Struct std::string::String
[−]
[src]
pub struct String {
// some fields omitted
}A UTF-8 encoded, growable string.
The String type is the most common string type that has ownership over the
contents of the string. It has a close relationship with its borrowed
counterpart, the primitive str.
Examples
You can create a String from a literal string with String::from:
let hello = String::from("Hello, world!");
You can append a [char] to a String with the push() method, and
append a &str with the push_str() method:
let mut hello = String::from("Hello, "); hello.push('w'); hello.push_str("orld!");
If you have a vector of UTF-8 bytes, you can create a String from it with
the from_utf8() method:
// some bytes, in a vector let sparkle_heart = vec![240, 159, 146, 150]; // We know these bytes are valid, so we'll use `unwrap()`. let sparkle_heart = String::from_utf8(sparkle_heart).unwrap(); assert_eq!("💖", sparkle_heart);
UTF-8
Strings are always valid UTF-8. This has a few implications, the first of
which is that if you need a non-UTF-8 string, consider OsString. It is
similar, but without the UTF-8 constraint. The second implication is that
you cannot index into a String:
let s = "hello"; println!("The first letter of s is {}", s[0]); // ERROR!!!
Indexing is intended to be a constant-time operation, but UTF-8 encoding
does not allow us to do this. Furtheremore, it's not clear what sort of
thing the index should return: a byte, a codepoint, or a grapheme cluster.
The as_bytes() and chars() methods return iterators over the first
two, respectively.
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 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
&strs as arguments unless they need a String for some specific reason.
Representation
A String is made up of three components: a pointer to some bytes, a
length, and a capacity. The pointer points to an internal buffer String
uses to store its data. The length is the number of bytes currently stored
in the buffer, and the capacity is the size of the buffer in bytes. As such,
the length will always be less than or equal to the capacity.
This buffer is always stored on the heap.
You can look at these with the as_ptr(), [len()], and [capacity()]
methods:
use std::mem; let story = String::from("Once upon a time..."); let ptr = story.as_ptr(); let len = story.len(); let capacity = story.capacity(); // story has thirteen bytes assert_eq!(19, len); // Now that we have our parts, we throw the story away. mem::forget(story); // We can re-build a String out of ptr, len, and capacity. This is all // unsafe becuase 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);
[len()]: # method.len
[capacity()]: # method.capacity
If a String has enough capacity, adding elements to it will not
re-allocate. For example, consider this program:
let mut s = String::new(); println!("{}", s.capacity()); for _ in 0..5 { s.push_str("hello"); println!("{}", s.capacity()); }
This will output the following:
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
fn new() -> String
Creates a new string buffer initialized with the empty string.
Examples
fn main() { #![allow(unused_mut)] let mut s = String::new(); }let mut s = String::new();
fn with_capacity(capacity: usize) -> String
Creates a new string buffer with the given capacity.
The string will be able to hold exactly capacity bytes without
reallocating. If capacity is 0, the string will not allocate.
Examples
fn main() { 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'); }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 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().
Failure
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:
fn main() { // 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); }// 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:
fn main() { // some invalid bytes, in a vector let sparkle_heart = vec![0, 159, 146, 150]; assert!(String::from_utf8(sparkle_heart).is_err()); }// 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.
A string slice (&str) is 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 string slices, however: &str requires
that it is 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.
If you need a &str instead of a String, consider
str::from_utf8().
Examples
Basic usage:
fn main() { // 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); }// 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:
fn main() { // some invalid bytes let input = b"Hello \xF0\x90\x80World"; let output = String::from_utf8_lossy(input); assert_eq!("Hello �World", output); }// 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 None
if v contains any invalid data.
