
Safety
Callers of this function are responsible that these preconditions are satisfied:
- The starting index must come before the ending index;
- Indexes must be within bounds of the original slice;
- Indexes must lie on UTF-8 sequence boundaries.
Failing that, the returned string slice may reference invalid memory or violate the invariants communicated by the str
type.
Examples
let v = "????∈????"; unsafe { assert_eq!("????", v.get_unchecked(0..4)); assert_eq!("∈", v.get_unchecked(4..7)); assert_eq!("????", v.get_unchecked(7..11)); }
unsafe fn get_unchecked_mut<I>(
&mut self,
i: I
) -> &mut <I as SliceIndex<str>>::Output where
I: SliceIndex<str>,
&mut self,
i: I
) -> &mut <I as SliceIndex<str>>::Output where
I: SliceIndex<str>,
Returns a mutable, unchecked subslice of str
.
This is the unchecked alternative to indexing the str
.
Safety
Callers of this function are responsible that these preconditions are satisfied:
- The starting index must come before the ending index;
- Indexes must be within bounds of the original slice;
- Indexes must lie on UTF-8 sequence boundaries.
Failing that, the returned string slice may reference invalid memory or violate the invariants communicated by the str
type.
Examples
let mut v = String::from("????∈????"); unsafe { assert_eq!("????", v.get_unchecked_mut(0..4)); assert_eq!("∈", v.get_unchecked_mut(4..7)); assert_eq!("????", v.get_unchecked_mut(7..11)); }
unsafe fn slice_unchecked(&self, begin: usize, end: usize) -> &str
Creates a string slice from another string slice, bypassing safety checks.
This new slice goes from begin
to end
, including begin
but excluding end
.
To get a mutable string slice instead, see the slice_mut_unchecked
method.
Safety
Callers of this function are responsible that three preconditions are satisfied:
-
begin
must come beforeend
. -
begin
andend
must be byte positions within the string slice. -
begin
andend
must lie on UTF-8 sequence boundaries.
Examples
Basic usage:
let s = "Löwe 老虎 Léopard"; unsafe { assert_eq!("Löwe 老虎 Léopard", s.slice_unchecked(0, 21)); } let s = "Hello, world!"; unsafe { assert_eq!("world", s.slice_unchecked(7, 12)); }
unsafe fn slice_mut_unchecked(&mut self, begin: usize, end: usize) -> &mut str
1.5.0
Creates a string slice from another string slice, bypassing safety checks.
This new slice goes from begin
to end
, including begin
but excluding end
.
To get an immutable string slice instead, see the slice_unchecked
method.
Safety
Callers of this function are responsible that three preconditions are satisfied:
-
begin
must come beforeend
. -
begin
andend
must be byte positions within the string slice. -
begin
andend
must lie on UTF-8 sequence boundaries.
fn split_at(&self, mid: usize) -> (&str, &str)
1.4.0
Divide one string slice into two at an index.
The argument, mid
, should be a byte offset from the start of the string. It must also be on the boundary of a UTF-8 code point.
The two slices returned go from the start of the string slice to mid
, and from mid
to the end of the string slice.
To get mutable string slices instead, see the split_at_mut
method.
Panics
Panics if mid
is not on a UTF-8 code point boundary, or if it is beyond the last code point of the string slice.
Examples
Basic usage:
let s = "Per Martin-Löf"; let (first, last) = s.split_at(3); assert_eq!("Per", first); assert_eq!(" Martin-Löf", last);
fn split_at_mut(&mut self, mid: usize) -> (&mut str, &mut str)
1.4.0
Divide one mutable string slice into two at an index.
The argument, mid
, should be a byte offset from the start of the string. It must also be on the boundary of a UTF-8 code point.
The two slices returned go from the start of the string slice to mid
, and from mid
to the end of the string slice.
To get immutable string slices instead, see the split_at
method.
Panics
Panics if mid
is not on a UTF-8 code point boundary, or if it is beyond the last code point of the string slice.
Examples
Basic usage:
let mut s = "Per Martin-Löf".to_string(); let (first, last) = s.split_at_mut(3); assert_eq!("Per", first); assert_eq!(" Martin-Löf", last);
fn chars(&self) -> Chars
Returns an iterator over the char
s of a string slice.
As a string slice consists of valid UTF-8, we can iterate through a string slice by char
. This method returns such an iterator.
It's important to remember that char
represents a Unicode Scalar Value, and may not match your idea of what a 'character' is. Iteration over grapheme clusters may be what you actually want.
Examples
Basic usage:
let word = "goodbye"; let count = word.chars().count(); assert_eq!(7, count); let mut chars = word.chars(); assert_eq!(Some('g'), chars.next()); assert_eq!(Some('o'), chars.next()); assert_eq!(Some('o'), chars.next()); assert_eq!(Some('d'), chars.next()); assert_eq!(Some('b'), chars.next()); assert_eq!(Some('y'), chars.next()); assert_eq!(Some('e'), chars.next()); assert_eq!(None, chars.next());
Remember, char
s may not match your human intuition about characters:
let y = "y̆"; let mut chars = y.chars(); assert_eq!(Some('y'), chars.next()); // not 'y̆' assert_eq!(Some('\u{0306}'), chars.next()); assert_eq!(None, chars.next());
fn char_indices(&self) -> CharIndices
Returns an iterator over the char
s of a string slice, and their positions.
As a string slice consists of valid UTF-8, we can iterate through a string slice by char
. This method returns an iterator of both these char
s, as well as their byte positions.
The iterator yields tuples. The position is first, the char
is second.
