Struct CompactString

pub struct CompactString(/* private fields */);

A CompactString is a compact string type that can be used almost anywhere a String or str can be used.

Using CompactString

use compact_str::CompactString;

// CompactString auto derefs into a str so you can use all methods from `str`
// that take a `&self`
if CompactString::new("hello world!").is_ascii() {
    println!("we're all ASCII")
}

// You can use a CompactString in collections like you would a String or &str
let mut map: HashMap<CompactString, CompactString> = HashMap::new();

// directly construct a new `CompactString`
map.insert(CompactString::new("nyc"), CompactString::new("empire state building"));
// create a `CompactString` from a `&str`
map.insert("sf".into(), "transamerica pyramid".into());
// create a `CompactString` from a `String`
map.insert(String::from("sea").into(), String::from("space needle").into());

fn wrapped_print<T: AsRef<str>>(text: T) {
    println!("{}", text.as_ref());
}

// CompactString impls AsRef<str> and Borrow<str>, so it can be used anywhere
// that expects a generic string
if let Some(building) = map.get("nyc") {
    wrapped_print(building);
}

// CompactString can also be directly compared to a String or &str
assert_eq!(CompactString::new("chicago"), "chicago");
assert_eq!(CompactString::new("houston"), String::from("houston"));

Converting from a String

It’s important that a CompactString interops well with String, so you can easily use both in your code base.

CompactString implements From<String> and operates in the following manner:

• Eagerly inlines the string, possibly dropping excess capacity
• Otherwise re-uses the same underlying buffer from String

use compact_str::CompactString;

// eagerly inlining
let short = String::from("hello world");
let short_c = CompactString::from(short);
assert!(!short_c.is_heap_allocated());

// dropping excess capacity
let mut excess = String::with_capacity(256);
excess.push_str("abc");

let excess_c = CompactString::from(excess);
assert!(!excess_c.is_heap_allocated());
assert!(excess_c.capacity() < 256);

// re-using the same buffer
let long = String::from("this is a longer string that will be heap allocated");

let long_ptr = long.as_ptr();
let long_len = long.len();
let long_cap = long.capacity();

let mut long_c = CompactString::from(long);
assert!(long_c.is_heap_allocated());

let cpt_ptr = long_c.as_ptr();
let cpt_len = long_c.len();
let cpt_cap = long_c.capacity();

// the original String and the CompactString point to the same place in memory, buffer re-use!
assert_eq!(cpt_ptr, long_ptr);
assert_eq!(cpt_len, long_len);
assert_eq!(cpt_cap, long_cap);

Prevent Eagerly Inlining

A consequence of eagerly inlining is you then need to de-allocate the existing buffer, which might not always be desirable if you’re converting a very large amount of Strings. If your code is very sensitive to allocations, consider the CompactString::from_string_buffer API.

Implementations

impl CompactString

pub fn new<T>(text: T) -> CompactString

where T: AsRef<str>,

Creates a new CompactString from any type that implements AsRef<str>. If the string is short enough, then it will be inlined on the stack!

In a static or const context you can use the method CompactString::const_new().

Examples

Inlined

// We can inline strings up to 12 characters long on 32-bit architectures...
#[cfg(target_pointer_width = "32")]
let s = "i'm 12 chars";
// ...and up to 24 characters on 64-bit architectures!
#[cfg(target_pointer_width = "64")]
let s = "i am 24 characters long!";

let compact = CompactString::new(&s);

assert_eq!(compact, s);
// we are not allocated on the heap!
assert!(!compact.is_heap_allocated());

Heap

// For longer strings though, we get allocated on the heap
let long = "I am a longer string that will be allocated on the heap";
let compact = CompactString::new(long);

assert_eq!(compact, long);
// we are allocated on the heap!
assert!(compact.is_heap_allocated());

Creation

use compact_str::CompactString;

// Using a `&'static str`
let s = "hello world!";
let hello = CompactString::new(&s);

// Using a `String`
let u = String::from("🦄🌈");
let unicorn = CompactString::new(u);

// Using a `Box<str>`
let b: Box<str> = String::from("📦📦📦").into_boxed_str();
let boxed = CompactString::new(&b);

pub fn try_new<T>(text: T) -> Result<CompactString, ReserveError>

where T: AsRef<str>,

Fallible version of CompactString::new()

This method won’t panic if the system is out-of-memory, but return an [ReserveError]. Otherwise it behaves the same as CompactString::new().

pub const fn const_new(text: &'static str) -> CompactString

Creates a new inline CompactString from &'static str at compile time. Complexity: O(1). As an optimization, short strings get inlined.