Examples
fn main() { // 𝄞music let v = &[0xD834, 0xDD1E, 0x006d, 0x0075, 0x0073, 0x0069, 0x0063]; assert_eq!(String::from_utf16(v).unwrap(), "𝄞music".to_string()); // 𝄞mu<invalid>ic let v = &[0xD834, 0xDD1E, 0x006d, 0x0075, 0xD800, 0x0069, 0x0063]; assert!(String::from_utf16(v).is_err()); }// 𝄞music let v = &[0xD834, 0xDD1E, 0x006d, 0x0075, 0x0073, 0x0069, 0x0063]; assert_eq!(String::from_utf16(v).unwrap(), "𝄞music".to_string()); // 𝄞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
fn main() { // 𝄞mus<invalid>ic<invalid> let v = &[0xD834, 0xDD1E, 0x006d, 0x0075, 0x0073, 0xDD1E, 0x0069, 0x0063, 0xD834]; assert_eq!(String::from_utf16_lossy(v), "𝄞mus\u{FFFD}ic\u{FFFD}".to_string()); }// 𝄞mus<invalid>ic<invalid> let v = &[0xD834, 0xDD1E, 0x006d, 0x0075, 0x0073, 0xDD1E, 0x0069, 0x0063, 0xD834]; assert_eq!(String::from_utf16_lossy(v), "𝄞mus\u{FFFD}ic\u{FFFD}".to_string());
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 very unsafe because:
- We call
Vec::from_raw_partsto get aVec<u8>. Therefore, this function inherits all of its unsafety, see its documentation for the invariants it expects, they also apply to this function. - We assume that the
Veccontains valid UTF-8.
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.
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, undefined behavior
results, as the rest of Rust assumes that Strings are valid UTF-8.
Examples
Basic usage:
fn main() { // 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); }// 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>
Returns the underlying byte buffer, encoded as UTF-8.
Examples
fn main() { let s = String::from("hello"); let bytes = s.into_bytes(); assert_eq!(bytes, [104, 101, 108, 108, 111]); }let s = String::from("hello"); let bytes = s.into_bytes(); assert_eq!(bytes, [104, 101, 108, 108, 111]);
fn as_str(&self) -> &str
Extracts a string slice containing the entire string.
fn push_str(&mut self, string: &str)
Pushes the given string onto this string buffer.
Examples
fn main() { let mut s = String::from("foo"); s.push_str("bar"); assert_eq!(s, "foobar"); }let mut s = String::from("foo"); s.push_str("bar"); assert_eq!(s, "foobar");
fn capacity(&self) -> usize
Returns the number of bytes that this string buffer can hold without reallocating.
Examples
fn main() { let s = String::with_capacity(10); assert!(s.capacity() >= 10); }let s = String::with_capacity(10); assert!(s.capacity() >= 10);
fn reserve(&mut self, additional: usize)
Reserves capacity for at least additional more bytes to be inserted
in the given String. The collection may reserve more space to avoid
frequent reallocations.
Panics
Panics if the new capacity overflows usize.
Examples
fn main() { let mut s = String::new(); s.reserve(10); assert!(s.capacity() >= 10); }let mut s = String::new(); s.reserve(10); assert!(s.capacity() >= 10);
fn reserve_exact(&mut self, additional: usize)
Reserves the minimum capacity for exactly additional more bytes to be
inserted in the given String. 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.
Panics
Panics if the new capacity overflows usize.
Examples
fn main() { let mut s = String::new(); s.reserve_exact(10); assert!(s.capacity() >= 10); }let mut s = String::new(); s.reserve_exact(10); assert!(s.capacity() >= 10);
fn shrink_to_fit(&mut self)
Shrinks the capacity of this string buffer to match its length.
Examples
fn main() { let mut s = String::from("foo"); s.reserve(100); assert!(s.capacity() >= 100); s.shrink_to_fit(); assert_eq!(s.capacity(), 3); }let mut s = String::from("foo"); s.reserve(100); assert!(s.capacity() >= 100); s.shrink_to_fit(); assert_eq!(s.capacity(), 3);
fn push(&mut self, ch: char)
Adds the given character to the end of the string.
Examples
fn main() { let mut s = String::from("abc"); s.push('1'); s.push('2'); s.push('3'); assert_eq!(s, "abc123"); }let mut s = String::from("abc"); s.push('1'); s.push('2'); s.push('3'); assert_eq!(s, "abc123");
fn as_bytes(&self) -> &[u8]
Works with the underlying buffer as a byte slice.