Examples
Basic usage:
let word = "goodbye"; let count = word.char_indices().count(); assert_eq!(7, count); let mut char_indices = word.char_indices(); assert_eq!(Some((0, 'g')), char_indices.next()); assert_eq!(Some((1, 'o')), char_indices.next()); assert_eq!(Some((2, 'o')), char_indices.next()); assert_eq!(Some((3, 'd')), char_indices.next()); assert_eq!(Some((4, 'b')), char_indices.next()); assert_eq!(Some((5, 'y')), char_indices.next()); assert_eq!(Some((6, 'e')), char_indices.next()); assert_eq!(None, char_indices.next());
Remember, char
s may not match your human intuition about characters:
let y = "y̆"; let mut char_indices = y.char_indices(); assert_eq!(Some((0, 'y')), char_indices.next()); // not (0, 'y̆') assert_eq!(Some((1, '\u{0306}')), char_indices.next()); assert_eq!(None, char_indices.next());
fn bytes(&self) -> Bytes
An iterator over the bytes of a string slice.
As a string slice consists of a sequence of bytes, we can iterate through a string slice by byte. This method returns such an iterator.
Examples
Basic usage:
let mut bytes = "bors".bytes(); assert_eq!(Some(b'b'), bytes.next()); assert_eq!(Some(b'o'), bytes.next()); assert_eq!(Some(b'r'), bytes.next()); assert_eq!(Some(b's'), bytes.next()); assert_eq!(None, bytes.next());
fn split_whitespace(&self) -> SplitWhitespace
1.1.0
Split a string slice by whitespace.
The iterator returned will return string slices that are sub-slices of the original string slice, separated by any amount of whitespace.
'Whitespace' is defined according to the terms of the Unicode Derived Core Property White_Space
.
Examples
Basic usage:
let mut iter = "A few words".split_whitespace(); assert_eq!(Some("A"), iter.next()); assert_eq!(Some("few"), iter.next()); assert_eq!(Some("words"), iter.next()); assert_eq!(None, iter.next());
All kinds of whitespace are considered:
let mut iter = " Mary had\ta\u{2009}little \n\t lamb".split_whitespace(); assert_eq!(Some("Mary"), iter.next()); assert_eq!(Some("had"), iter.next()); assert_eq!(Some("a"), iter.next()); assert_eq!(Some("little"), iter.next()); assert_eq!(Some("lamb"), iter.next()); assert_eq!(None, iter.next());
fn lines(&self) -> Lines
An iterator over the lines of a string, as string slices.
Lines are ended with either a newline (\n
) or a carriage return with a line feed (\r\n
).
The final line ending is optional.
Examples
Basic usage:
let text = "foo\r\nbar\n\nbaz\n"; let mut lines = text.lines(); assert_eq!(Some("foo"), lines.next()); assert_eq!(Some("bar"), lines.next()); assert_eq!(Some(""), lines.next()); assert_eq!(Some("baz"), lines.next()); assert_eq!(None, lines.next());
The final line ending isn't required:
let text = "foo\nbar\n\r\nbaz"; let mut lines = text.lines(); assert_eq!(Some("foo"), lines.next()); assert_eq!(Some("bar"), lines.next()); assert_eq!(Some(""), lines.next()); assert_eq!(Some("baz"), lines.next()); assert_eq!(None, lines.next());
fn lines_any(&self) -> LinesAny
An iterator over the lines of a string.
fn encode_utf16(&self) -> EncodeUtf16
1.8.0
Returns an iterator of u16
over the string encoded as UTF-16.
fn contains<'a, P>(&'a self, pat: P) -> bool where
P: Pattern<'a>,
P: Pattern<'a>,
Returns true
if the given pattern matches a sub-slice of this string slice.
Returns false
if it does not.
Examples
Basic usage:
let bananas = "bananas"; assert!(bananas.contains("nana")); assert!(!bananas.contains("apples"));
fn starts_with<'a, P>(&'a self, pat: P) -> bool where
P: Pattern<'a>,
P: Pattern<'a>,
Returns true
if the given pattern matches a prefix of this string slice.
Returns false
if it does not.
Examples
Basic usage:
let bananas = "bananas"; assert!(bananas.starts_with("bana")); assert!(!bananas.starts_with("nana"));
fn ends_with<'a, P>(&'a self, pat: P) -> bool where
P: Pattern<'a>,
<P as Pattern<'a>>::Searcher: ReverseSearcher<'a>,
P: Pattern<'a>,
<P as Pattern<'a>>::Searcher: ReverseSearcher<'a>,
Returns true
if the given pattern matches a suffix of this string slice.
Returns false
if it does not.
Examples
Basic usage:
let bananas = "bananas"; assert!(bananas.ends_with("anas")); assert!(!bananas.ends_with("nana"));
fn find<'a, P>(&'a self, pat: P) -> Option<usize> where
P: Pattern<'a>,
P: Pattern<'a>,
Returns the byte index of the first character of this string slice that matches the pattern.
Returns None
if the pattern doesn't match.
The pattern can be a &str
, char
, or a closure that determines if a character matches.
Examples
Simple patterns:
let s = "Löwe 老虎 Léopard"; assert_eq!(s.find('L'), Some(0)); assert_eq!(s.find('é'), Some(14)); assert_eq!(s.find("Léopard"), Some(13));
More complex patterns with closures:
let s = "Löwe 老虎 Léopard"; assert_eq!(s.find(char::is_whitespace), Some(5)); assert_eq!(s.find(char::is_lowercase), Some(1));
Not finding the pattern:
let s = "Löwe 老虎 Léopard"; let x: &[_] = &['1', '2']; assert_eq!(s.find(x), None);
fn rfind<'a, P>(&'a self, pat: P) -> Option<usize> where
P: Pattern<'a>,
<P as Pattern<'a>>::Searcher: ReverseSearcher<'a>,
P: Pattern<'a>,
<P as Pattern<'a>>::Searcher: ReverseSearcher<'a>,
Returns the byte index of the last character of this string slice that matches the pattern.