In a dynamic context you can use the method CompactString::new().

Examples

use compact_str::CompactString;

const DEFAULT_NAME: CompactString = CompactString::const_new("untitled");

pub const fn new_inline(text: &'static str) -> CompactString

👎Deprecated since 0.8.0: replaced by CompactString::const_new, will be removed in 0.9.0

Creates a new inline CompactString at compile time.

pub const fn from_static_str(text: &'static str) -> CompactString

👎Deprecated since 0.8.0: replaced by CompactString::const_new, will be removed in 0.9.0

Creates a new inline CompactString from &'static str at compile time.

pub const fn as_static_str(&self) -> Option<&'static str>

Get back the &'static str constructed by CompactString::const_new.

If the string was short enough that it could be inlined, then it was inline, and this method will return None.

Examples

use compact_str::CompactString;

const DEFAULT_NAME: CompactString =
    CompactString::const_new("That is not dead which can eternal lie.");
assert_eq!(
    DEFAULT_NAME.as_static_str().unwrap(),
    "That is not dead which can eternal lie.",
);

pub fn with_capacity(capacity: usize) -> CompactString

Creates a new empty CompactString with the capacity to fit at least capacity bytes.

A CompactString will inline strings on the stack, if they’re small enough. Specifically, if the string has a length less than or equal to std::mem::size_of::<String> bytes then it will be inlined. This also means that CompactStrings have a minimum capacity of std::mem::size_of::<String>.

Panics

This method panics if the system is out-of-memory. Use CompactString::try_with_capacity() if you want to handle such a problem manually.

Examples

“zero” Capacity

// Creating a CompactString with a capacity of 0 will create
// one with capacity of std::mem::size_of::<String>();
let empty = CompactString::with_capacity(0);
let min_size = std::mem::size_of::<String>();

assert_eq!(empty.capacity(), min_size);
assert_ne!(0, min_size);
assert!(!empty.is_heap_allocated());

Max Inline Size

// Creating a CompactString with a capacity of std::mem::size_of::<String>()
// will not heap allocate.
let str_size = std::mem::size_of::<String>();
let empty = CompactString::with_capacity(str_size);

assert_eq!(empty.capacity(), str_size);
assert!(!empty.is_heap_allocated());

Heap Allocating

// If you create a `CompactString` with a capacity greater than
// `std::mem::size_of::<String>`, it will heap allocated. For heap
// allocated strings we have a minimum capacity

const MIN_HEAP_CAPACITY: usize = std::mem::size_of::<usize>() * 4;

let heap_size = std::mem::size_of::<String>() + 1;
let empty = CompactString::with_capacity(heap_size);

assert_eq!(empty.capacity(), MIN_HEAP_CAPACITY);
assert!(empty.is_heap_allocated());

pub fn try_with_capacity(capacity: usize) -> Result<CompactString, ReserveError>

Fallible version of CompactString::with_capacity()

This method won’t panic if the system is out-of-memory, but return an [ReserveError]. Otherwise it behaves the same as CompactString::with_capacity().

pub fn from_utf8<B>(buf: B) -> Result<CompactString, Utf8Error>

where B: AsRef<[u8]>,

Convert a slice of bytes into a CompactString.

A CompactString is a contiguous collection of bytes (u8s) that is valid UTF-8. This method converts from an arbitrary contiguous collection of bytes into a CompactString, failing if the provided bytes are not UTF-8.

Note: If you want to create a CompactString from a non-contiguous collection of bytes, enable the bytes feature of this crate, and see CompactString::from_utf8_buf

Examples

Valid UTF-8

let bytes = vec![240, 159, 166, 128, 240, 159, 146, 175];
let compact = CompactString::from_utf8(bytes).expect("valid UTF-8");

assert_eq!(compact, "🦀💯");

Invalid UTF-8

let bytes = vec![255, 255, 255];
let result = CompactString::from_utf8(bytes);

assert!(result.is_err());

pub unsafe fn from_utf8_unchecked<B>(buf: B) -> CompactString

where B: AsRef<[u8]>,

Converts a vector of bytes to a CompactString without checking that the string contains valid UTF-8.

See the safe version, CompactString::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 CompactString, as the rest of the standard library assumes that CompactStrings are valid UTF-8.

Examples

Basic usage:

// some bytes, in a vector
let sparkle_heart = vec![240, 159, 146, 150];

let sparkle_heart = unsafe {
    CompactString::from_utf8_unchecked(sparkle_heart)
};

assert_eq!("💖", sparkle_heart);

pub fn from_utf16<B>(buf: B) -> Result<CompactString, Utf16Error>

where B: AsRef<[u16]>,

Decode a UTF-16 slice of bytes into a CompactString, returning an Err if the slice contains any invalid data.