Examples
fn main() { let s = String::from("hello"); assert_eq!(s.as_bytes(), [104, 101, 108, 108, 111]); }let s = String::from("hello"); assert_eq!(s.as_bytes(), [104, 101, 108, 108, 111]);
fn truncate(&mut self, new_len: usize)
Shortens a string to the specified length.
Panics
Panics if new_len > current length,
or if new_len is not a character boundary.
Examples
fn main() { let mut s = String::from("hello"); s.truncate(2); assert_eq!(s, "he"); }let mut s = String::from("hello"); s.truncate(2); assert_eq!(s, "he");
fn pop(&mut self) -> Option<char>
Removes the last character from the string buffer and returns it.
Returns None if this string buffer is empty.
Examples
fn main() { 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); }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 the character from the string buffer at byte position idx and
returns it.
Warning
This is an O(n) operation as it requires copying every element in the buffer.
Panics
If idx does not lie on a character boundary, or if it is out of
bounds, then this function will panic.
Examples
fn main() { let mut s = String::from("foo"); assert_eq!(s.remove(0), 'f'); assert_eq!(s.remove(1), 'o'); assert_eq!(s.remove(0), 'o'); }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 the string buffer at byte position idx.
Warning
This is an O(n) operation as it requires copying every element in the buffer.
Panics
If idx does not lie on a character boundary or is out of bounds, then
this function will panic.
unsafe fn as_mut_vec(&mut self) -> &mut Vec<u8>
Views the string buffer as a mutable sequence of bytes.
This is unsafe because it does not check to ensure that the resulting string will be valid UTF-8.
Examples
fn main() { let mut s = String::from("hello"); unsafe { let vec = s.as_mut_vec(); assert!(vec == &[104, 101, 108, 108, 111]); vec.reverse(); } assert_eq!(s, "olleh"); }let mut s = String::from("hello"); unsafe { let vec = s.as_mut_vec(); assert!(vec == &[104, 101, 108, 108, 111]); vec.reverse(); } assert_eq!(s, "olleh");
fn len(&self) -> usize
Returns the number of bytes in this string.
Examples
fn main() { let a = "foo".to_string(); assert_eq!(a.len(), 3); }let a = "foo".to_string(); assert_eq!(a.len(), 3);
fn is_empty(&self) -> bool
Returns true if the string contains no bytes
Examples
fn main() { let mut v = String::new(); assert!(v.is_empty()); v.push('a'); assert!(!v.is_empty()); }let mut v = String::new(); assert!(v.is_empty()); v.push('a'); assert!(!v.is_empty());
fn clear(&mut self)
Truncates the string, returning it to 0 length.
Examples
fn main() { let mut s = "foo".to_string(); s.clear(); assert!(s.is_empty()); }let mut s = "foo".to_string(); s.clear(); assert!(s.is_empty());
fn drain<R>(&mut self, range: R) -> Drain where R: RangeArgument<usize>
Create a draining iterator that removes the specified range in the string and yields the removed chars from start to end. The element range is removed even if the iterator is not consumed until the end.
Panics
Panics if the starting point or end point are not on character boundaries, or if they are out of bounds.
Examples
fn main() { 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, ""); }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>
Converts the string into Box<str>.
Note that this will drop any excess capacity.
fn into_boxed_slice(self) -> Box<str>
: renamed to into_boxed_str
Converts the string into Box<str>.
Note that this will drop any excess capacity.
Methods from Deref<Target=str>
fn len(&self) -> usize
Returns the length of self.
This length is 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:
fn main() { let len = "foo".len(); assert_eq!(3, len); let len = "ƒoo".len(); // fancy f! assert_eq!(4, len); }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 this slice has a length of zero bytes.