Returns None
if the pattern doesn't match.
The pattern can be a &str
, char
, or a closure that determines if a character matches.
Examples
Simple patterns:
let s = "Löwe 老虎 Léopard"; assert_eq!(s.rfind('L'), Some(13)); assert_eq!(s.rfind('é'), Some(14));
More complex patterns with closures:
let s = "Löwe 老虎 Léopard"; assert_eq!(s.rfind(char::is_whitespace), Some(12)); assert_eq!(s.rfind(char::is_lowercase), Some(20));
Not finding the pattern:
let s = "Löwe 老虎 Léopard"; let x: &[_] = &['1', '2']; assert_eq!(s.rfind(x), None);
fn split<'a, P>(&'a self, pat: P) -> Split<'a, P> where
P: Pattern<'a>,
P: Pattern<'a>,
An iterator over substrings of this string slice, separated by characters matched by a pattern.
The pattern can be a &str
, char
, or a closure that determines the split.
Iterator behavior
The returned iterator will be a DoubleEndedIterator
if the pattern allows a reverse search and forward/reverse search yields the same elements. This is true for, eg, char
but not for &str
.
If the pattern allows a reverse search but its results might differ from a forward search, the rsplit
method can be used.
Examples
Simple patterns:
let v: Vec<&str> = "Mary had a little lamb".split(' ').collect(); assert_eq!(v, ["Mary", "had", "a", "little", "lamb"]); let v: Vec<&str> = "".split('X').collect(); assert_eq!(v, [""]); let v: Vec<&str> = "lionXXtigerXleopard".split('X').collect(); assert_eq!(v, ["lion", "", "tiger", "leopard"]); let v: Vec<&str> = "lion::tiger::leopard".split("::").collect(); assert_eq!(v, ["lion", "tiger", "leopard"]); let v: Vec<&str> = "abc1def2ghi".split(char::is_numeric).collect(); assert_eq!(v, ["abc", "def", "ghi"]); let v: Vec<&str> = "lionXtigerXleopard".split(char::is_uppercase).collect(); assert_eq!(v, ["lion", "tiger", "leopard"]);
A more complex pattern, using a closure:
let v: Vec<&str> = "abc1defXghi".split(|c| c == '1' || c == 'X').collect(); assert_eq!(v, ["abc", "def", "ghi"]);
If a string contains multiple contiguous separators, you will end up with empty strings in the output:
let x = "||||a||b|c".to_string(); let d: Vec<_> = x.split('|').collect(); assert_eq!(d, &["", "", "", "", "a", "", "b", "c"]);
Contiguous separators are separated by the empty string.
let x = "(///)".to_string(); let d: Vec<_> = x.split('/').collect();; assert_eq!(d, &["(", "", "", ")"]);
Separators at the start or end of a string are neighbored by empty strings.
let d: Vec<_> = "010".split("0").collect(); assert_eq!(d, &["", "1", ""]);
When the empty string is used as a separator, it separates every character in the string, along with the beginning and end of the string.
let f: Vec<_> = "rust".split("").collect(); assert_eq!(f, &["", "r", "u", "s", "t", ""]);
Contiguous separators can lead to possibly surprising behavior when whitespace is used as the separator. This code is correct:
let x = " a b c".to_string(); let d: Vec<_> = x.split(' ').collect(); assert_eq!(d, &["", "", "", "", "a", "", "b", "c"]);
It does not give you:
assert_eq!(d, &["a", "b", "c"]);
Use split_whitespace
for this behavior.
fn rsplit<'a, P>(&'a self, pat: P) -> RSplit<'a, P> where
P: Pattern<'a>,
<P as Pattern<'a>>::Searcher: ReverseSearcher<'a>,
P: Pattern<'a>,
<P as Pattern<'a>>::Searcher: ReverseSearcher<'a>,
An iterator over substrings of the given string slice, separated by characters matched by a pattern and yielded in reverse order.
The pattern can be a &str
, char
, or a closure that determines the split.
Iterator behavior
The returned iterator requires that the pattern supports a reverse search, and it will be a DoubleEndedIterator
if a forward/reverse search yields the same elements.
For iterating from the front, the split
method can be used.
Examples
Simple patterns:
let v: Vec<&str> = "Mary had a little lamb".rsplit(' ').collect(); assert_eq!(v, ["lamb", "little", "a", "had", "Mary"]); let v: Vec<&str> = "".rsplit('X').collect(); assert_eq!(v, [""]); let v: Vec<&str> = "lionXXtigerXleopard".rsplit('X').collect(); assert_eq!(v, ["leopard", "tiger", "", "lion"]); let v: Vec<&str> = "lion::tiger::leopard".rsplit("::").collect(); assert_eq!(v, ["leopard", "tiger", "lion"]);
A more complex pattern, using a closure:
let v: Vec<&str> = "abc1defXghi".rsplit(|c| c == '1' || c == 'X').collect(); assert_eq!(v, ["ghi", "def", "abc"]);
fn split_terminator<'a, P>(&'a self, pat: P) -> SplitTerminator<'a, P> where
P: Pattern<'a>,
P: Pattern<'a>,
An iterator over substrings of the given string slice, separated by characters matched by a pattern.
The pattern can be a &str
, char
, or a closure that determines the split.
