Struct std::string::String
[−]
[src]
pub struct String {
// some fields omitted
}1.0.0A 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 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
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:
fn main() { let s = String::new(); }let s = String::new();
fn with_capacity(capacity: usize) -> String
Creates a new empty String with a particular capacity.
Strings have an internal buffer to hold their data. The capacity is
the length of that buffer, and can be queried with the capacity()
method. This method creates an empty String, but one with an initial
buffer that can hold capacity bytes. This is useful when you may be
appending a bunch of data to the String, reducing the number of
reallocations it needs to do.
If the given capacity is 0, no allocation will occur, and this method
is identical to the new() method.
Examples
Basic usage:
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().
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:
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.
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:
fn main() { // 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); }// 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:
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 Err
if v contains any invalid data.
Examples
Basic usage:
fn main() { // 𝄞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()); }// 𝄞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:
fn main() { // 𝄞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)); }// 𝄞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
ptrneeds to have been previously allocated by the same allocator the standard library uses. lengthneeds to be less than or equal tocapacity.capacityneeds to be the correct value.
Violating these may cause problems like corrupting the allocator's internal datastructures.
Examples
Basic usage:
fn main() { 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); } }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 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>
Converts a String into a byte vector.
This consumes the String, so we do not need to copy its contents.
Examples
Basic usage:
fn main() { let s = String::from("hello"); let bytes = s.into_bytes(); assert_eq!(&[104, 101, 108, 108, 111][..], &bytes[..]); }let s = String::from("hello"); let bytes = s.into_bytes(); assert_eq!(&[104, 101, 108, 108, 111][..], &bytes[..]);
fn as_str(&self) -> &str1.7.0
Extracts a string slice containing the entire string.
fn as_mut_str(&mut self) -> &mut str1.7.0
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:
fn main() { let mut s = String::from("foo"); s.push_str("bar"); assert_eq!("foobar", s); }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:
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)
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:
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);
This may not actually increase the capacity:
fn main() { 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()); }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:
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);
This may not actually increase the capacity:
fn main() { 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()); }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:
fn main() { let mut s = String::from("foo"); s.reserve(100); assert!(s.capacity() >= 100); s.shrink_to_fit(); assert_eq!(3, s.capacity()); }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:
fn main() { let mut s = String::from("abc"); s.push('1'); s.push('2'); s.push('3'); assert_eq!("abc123", s); }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.
Examples
Basic usage:
fn main() { let s = String::from("hello"); assert_eq!(&[104, 101, 108, 108, 111], s.as_bytes()); }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.
Panics
Panics if new_len does not lie on a char boundary.
Examples
Basic usage:
fn main() { let mut s = String::from("hello"); s.truncate(2); assert_eq!("he", s); }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:
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 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:
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 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:
fn main() { let mut s = String::with_capacity(3); s.insert(0, 'f'); s.insert(1, 'o'); s.insert(2, 'o'); assert_eq!("foo", s); }let mut s = String::with_capacity(3); s.insert(0, 'f'); s.insert(1, 'o'); s.insert(2, 'o'); assert_eq!("foo", 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 Strings are valid UTF-8.
Examples
Basic usage:
fn main() { 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"); }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:
fn main() { let a = String::from("foo"); assert_eq!(a.len(), 3); }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:
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 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:
fn main() { let mut s = String::from("foo"); s.clear(); assert!(s.is_empty()); assert_eq!(0, s.len()); assert_eq!(3, s.capacity()); }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
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:
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>1.4.0
Converts this String into a Box<str>.
This will drop any excess capacity.
Examples
Basic usage:
fn main() { let s = String::from("hello"); let b = s.into_boxed_str(); }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 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) -> bool1.9.0
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
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)); }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 satisfied:
beginmust come beforeend.beginandendmust be byte 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 str1.5.0
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:
beginmust come beforeend.beginandendmust be byte positions within the string slice.beginandendmust lie on UTF-8 sequence boundaries.
fn char_range_at(&self, start: usize) -> CharRange
: use slicing plus chars() plus len_utf8
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)] #![allow(deprecated)] 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
: use slicing plus chars().rev() plus len_utf8
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)] #![allow(deprecated)] 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
: use slicing plus chars()
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() { #![allow(deprecated)] 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)] #![allow(deprecated)] 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
: use slicing plus chars().rev()
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() { #![allow(deprecated)] 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)] #![allow(deprecated)] 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)>
: use chars() plus Chars::as_str
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() { #![allow(deprecated)] 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)] #![allow(deprecated)] 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)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:
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)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:
fn main() { 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); }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 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) -> SplitWhitespace1.1.0
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:
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) -> EncodeUtf16
: renamed to encode_utf16
Returns an iterator of u16 over the string encoded as UTF-16.
fn encode_utf16(&self) -> EncodeUtf161.8.0
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>
Returns true if the given pattern matches a sub-slice of
this string slice.
Returns false if it does 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 pattern matches a prefix of this
string slice.
Returns false if it does 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 pattern matches a suffix of this
string slice.
Returns false if it does 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>1.2.0
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>1.2.0
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>1.5.0
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>1.5.0
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.
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:
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());
Directionality:
fn main() { let s = " English"; assert!(Some('E') == s.trim_left().chars().next()); let s = " עברית"; assert!(Some('ע') == s.trim_left().chars().next()); }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:
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());
Directionality:
fn main() { let s = "English "; assert!(Some('h') == s.trim_right().chars().rev().next()); let s = "עברית "; assert!(Some('ת') == s.trim_right().chars().rev().next()); }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::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.
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:
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.
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:
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.
Errors
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 annotating 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<'a, P>(&'a self, from: P, to: &str) -> String where 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:
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 the pattern doesn't match:
fn main() { let s = "this is old"; assert_eq!(s, s.replace("cookie monster", "little lamb")); }let s = "this is old"; assert_eq!(s, s.replace("cookie monster", "little lamb"));
fn to_lowercase(&self) -> String1.2.0
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.
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) -> String1.2.0
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.
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>) -> String1.4.0
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);