Examples
Basic usage:
fn main() { let s = ""; assert!(s.is_empty()); let s = "not empty"; assert!(!s.is_empty()); }let s = ""; assert!(s.is_empty()); let s = "not empty"; assert!(!s.is_empty());
fn is_char_boundary(&self, index: usize) -> bool
str_char #27754): it is unclear whether this method pulls its weight with the existence of the char_indices iterator or this method may want to be replaced with checked slicing
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
#![feature(str_char)] fn main() { 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)); }#![feature(str_char)] 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:
fn main() { let bytes = "bors".as_bytes(); assert_eq!(b"bors", bytes); }let bytes = "bors".as_bytes(); assert_eq!(b"bors", bytes);
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:
fn main() { let s = "Hello"; let ptr = s.as_ptr(); }let s = "Hello"; let ptr = s.as_ptr();
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 satisifed:
beginmust come beforeend.beginandendmust be bye positions within the string slice.beginandendmust lie on UTF-8 sequence boundaries.
Examples
Basic usage:
fn main() { 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)); } }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
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 satisifed:
beginmust come beforeend.beginandendmust be bye positions within the string slice.beginandendmust lie on UTF-8 sequence boundaries.
fn char_range_at(&self, start: usize) -> CharRange
str_char #27754): often replaced by char_indices, this method may be removed in favor of just char_at() or eventually removed altogether
Given a byte position, returns the next char and its index.
Panics
If i is greater than or equal to the length of the string.
If i is not the index of the beginning of a valid UTF-8 sequence.
Examples
This example manually iterates through the code points of a string;
this should normally be
done by .chars() or .char_indices().
#![feature(str_char)] use std::str::CharRange; let s = "中华Việt Nam"; let mut i = 0; while i < s.len() { let CharRange {ch, next} = s.char_range_at(i); println!("{}: {}", i, ch); i = next; }
This outputs:
0: 中
3: 华
6: V
7: i
8: e
9:
11:
13: t
14:
15: N
16: a
17: m
fn char_range_at_reverse(&self, start: usize) -> CharRange
str_char #27754): often replaced by char_indices, this method may be removed in favor of just char_at_reverse() or eventually removed altogether
Given a byte position, returns the previous char and its position.
Note that Unicode has many features, such as combining marks, ligatures, and direction marks, that need to be taken into account to correctly reverse a string.
Returns 0 for next index if called on start index 0.
Panics
If i is greater than the length of the string.
If i is not an index following a valid UTF-8 sequence.
Examples
This example manually iterates through the code points of a string;
this should normally be
done by .chars().rev() or .char_indices().
#![feature(str_char)] use std::str::CharRange; let s = "中华Việt Nam"; let mut i = s.len(); while i > 0 { let CharRange {ch, next} = s.char_range_at_reverse(i); println!("{}: {}", i, ch); i = next; }
This outputs:
18: m
17: a
16: N
15:
14: t
13:
11:
9: e
8: i
7: V
6: 华
3: 中
fn char_at(&self, i: usize) -> char
str_char #27754): frequently replaced by the chars() iterator, this method may be removed or possibly renamed in the future; it is normally replaced by chars/char_indices iterators or by getting the first char from a subslice
Given a byte position, returns the char at that position.
Panics
If i is greater than or equal to the length of the string.
If i is not the index of the beginning of a valid UTF-8 sequence.
Examples
#![feature(str_char)] fn main() { let s = "abπc"; assert_eq!(s.char_at(1), 'b'); assert_eq!(s.char_at(2), 'π'); assert_eq!(s.char_at(4), 'c'); }#![feature(str_char)] let s = "abπc"; assert_eq!(s.char_at(1), 'b'); assert_eq!(s.char_at(2), 'π'); assert_eq!(s.char_at(4), 'c');
fn char_at_reverse(&self, i: usize) -> char
str_char #27754): see char_at for more details, but reverse semantics are also somewhat unclear, especially with which cases generate panics
Given a byte position, returns the char at that position, counting
from the end.
Panics
If i is greater than the length of the string.
If i is not an index following a valid UTF-8 sequence.