Equivalent to split
, except that the trailing substring is skipped if empty.
This method can be used for string data that is terminated, rather than separated by a pattern.
Iterator behavior
The returned iterator will be a DoubleEndedIterator
if the pattern allows a reverse search and forward/reverse search yields the same elements. This is true for, eg, char
but not for &str
.
If the pattern allows a reverse search but its results might differ from a forward search, the rsplit_terminator
method can be used.
Examples
Basic usage:
let v: Vec<&str> = "A.B.".split_terminator('.').collect(); assert_eq!(v, ["A", "B"]); let v: Vec<&str> = "A..B..".split_terminator(".").collect(); assert_eq!(v, ["A", "", "B", ""]);
fn rsplit_terminator<'a, P>(&'a self, pat: P) -> RSplitTerminator<'a, P> where
P: Pattern<'a>,
<P as Pattern<'a>>::Searcher: ReverseSearcher<'a>,
P: Pattern<'a>,
<P as Pattern<'a>>::Searcher: ReverseSearcher<'a>,
An iterator over substrings of self
, separated by characters matched by a pattern and yielded in reverse order.
The pattern can be a simple &str
, char
, or a closure that determines the split. Additional libraries might provide more complex patterns like regular expressions.
Equivalent to split
, except that the trailing substring is skipped if empty.
This method can be used for string data that is terminated, rather than separated by a pattern.
Iterator behavior
The returned iterator requires that the pattern supports a reverse search, and it will be double ended if a forward/reverse search yields the same elements.
For iterating from the front, the split_terminator
method can be used.
Examples
let v: Vec<&str> = "A.B.".rsplit_terminator('.').collect(); assert_eq!(v, ["B", "A"]); let v: Vec<&str> = "A..B..".rsplit_terminator(".").collect(); assert_eq!(v, ["", "B", "", "A"]);
fn splitn<'a, P>(&'a self, n: usize, pat: P) -> SplitN<'a, P> where
P: Pattern<'a>,
P: Pattern<'a>,
An iterator over substrings of the given string slice, separated by a pattern, restricted to returning at most n
items.
If n
substrings are returned, the last substring (the n
th substring) will contain the remainder of the string.
The pattern can be a &str
, char
, or a closure that determines the split.
Iterator behavior
The returned iterator will not be double ended, because it is not efficient to support.
If the pattern allows a reverse search, the rsplitn
method can be used.
Examples
Simple patterns:
let v: Vec<&str> = "Mary had a little lambda".splitn(3, ' ').collect(); assert_eq!(v, ["Mary", "had", "a little lambda"]); let v: Vec<&str> = "lionXXtigerXleopard".splitn(3, "X").collect(); assert_eq!(v, ["lion", "", "tigerXleopard"]); let v: Vec<&str> = "abcXdef".splitn(1, 'X').collect(); assert_eq!(v, ["abcXdef"]); let v: Vec<&str> = "".splitn(1, 'X').collect(); assert_eq!(v, [""]);
A more complex pattern, using a closure:
let v: Vec<&str> = "abc1defXghi".splitn(2, |c| c == '1' || c == 'X').collect(); assert_eq!(v, ["abc", "defXghi"]);
fn rsplitn<'a, P>(&'a self, n: usize, pat: P) -> RSplitN<'a, P> where
P: Pattern<'a>,
<P as Pattern<'a>>::Searcher: ReverseSearcher<'a>,
P: Pattern<'a>,
<P as Pattern<'a>>::Searcher: ReverseSearcher<'a>,
An iterator over substrings of this string slice, separated by a pattern, starting from the end of the string, restricted to returning at most n
items.
If n
substrings are returned, the last substring (the n
th substring) will contain the remainder of the string.
The pattern can be a &str
, char
, or a closure that determines the split.
Iterator behavior
The returned iterator will not be double ended, because it is not efficient to support.
For splitting from the front, the splitn
method can be used.
Examples
Simple patterns:
let v: Vec<&str> = "Mary had a little lamb".rsplitn(3, ' ').collect(); assert_eq!(v, ["lamb", "little", "Mary had a"]); let v: Vec<&str> = "lionXXtigerXleopard".rsplitn(3, 'X').collect(); assert_eq!(v, ["leopard", "tiger", "lionX"]); let v: Vec<&str> = "lion::tiger::leopard".rsplitn(2, "::").collect(); assert_eq!(v, ["leopard", "lion::tiger"]);
A more complex pattern, using a closure:
let v: Vec<&str> = "abc1defXghi".rsplitn(2, |c| c == '1' || c == 'X').collect(); assert_eq!(v, ["ghi", "abc1def"]);
fn matches<'a, P>(&'a self, pat: P) -> Matches<'a, P> where
P: Pattern<'a>,
1.2.0
P: Pattern<'a>,
An iterator over the matches of a pattern within the given string slice.
The pattern can be a &str
, char
, or a closure that determines if a character matches.
Iterator behavior
The returned iterator will be a DoubleEndedIterator
if the pattern allows a reverse search and forward/reverse search yields the same elements. This is true for, eg, char
but not for &str
.
If the pattern allows a reverse search but its results might differ from a forward search, the rmatches
method can be used.
Examples
Basic usage:
let v: Vec<&str> = "abcXXXabcYYYabc".matches("abc").collect(); assert_eq!(v, ["abc", "abc", "abc"]); let v: Vec<&str> = "1abc2abc3".matches(char::is_numeric).collect(); assert_eq!(v, ["1", "2", "3"]);
fn rmatches<'a, P>(&'a self, pat: P) -> RMatches<'a, P> where
P: Pattern<'a>,
<P as Pattern<'a>>::Searcher: ReverseSearcher<'a>,
1.2.0
P: Pattern<'a>,
<P as Pattern<'a>>::Searcher: ReverseSearcher<'a>,
An iterator over the matches of a pattern within this string slice, yielded in reverse order.