Examples

Valid UTF-16

let buf: &[u16] = &[0xD834, 0xDD1E, 0x006d, 0x0075, 0x0073, 0x0069, 0x0063];
let compact = CompactString::from_utf16(buf).unwrap();

assert_eq!(compact, "𝄞music");

Invalid UTF-16

let buf: &[u16] = &[0xD834, 0xDD1E, 0x006d, 0x0075, 0xD800, 0x0069, 0x0063];
let res = CompactString::from_utf16(buf);

assert!(res.is_err());

pub fn from_utf16_lossy<B>(buf: B) -> CompactString

where B: AsRef<[u16]>,

Decode a UTF-16–encoded slice v into a CompactString, replacing invalid data with the replacement character (U+FFFD), �.

Examples

Basic usage:

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

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

pub fn len(&self) -> usize

Returns the length of the CompactString in bytes, not chars or graphemes.

When using UTF-8 encoding (which all strings in Rust do) a single character will be 1 to 4 bytes long, therefore the return value of this method might not be what a human considers the length of the string.

Examples

let ascii = CompactString::new("hello world");
assert_eq!(ascii.len(), 11);

let emoji = CompactString::new("👱");
assert_eq!(emoji.len(), 4);

pub fn is_empty(&self) -> bool

Returns true if the CompactString has a length of 0, false otherwise

Examples

let mut msg = CompactString::new("");
assert!(msg.is_empty());

// add some characters
msg.push_str("hello reader!");
assert!(!msg.is_empty());

pub fn capacity(&self) -> usize

Returns the capacity of the CompactString, in bytes.

Note

• A CompactString will always have a capacity of at least std::mem::size_of::<String>()

Examples

Minimum Size

let min_size = std::mem::size_of::<String>();
let compact = CompactString::new("");

assert!(compact.capacity() >= min_size);

Heap Allocated

let compact = CompactString::with_capacity(128);
assert_eq!(compact.capacity(), 128);

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

Ensures that this CompactString’s capacity is at least additional bytes longer than its length. The capacity may be increased by more than additional bytes if it chooses, to prevent frequent reallocations.

Note

• A CompactString will always have at least a capacity of std::mem::size_of::<String>()
• Reserving additional bytes may cause the CompactString to become heap allocated

Panics

This method panics if the new capacity overflows usize or if the system is out-of-memory. Use CompactString::try_reserve() if you want to handle such a problem manually.

Examples

const WORD: usize = std::mem::size_of::<usize>();
let mut compact = CompactString::default();
assert!(compact.capacity() >= (WORD * 3) - 1);

compact.reserve(200);
assert!(compact.is_heap_allocated());
assert!(compact.capacity() >= 200);

pub fn try_reserve(&mut self, additional: usize) -> Result<(), ReserveError>

Fallible version of CompactString::reserve()

This method won’t panic if the system is out-of-memory, but return an [ReserveError] Otherwise it behaves the same as CompactString::reserve().

pub fn as_str(&self) -> &str

Returns a string slice containing the entire CompactString.

Examples

let s = CompactString::new("hello");

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

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

Returns a mutable string slice containing the entire CompactString.

Examples

let mut s = CompactString::new("hello");
s.as_mut_str().make_ascii_uppercase();

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

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

Returns a byte slice of the CompactString’s contents.

Examples

let s = CompactString::new("hello");

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

pub unsafe fn as_mut_bytes(&mut self) -> &mut [u8]

Provides a mutable reference to the underlying buffer of bytes.

Safety

• All Rust strings, including CompactString, must be valid UTF-8. The caller must guarantee that any modifications made to the underlying buffer are valid UTF-8.

Examples

let mut s = CompactString::new("hello");

let slice = unsafe { s.as_mut_bytes() };
// copy bytes into our string
slice[5..11].copy_from_slice(" world".as_bytes());
// set the len of the string
unsafe { s.set_len(11) };

assert_eq!(s, "hello world");

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

Appends the given char to the end of this CompactString.

Examples

let mut s = CompactString::new("foo");

s.push('b');
s.push('a');
s.push('r');

assert_eq!("foobar", s);

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

Removes the last character from the CompactString and returns it. Returns None if this CompactString is empty.