Examples
#![feature(str_char)] fn main() { let s = "abπc"; assert_eq!(s.char_at_reverse(1), 'a'); assert_eq!(s.char_at_reverse(2), 'b'); assert_eq!(s.char_at_reverse(3), 'π'); }#![feature(str_char)] let s = "abπc"; assert_eq!(s.char_at_reverse(1), 'a'); assert_eq!(s.char_at_reverse(2), 'b'); assert_eq!(s.char_at_reverse(3), 'π');
fn slice_shift_char(&self) -> Option<(char, &str)>
str_char #27754): awaiting conventions about shifting and slices and may not be warranted with the existence of the chars and/or char_indices iterators
Retrieves the first char from a &str and returns it.
Note that a single Unicode character (grapheme cluster)
can be composed of multiple chars.
This does not allocate a new string; instead, it returns a slice that points one code point beyond the code point that was shifted.
None is returned if the slice is empty.
Examples
#![feature(str_char)] fn main() { let s = "Łódź"; // \u{141}o\u{301}dz\u{301} let (c, s1) = s.slice_shift_char().unwrap(); assert_eq!(c, 'Ł'); assert_eq!(s1, "ódź"); let (c, s2) = s1.slice_shift_char().unwrap(); assert_eq!(c, 'o'); assert_eq!(s2, "\u{301}dz\u{301}"); }#![feature(str_char)] let s = "Łódź"; // \u{141}o\u{301}dz\u{301} let (c, s1) = s.slice_shift_char().unwrap(); assert_eq!(c, 'Ł'); assert_eq!(s1, "ódź"); let (c, s2) = s1.slice_shift_char().unwrap(); assert_eq!(c, 'o'); assert_eq!(s2, "\u{301}dz\u{301}");
fn split_at(&self, mid: usize) -> (&str, &str)
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:
fn main() { let s = "Per Martin-Löf"; let (first, last) = s.split_at(3); assert_eq!("Per", first); assert_eq!(" Martin-Löf", last); }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)
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:
fn main() { let s = "Per Martin-Löf"; let (first, last) = s.split_at(3); assert_eq!("Per", first); assert_eq!(" Martin-Löf", last); }let s = "Per Martin-Löf"; let (first, last) = s.split_at(3); assert_eq!("Per", first); assert_eq!(" Martin-Löf", last);
fn chars(&self) -> Chars
Returns an iterator over the chars 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:
fn main() { 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()); }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, chars 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 chars 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 chars, as well as their byte positions.
The iterator yields tuples. The position is first, the char is
second.
Examples
Basic usage:
fn main() { 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()); }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, chars 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:
fn main() { 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()); }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
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:
fn main() { 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()); }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:
fn main() { 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()); }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:
fn main() { 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()); }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:
fn main() { 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()); }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
: use lines() instead now
An iterator over the lines of a string.
fn utf16_units(&self) -> Utf16Units
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>
Returns true if the given &str is a sub-slice of this string slice.
Returns false if it's not.
Examples
Basic usage:
fn main() { let bananas = "bananas"; assert!(bananas.contains("nana")); assert!(!bananas.contains("apples")); }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>
Returns true if the given &str is a prefix of this string slice.
Returns false if it's not.
Examples
Basic usage:
fn main() { let bananas = "bananas"; assert!(bananas.starts_with("bana")); assert!(!bananas.starts_with("nana")); }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::Searcher: ReverseSearcher<'a>
Returns true if the given &str is a suffix of this string slice.
Returns false if not.