The pattern can be a &str
, char
, or a closure that determines if a character matches.
Iterator behavior
The returned iterator requires that the pattern supports a reverse search, and it will be a DoubleEndedIterator
if a forward/reverse search yields the same elements.
For iterating from the front, the matches
method can be used.
Examples
Basic usage:
let v: Vec<&str> = "abcXXXabcYYYabc".rmatches("abc").collect(); assert_eq!(v, ["abc", "abc", "abc"]); let v: Vec<&str> = "1abc2abc3".rmatches(char::is_numeric).collect(); assert_eq!(v, ["3", "2", "1"]);
fn match_indices<'a, P>(&'a self, pat: P) -> MatchIndices<'a, P> where
P: Pattern<'a>,
1.5.0
P: Pattern<'a>,
An iterator over the disjoint matches of a pattern within this string slice as well as the index that the match starts at.
For matches of pat
within self
that overlap, only the indices corresponding to the first match are returned.
The pattern can be a &str
, char
, or a closure that determines if a character matches.
Iterator behavior
The returned iterator will be a DoubleEndedIterator
if the pattern allows a reverse search and forward/reverse search yields the same elements. This is true for, eg, char
but not for &str
.
If the pattern allows a reverse search but its results might differ from a forward search, the rmatch_indices
method can be used.
Examples
Basic usage:
let v: Vec<_> = "abcXXXabcYYYabc".match_indices("abc").collect(); assert_eq!(v, [(0, "abc"), (6, "abc"), (12, "abc")]); let v: Vec<_> = "1abcabc2".match_indices("abc").collect(); assert_eq!(v, [(1, "abc"), (4, "abc")]); let v: Vec<_> = "ababa".match_indices("aba").collect(); assert_eq!(v, [(0, "aba")]); // only the first `aba`
fn rmatch_indices<'a, P>(&'a self, pat: P) -> RMatchIndices<'a, P> where
P: Pattern<'a>,
<P as Pattern<'a>>::Searcher: ReverseSearcher<'a>,
1.5.0
P: Pattern<'a>,
<P as Pattern<'a>>::Searcher: ReverseSearcher<'a>,
An iterator over the disjoint matches of a pattern within self
, yielded in reverse order along with the index of the match.
For matches of pat
within self
that overlap, only the indices corresponding to the last match are returned.
The pattern can be a &str
, char
, or a closure that determines if a character matches.
Iterator behavior
The returned iterator requires that the pattern supports a reverse search, and it will be a DoubleEndedIterator
if a forward/reverse search yields the same elements.
For iterating from the front, the match_indices
method can be used.
Examples
Basic usage:
let v: Vec<_> = "abcXXXabcYYYabc".rmatch_indices("abc").collect(); assert_eq!(v, [(12, "abc"), (6, "abc"), (0, "abc")]); let v: Vec<_> = "1abcabc2".rmatch_indices("abc").collect(); assert_eq!(v, [(4, "abc"), (1, "abc")]); let v: Vec<_> = "ababa".rmatch_indices("aba").collect(); assert_eq!(v, [(2, "aba")]); // only the last `aba`
fn trim(&self) -> &str
Returns a string slice with leading and trailing whitespace removed.
'Whitespace' is defined according to the terms of the Unicode Derived Core Property White_Space
.
Examples
Basic usage:
let s = " Hello\tworld\t"; assert_eq!("Hello\tworld", s.trim());
fn trim_left(&self) -> &str
Returns a string slice with leading whitespace removed.
'Whitespace' is defined according to the terms of the Unicode Derived Core Property White_Space
.
Text directionality
A string is a sequence of bytes. 'Left' in this context means the first position of that byte string; for a language like Arabic or Hebrew which are 'right to left' rather than 'left to right', this will be the right side, not the left.
Examples
Basic usage:
let s = " Hello\tworld\t"; assert_eq!("Hello\tworld\t", s.trim_left());
Directionality:
let s = " English"; assert!(Some('E') == s.trim_left().chars().next()); let s = " עברית"; assert!(Some('ע') == s.trim_left().chars().next());
fn trim_right(&self) -> &str
Returns a string slice with trailing whitespace removed.
'Whitespace' is defined according to the terms of the Unicode Derived Core Property White_Space
.
Text directionality
A string is a sequence of bytes. 'Right' in this context means the last position of that byte string; for a language like Arabic or Hebrew which are 'right to left' rather than 'left to right', this will be the left side, not the right.
Examples
Basic usage:
let s = " Hello\tworld\t"; assert_eq!(" Hello\tworld", s.trim_right());
Directionality:
let s = "English "; assert!(Some('h') == s.trim_right().chars().rev().next()); let s = "עברית "; assert!(Some('ת') == s.trim_right().chars().rev().next());
fn trim_matches<'a, P>(&'a self, pat: P) -> &'a str where
P: Pattern<'a>,
<P as Pattern<'a>>::Searcher: DoubleEndedSearcher<'a>,
P: Pattern<'a>,
<P as Pattern<'a>>::Searcher: DoubleEndedSearcher<'a>,
Returns a string slice with all prefixes and suffixes that match a pattern repeatedly removed.
The pattern can be a char
or a closure that determines if a character matches.
Examples
Simple patterns:
assert_eq!("11foo1bar11".trim_matches('1'), "foo1bar"); assert_eq!("123foo1bar123".trim_matches(char::is_numeric), "foo1bar"); let x: &[_] = &['1', '2']; assert_eq!("12foo1bar12".trim_matches(x), "foo1bar");
A more complex pattern, using a closure:
assert_eq!("1foo1barXX".trim_matches(|c| c == '1' || c == 'X'), "foo1bar");
fn trim_left_matches<'a, P>(&'a self, pat: P) -> &'a str where
P: Pattern<'a>,
P: Pattern<'a>,
Returns a string slice with all prefixes that match a pattern repeatedly removed.
The pattern can be a &str
, char
, or a closure that determines if a character matches.
Text directionality
A string is a sequence of bytes. 'Left' in this context means the first position of that byte string; for a language like Arabic or Hebrew which are 'right to left' rather than 'left to right', this will be the right side, not the left.
Examples
Basic usage:
assert_eq!("11foo1bar11".trim_left_matches('1'), "foo1bar11"); assert_eq!("123foo1bar123".trim_left_matches(char::is_numeric), "foo1bar123"); let x: &[_] = &['1', '2']; assert_eq!("12foo1bar12".trim_left_matches(x), "foo1bar12");
fn trim_right_matches<'a, P>(&'a self, pat: P) -> &'a str where
P: Pattern<'a>,
<P as Pattern<'a>>::Searcher: ReverseSearcher<'a>,
P: Pattern<'a>,
<P as Pattern<'a>>::Searcher: ReverseSearcher<'a>,
Returns a string slice with all suffixes that match a pattern repeatedly removed.
The pattern can be a &str
, char
, or a closure that determines if a character matches.
Text directionality
A string is a sequence of bytes. 'Right' in this context means the last position of that byte string; for a language like Arabic or Hebrew which are 'right to left' rather than 'left to right', this will be the left side, not the right.
Examples
Simple patterns:
assert_eq!("11foo1bar11".trim_right_matches('1'), "11foo1bar"); assert_eq!("123foo1bar123".trim_right_matches(char::is_numeric), "123foo1bar"); let x: &[_] = &['1', '2']; assert_eq!("12foo1bar12".trim_right_matches(x), "12foo1bar");
A more complex pattern, using a closure:
assert_eq!("1fooX".trim_left_matches(|c| c == '1' || c == 'X'), "fooX");
fn parse<F>(&self) -> Result<F, <F as FromStr>::Err> where
F: FromStr,
F: FromStr,
Parses this string slice into another type.
Because parse
is so general, it can cause problems with type inference. As such, parse
is one of the few times you'll see the syntax affectionately known as the 'turbofish': ::<>
. This helps the inference algorithm understand specifically which type you're trying to parse into.
parse
can parse any type that implements the FromStr
trait.
Errors
Will return Err
if it's not possible to parse this string slice into the desired type.
Example
Basic usage
let four: u32 = "4".parse().unwrap(); assert_eq!(4, four);
Using the 'turbofish' instead of annotating four
:
let four = "4".parse::<u32>(); assert_eq!(Ok(4), four);
Failing to parse:
let nope = "j".parse::<u32>(); assert!(nope.is_err());
fn replace<'a, P>(&'a self, from: P, to: &str) -> String where
P: Pattern<'a>,
P: Pattern<'a>,
Replaces all matches of a pattern with another string.
replace
creates a new String
, and copies the data from this string slice into it. While doing so, it attempts to find matches of a pattern. If it finds any, it replaces them with the replacement string slice.
Examples
Basic usage:
let s = "this is old"; assert_eq!("this is new", s.replace("old", "new"));
When the pattern doesn't match:
let s = "this is old"; assert_eq!(s, s.replace("cookie monster", "little lamb"));
fn replacen<'a, P>(&'a self, pat: P, to: &str, count: usize) -> String where
P: Pattern<'a>,
1.16.0
P: Pattern<'a>,
Replaces first N matches of a pattern with another string.
replacen
creates a new String
, and copies the data from this string slice into it. While doing so, it attempts to find matches of a pattern. If it finds any, it replaces them with the replacement string slice at most count
times.
Examples
Basic usage:
let s = "foo foo 123 foo"; assert_eq!("new new 123 foo", s.replacen("foo", "new", 2)); assert_eq!("faa fao 123 foo", s.replacen('o', "a", 3)); assert_eq!("foo foo new23 foo", s.replacen(char::is_numeric, "new", 1));
When the pattern doesn't match:
let s = "this is old"; assert_eq!(s, s.replacen("cookie monster", "little lamb", 10));
fn to_lowercase(&self) -> String
1.2.0
Returns the lowercase equivalent of this string slice, as a new String
.
'Lowercase' is defined according to the terms of the Unicode Derived Core Property Lowercase
.
Since some characters can expand into multiple characters when changing the case, this function returns a String
instead of modifying the parameter in-place.
Examples
Basic usage:
let s = "HELLO"; assert_eq!("hello", s.to_lowercase());
A tricky example, with sigma:
let sigma = "Σ"; assert_eq!("σ", sigma.to_lowercase()); // but at the end of a word, it's ς, not σ: let odysseus = "ὈΔΥΣΣΕΎΣ"; assert_eq!("ὀδυσσεύς", odysseus.to_lowercase());
Languages without case are not changed:
let new_year = "农历新年"; assert_eq!(new_year, new_year.to_lowercase());
fn to_uppercase(&self) -> String
1.2.0
Returns the uppercase equivalent of this string slice, as a new String
.
'Uppercase' is defined according to the terms of the Unicode Derived Core Property Uppercase
.
Since some characters can expand into multiple characters when changing the case, this function returns a String
instead of modifying the parameter in-place.