Examples
Basic usage:
fn main() { let bananas = "bananas"; assert!(bananas.ends_with("anas")); assert!(!bananas.ends_with("nana")); }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>
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:
fn main() { 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)); }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:
fn main() { let s = "Löwe 老虎 Léopard"; assert_eq!(s.find(char::is_whitespace), Some(5)); assert_eq!(s.find(char::is_lowercase), Some(1)); }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:
fn main() { let s = "Löwe 老虎 Léopard"; let x: &[_] = &['1', '2']; assert_eq!(s.find(x), None); }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::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:
fn main() { let s = "Löwe 老虎 Léopard"; assert_eq!(s.rfind('L'), Some(13)); assert_eq!(s.rfind('é'), Some(14)); }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:
fn main() { let s = "Löwe 老虎 Léopard"; assert_eq!(s.rfind(char::is_whitespace), Some(12)); assert_eq!(s.rfind(char::is_lowercase), Some(20)); }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:
fn main() { let s = "Löwe 老虎 Léopard"; let x: &[_] = &['1', '2']; assert_eq!(s.rfind(x), None); }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>
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:
fn main() { 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"]); }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:
fn main() { let v: Vec<&str> = "abc1defXghi".split(|c| c == '1' || c == 'X').collect(); assert_eq!(v, ["abc", "def", "ghi"]); }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:
fn main() { let x = "||||a||b|c".to_string(); let d: Vec<_> = x.split('|').collect(); assert_eq!(d, &["", "", "", "", "a", "", "b", "c"]); }let x = "||||a||b|c".to_string(); let d: Vec<_> = x.split('|').collect(); assert_eq!(d, &["", "", "", "", "a", "", "b", "c"]);
This can lead to possibly surprising behavior when whitespace is used as the separator. This code is correct:
fn main() { let x = " a b c".to_string(); let d: Vec<_> = x.split(' ').collect(); assert_eq!(d, &["", "", "", "", "a", "", "b", "c"]); }let x = " a b c".to_string(); let d: Vec<_> = x.split(' ').collect(); assert_eq!(d, &["", "", "", "", "a", "", "b", "c"]);
It does not give you:
fn main() { assert_eq!(d, &["a", "b", "c"]); }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::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:
fn main() { 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"]); }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:
fn main() { let v: Vec<&str> = "abc1defXghi".rsplit(|c| c == '1' || c == 'X').collect(); assert_eq!(v, ["ghi", "def", "abc"]); }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>
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:
fn main() { 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", ""]); }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::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
fn main() { 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"]); }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, count: usize, pat: P) -> SplitN<'a, P> where P: Pattern<'a>
An iterator over substrings of the given string slice, separated by a
pattern, restricted to returning at most count items.
The last element returned, if any, will contain the remainder of the string slice.
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:
fn main() { 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, [""]); }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:
fn main() { let v: Vec<&str> = "abc1defXghi".splitn(2, |c| c == '1' || c == 'X').collect(); assert_eq!(v, ["abc", "defXghi"]); }let v: Vec<&str> = "abc1defXghi".splitn(2, |c| c == '1' || c == 'X').collect(); assert_eq!(v, ["abc", "defXghi"]);
fn rsplitn<'a, P>(&'a self, count: usize, pat: P) -> RSplitN<'a, P> where P: Pattern<'a>, P::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 count items.
The last element returned, if any, will contain the remainder of the string slice.
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:
fn main() { 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"]); }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:
fn main() { let v: Vec<&str> = "abc1defXghi".rsplitn(2, |c| c == '1' || c == 'X').collect(); assert_eq!(v, ["ghi", "abc1def"]); }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>
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:
fn main() { 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"]); }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::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:
fn main() { 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"]); }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>
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:
fn main() { 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` }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::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:
fn main() { 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` }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:
fn main() { let s = " Hello\tworld\t"; assert_eq!("Hello\tworld", s.trim()); }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.
Examples
Basic usage:
fn main() { let s = " Hello\tworld\t"; assert_eq!("Hello\tworld\t", s.trim_left()); }let s = " Hello\tworld\t"; assert_eq!("Hello\tworld\t", s.trim_left());
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.
Examples
Basic usage:
fn main() { let s = " Hello\tworld\t"; assert_eq!(" Hello\tworld", s.trim_right()); }let s = " Hello\tworld\t"; assert_eq!(" Hello\tworld", s.trim_right());
fn trim_matches<'a, P>(&'a self, pat: P) -> &'a str where P: Pattern<'a>, P::Searcher: DoubleEndedSearcher<'a>
Returns a string slice with all prefixes and suffixes that match a pattern repeatedly removed.
The pattern can be a &str, char, or a closure that determines
if a character matches.
Examples
Simple patterns:
fn main() { 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"); }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:
fn main() { assert_eq!("1foo1barXX".trim_matches(|c| c == '1' || c == 'X'), "foo1bar"); }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>
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.