Examples
Basic usage:
let s = "hello"; assert_eq!("HELLO", s.to_uppercase());
Scripts without case are not changed:
let new_year = "农历新年"; assert_eq!(new_year, new_year.to_uppercase());
fn escape_debug(&self) -> String
Escapes each char in s
with char::escape_debug
.
fn escape_default(&self) -> String
Escapes each char in s
with char::escape_default
.
fn escape_unicode(&self) -> String
Escapes each char in s
with char::escape_unicode
.
fn into_string(self: Box<str>) -> String
1.4.0
Converts a Box<str>
into a String
without copying or allocating.
Examples
Basic usage:
let string = String::from("birthday gift"); let boxed_str = string.clone().into_boxed_str(); assert_eq!(boxed_str.into_string(), string);
fn repeat(&self, n: usize) -> String
1.16.0
Create a String
by repeating a string n
times.
Examples
Basic usage:
assert_eq!("abc".repeat(4), String::from("abcabcabcabc"));
Trait Implementations
impl AsRef<str> for String
[src]
fn as_ref(&self) -> &str
Performs the conversion.
impl AsRef<[u8]> for String
[src]
fn as_ref(&self) -> &[u8]
Performs the conversion.
impl Write for String
[src]
fn write_str(&mut self, s: &str) -> Result<(), Error>
Writes a slice of bytes into this writer, returning whether the write succeeded. Read more
fn write_char(&mut self, c: char) -> Result<(), Error>
Writes a [char
] into this writer, returning whether the write succeeded. Read more
fn write_fmt(&mut self, args: Arguments) -> Result<(), Error>
Glue for usage of the [write!
] macro with implementors of this trait. Read more
impl FromIterator<char> for String
[src]
fn from_iter<I>(iter: I) -> String where
I: IntoIterator<Item = char>,
I: IntoIterator<Item = char>,
Creates a value from an iterator. Read more
impl<'a> FromIterator<&'a char> for String
1.17.0
[src]
fn from_iter<I>(iter: I) -> String where
I: IntoIterator<Item = &'a char>,
I: IntoIterator<Item = &'a char>,
Creates a value from an iterator. Read more
impl<'a> FromIterator<&'a str> for String
[src]
fn from_iter<I>(iter: I) -> String where
I: IntoIterator<Item = &'a str>,
I: IntoIterator<Item = &'a str>,
Creates a value from an iterator. Read more
impl FromIterator<String> for String
1.4.0
[src]
fn from_iter<I>(iter: I) -> String where
I: IntoIterator<Item = String>,
I: IntoIterator<Item = String>,
Creates a value from an iterator. Read more
impl Borrow<str> for String
[src]
fn borrow(&self) -> &str
Immutably borrows from an owned value. Read more
impl Debug for String
[src]
fn fmt(&self, f: &mut Formatter) -> Result<(), Error>
Formats the value using the given formatter.
impl<'a, 'b> Pattern<'a> for &'b String
[src]
A convenience impl that delegates to the impl for &str
type Searcher = <&'b str as Pattern<'a>>::Searcher
Associated searcher for this pattern
fn into_searcher(self, haystack: &'a str) -> <&'b str as Pattern<'a>>::Searcher
Constructs the associated searcher from self
and the haystack
to search in. Read more
fn is_contained_in(self, haystack: &'a str) -> bool
Checks whether the pattern matches anywhere in the haystack
fn is_prefix_of(self, haystack: &'a str) -> bool
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>,
Self::Searcher: ReverseSearcher<'a>,
Checks whether the pattern matches at the back of the haystack
impl<'a> AddAssign<&'a str> for String
1.12.0
[src]
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)
The method for the +=
operator
impl Into<Box<str>> for String
1.17.0
[src]
fn into(self) -> Box<str>
Performs the conversion.
impl Ord for String
[src]
fn cmp(&self, __arg_0: &String) -> Ordering
This method returns an Ordering
between self
and other
. Read more
impl ToString for String
1.17.0
[src]
fn to_string(&self) -> String
Converts the given value to a String
. Read more
impl Eq for String
[src]
impl Display for String
[src]
fn fmt(&self, f: &mut Formatter) -> Result<(), Error>
Formats the value using the given formatter. Read more
impl<'a> From<&'a str> for String
[src]
fn from(s: &'a str) -> String
Performs the conversion.
impl From<Box<str>> for String
1.17.0
[src]
fn from(s: Box<str>) -> String
Performs the conversion.
impl<'a> From<Cow<'a, str>> for String
1.14.0
[src]
fn from(s: Cow<'a, str>) -> String
Performs the conversion.
impl DerefMut for String
1.2.0
[src]
fn deref_mut(&mut self) -> &mut str
The method called to mutably dereference a value
impl Index<Range<usize>> for String
[src]
type Output = str
The returned type after indexing
fn index(&self, index: Range<usize>) -> &str
The method for the indexing (container[index]
) operation
impl Index<RangeTo<usize>> for String
[src]
type Output = str
The returned type after indexing
fn index(&self, index: RangeTo<usize>) -> &str
The method for the indexing (container[index]
) operation
impl Index<RangeFrom<usize>> for String
[src]
type Output = str
The returned type after indexing
fn index(&self, index: RangeFrom<usize>) -> &str
The method for the indexing (container[index]
) operation
impl Index<RangeFull> for String
[src]
type Output = str
The returned type after indexing
fn index(&self, _index: RangeFull) -> &str
The method for the indexing (container[index]
) operation
impl Index<RangeInclusive<usize>> for String
[src]
type Output = str
The returned type after indexing
fn index(&self, index: RangeInclusive<usize>) -> &str
The method for the indexing (container[index]
) operation
impl Index<RangeToInclusive<usize>> for String
[src]
type Output = str
The returned type after indexing
fn index(&self, index: RangeToInclusive<usize>) -> &str
The method for the indexing (container[index]
) operation
impl Clone for String
[src]
fn clone(&self) -> String
Returns a copy of the value. Read more
fn clone_from(&mut self, source: &String)
Performs copy-assignment from source
. Read more
impl PartialOrd<String> for String
[src]
fn partial_cmp(&self, __arg_0: &String) -> Option<Ordering>
This method returns an ordering between self
and other
values if one exists. Read more
fn lt(&self, __arg_0: &String) -> bool
This method tests less than (for self
and other
) and is used by the <
operator. Read more
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. Read more
fn gt(&self, __arg_0: &String) -> bool
This method tests greater than (for self
and other
) and is used by the >
operator. Read more
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. Read more
impl IndexMut<Range<usize>> for String
1.2.0
[src]
fn index_mut(&mut self, index: Range<usize>) -> &mut str
The method for the mutable indexing (container[index]
) operation
impl IndexMut<RangeTo<usize>> for String
1.2.0
[src]
fn index_mut(&mut self, index: RangeTo<usize>) -> &mut str
The method for the mutable indexing (container[index]
) operation
impl IndexMut<RangeFrom<usize>> for String
1.2.0
[src]
fn index_mut(&mut self, index: RangeFrom<usize>) -> &mut str
The method for the mutable indexing (container[index]
) operation
impl IndexMut<RangeFull> for String
1.2.0
[src]
fn index_mut(&mut self, _index: RangeFull) -> &mut str
The method for the mutable indexing (container[index]
) operation
impl IndexMut<RangeInclusive<usize>> for String
[src]
fn index_mut(&mut self, index: RangeInclusive<usize>) -> &mut str
The method for the mutable indexing (container[index]
) operation
impl IndexMut<RangeToInclusive<usize>> for String
[src]
fn index_mut(&mut self, index: RangeToInclusive<usize>) -> &mut str
The method for the mutable indexing (container[index]
) operation
impl Extend<char> for String
[src]
fn extend<I>(&mut self, iter: I) where
I: IntoIterator<Item = char>,
I: IntoIterator<Item = char>,
Extends a collection with the contents of an iterator. Read more
impl<'a> Extend<&'a char> for String
1.2.0
[src]
fn extend<I>(&mut self, iter: I) where
I: IntoIterator<Item = &'a char>,
I: IntoIterator<Item = &'a char>,
Extends a collection with the contents of an iterator. Read more
impl<'a> Extend<&'a str> for String
[src]
fn extend<I>(&mut self, iter: I) where
I: IntoIterator<Item = &'a str>,
I: IntoIterator<Item = &'a str>,
Extends a collection with the contents of an iterator. Read more
impl Extend<String> for String
1.4.0
[src]
fn extend<I>(&mut self, iter: I) where
I: IntoIterator<Item = String>,
I: IntoIterator<Item = String>,
Extends a collection with the contents of an iterator. Read more
impl Hash for String
[src]
fn hash<H>(&self, hasher: &mut H) where
H: Hasher,
H: Hasher,
Feeds this value into the given [Hasher
]. Read more
fn hash_slice<H>(data: &[Self], state: &mut H) where
H: Hasher,
1.3.0
H: Hasher,
Feeds a slice of this type into the given [Hasher
]. Read more
impl PartialEq<String> for String
[src]
fn eq(&self, other: &String) -> bool
This method tests for self
and other
values to be equal, and is used by ==
. Read more
fn ne(&self, other: &String) -> bool
This method tests for !=
.
impl<'a, 'b> PartialEq<str> for String
[src]
fn eq(&self, other: &str) -> bool
This method tests for self
and other
values to be equal, and is used by ==
. Read more
fn ne(&self, other: &str) -> bool
This method tests for !=
.
impl<'a, 'b> PartialEq<&'a str> for String
[src]
fn eq(&self, other: &&'a str) -> bool
This method tests for self
and other
values to be equal, and is used by ==
. Read more
fn ne(&self, other: &&'a str) -> bool
This method tests for !=
.
impl<'a, 'b> PartialEq<Cow<'a, str>> for String
[src]
fn eq(&self, other: &Cow<'a, str>) -> bool
This method tests for self
and other
values to be equal, and is used by ==
. Read more
fn ne(&self, other: &Cow<'a, str>) -> bool
This method tests for !=
.
impl<'a> Add<&'a str> for String
[src]
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;
type Output = String
The resulting type after applying the +
operator
fn add(self, other: &str) -> String
The method for the +
operator
impl Deref for String
[src]
type Target = str
The resulting type after dereferencing
fn deref(&self) -> &str
The method called to dereference a value
impl Default for String
[src]
fn default() -> String
Creates an empty String
.
impl FromStr for String
[src]
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. Read more
impl AsRef<OsStr> for String
[src]
fn as_ref(&self) -> &OsStr
Performs the conversion.
impl ToSocketAddrs for String
1.16.0
[src]
type Iter = IntoIter<SocketAddr>
Returned iterator over socket addresses which this type may correspond to. Read more
fn to_socket_addrs(&self) -> Result<IntoIter<SocketAddr>>
Converts this object to an iterator of resolved SocketAddr
s. Read more
impl AsRef<Path> for String
[src]
fn as_ref(&self) -> &Path
Performs the conversion.
© 2010 The Rust Project Developers
Licensed under the Apache License, Version 2.0 or the MIT license, at your option.
https://doc.rust-lang.org/std/string/struct.String.html