Examples
Basic usage:
fn main() { 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"); }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::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.
Examples
Simple patterns:
fn main() { 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"); }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:
fn main() { assert_eq!("1fooX".trim_left_matches(|c| c == '1' || c == 'X'), "fooX"); }assert_eq!("1fooX".trim_left_matches(|c| c == '1' || c == 'X'), "fooX");
fn parse<F>(&self) -> Result<F, F::Err> where 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.
Failure
Will return Err if it's not possible to parse this string slice into
the desired type.
Example
Basic usage
fn main() { let four: u32 = "4".parse().unwrap(); assert_eq!(4, four); }let four: u32 = "4".parse().unwrap(); assert_eq!(4, four);
Using the 'turbofish' instead of annotationg four:
let four = "4".parse::<u32>(); assert_eq!(Ok(4), four);
Failing to parse:
fn main() { let nope = "j".parse::<u32>(); assert!(nope.is_err()); }let nope = "j".parse::<u32>(); assert!(nope.is_err());
fn replace(&self, from: &str, to: &str) -> String
Replaces all occurrences of one string with another.
replace creates a new String, and copies the data from this string slice into it.
While doing so, it attempts to find a sub-&str. If it finds it, it replaces it with
the replacement string slice.
Examples
Basic usage:
fn main() { let s = "this is old"; assert_eq!("this is new", s.replace("old", "new")); }let s = "this is old"; assert_eq!("this is new", s.replace("old", "new"));
When a &str isn't found:
let s = "this is old"; assert_eq!(s, s.replace("cookie monster", "little lamb"));
fn to_lowercase(&self) -> String
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.
Examples
Basic usage:
fn main() { let s = "HELLO"; assert_eq!("hello", s.to_lowercase()); }let s = "HELLO"; assert_eq!("hello", s.to_lowercase());
A tricky example, with sigma:
fn main() { 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()); }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:
fn main() { let new_year = "农历新年"; assert_eq!(new_year, new_year.to_lowercase()); }let new_year = "农历新年"; assert_eq!(new_year, new_year.to_lowercase());
fn to_uppercase(&self) -> String
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.
Examples
Basic usage:
fn main() { let s = "hello"; assert_eq!("HELLO", s.to_uppercase()); }let s = "hello"; assert_eq!("HELLO", s.to_uppercase());
Scripts without case are not changed:
fn main() { let new_year = "农历新年"; assert_eq!(new_year, new_year.to_uppercase()); }let new_year = "农历新年"; assert_eq!(new_year, new_year.to_uppercase());
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
Converts a Box<str> into a String without copying or allocating.
Examples
Basic usage:
fn main() { let string = String::from("birthday gift"); let boxed_str = string.clone().into_boxed_str(); assert_eq!(boxed_str.into_string(), string); }let string = String::from("birthday gift"); let boxed_str = string.clone().into_boxed_str(); assert_eq!(boxed_str.into_string(), string);
Trait Implementations
impl Borrow<str> for String
impl Clone for String
fn clone(&self) -> String
fn clone_from(&mut self, source: &String)
impl FromIterator<char> for String
fn from_iter<I>(iterable: I) -> String where I: IntoIterator<Item=char>
impl<'a> FromIterator<&'a str> for String
fn from_iter<I>(iterable: I) -> String where I: IntoIterator<Item=&'a str>
impl FromIterator<String> for String
fn from_iter<I>(iterable: I) -> String where I: IntoIterator<Item=String>
impl Extend<char> for String
fn extend<I>(&mut self, iterable: I) where I: IntoIterator<Item=char>
impl<'a> Extend<&'a char> for String
fn extend<I>(&mut self, iterable: I) where I: IntoIterator<Item=&'a char>
impl<'a> Extend<&'a str> for String
fn extend<I>(&mut self, iterable: I) where I: IntoIterator<Item=&'a str>
impl Extend<String> for String
fn extend<I>(&mut self, iterable: I) where I: IntoIterator<Item=String>
impl<'a, 'b> Pattern<'a> for &'b String
A convenience impl that delegates to the impl for &str