Examples

let mut s = CompactString::new("abc");

assert_eq!(s.pop(), Some('c'));
assert_eq!(s.pop(), Some('b'));
assert_eq!(s.pop(), Some('a'));

assert_eq!(s.pop(), None);

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

Appends a given string slice onto the end of this CompactString

Examples

let mut s = CompactString::new("abc");

s.push_str("123");

assert_eq!("abc123", s);

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

Removes a char from this CompactString 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 CompactString’s length, or if it does not lie on a char boundary.

Examples

Basic usage:

let mut c = CompactString::from("hello world");

assert_eq!(c.remove(0), 'h');
assert_eq!(c, "ello world");

assert_eq!(c.remove(5), 'w');
assert_eq!(c, "ello orld");

Past total length:

let mut c = CompactString::from("hello there!");
c.remove(100);

Not on char boundary:

let mut c = CompactString::from("🦄");
c.remove(1);

pub unsafe fn set_len(&mut self, new_len: usize)

Forces the length of the CompactString to new_len.

This is a low-level operation that maintains none of the normal invariants for CompactString. If you want to modify the CompactString you should use methods like push, push_str or pop.

Safety

• new_len must be less than or equal to capacity()
• The elements at old_len..new_len must be initialized

pub fn is_heap_allocated(&self) -> bool

Returns whether or not the CompactString is heap allocated.

Examples

Inlined

let hello = CompactString::new("hello world");

assert!(!hello.is_heap_allocated());

Heap Allocated

let msg = CompactString::new("this message will self destruct in 5, 4, 3, 2, 1 💥");

assert!(msg.is_heap_allocated());

pub fn replace_range( &mut self, range: impl RangeBounds<usize>, replace_with: &str, )

Removes the specified range in the CompactString, and replaces it with the given string. The given string doesn’t need to be the same length as the range.

Panics

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

Examples

Basic usage:

let mut s = CompactString::new("Hello, world!");

s.replace_range(7..12, "WORLD");
assert_eq!(s, "Hello, WORLD!");

s.replace_range(7..=11, "you");
assert_eq!(s, "Hello, you!");

s.replace_range(5.., "! Is it me you're looking for?");
assert_eq!(s, "Hello! Is it me you're looking for?");

pub fn repeat(&self, n: usize) -> CompactString

Creates a new CompactString by repeating a string n times.

Panics

This function will panic if the capacity would overflow.

Examples

Basic usage:

use compact_str::CompactString;
assert_eq!(CompactString::new("abc").repeat(4), CompactString::new("abcabcabcabc"));

A panic upon overflow:

use compact_str::CompactString;

// this will panic at runtime
let huge = CompactString::new("0123456789abcdef").repeat(usize::MAX);

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

Truncate the CompactString to a shorter length.

If the length of the CompactString is less or equal to new_len, the call is a no-op.

Calling this function does not change the capacity of the CompactString.

Panics

Panics if the new end of the string does not lie on a char boundary.

Examples

Basic usage:

let mut s = CompactString::new("Hello, world!");
s.truncate(5);
assert_eq!(s, "Hello");

pub fn as_ptr(&self) -> *const u8

Converts a CompactString to a raw pointer.

pub fn as_mut_ptr(&mut self) -> *mut u8

Converts a mutable CompactString to a raw pointer.

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

Insert string character at an index.

Examples

Basic usage:

let mut s = CompactString::new("Hello!");
s.insert_str(5, ", world");
assert_eq!(s, "Hello, world!");

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

Insert a character at an index.

Examples

Basic usage:

let mut s = CompactString::new("Hello world!");
s.insert(5, ',');
assert_eq!(s, "Hello, world!");

pub fn clear(&mut self)

Reduces the length of the CompactString to zero.

Calling this function does not change the capacity of the CompactString.

let mut s = CompactString::new("Rust is the most loved language on Stackoverflow!");
assert_eq!(s.capacity(), 49);

s.clear();

assert_eq!(s, "");
assert_eq!(s.capacity(), 49);

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

Split the CompactString into at the given byte index.

Calling this function does not change the capacity of the CompactString, unless the CompactString is backed by a &'static str.

Panics

Panics if at does not lie on a char boundary.

Basic usage:

let mut s = CompactString::const_new("Hello, world!");
let w = s.split_off(5);

assert_eq!(w, ", world!");
assert_eq!(s, "Hello");

pub fn drain(&mut self, range: impl RangeBounds<usize>) -> Drain<'_>

Remove a range from the CompactString, and return it as an iterator.

Calling this function does not change the capacity of the CompactString.

Panics

Panics if the start or end of the range does not lie on a char boundary.

Examples

Basic usage:

let mut s = CompactString::new("Hello, world!");

let mut d = s.drain(5..12);
assert_eq!(d.next(), Some(','));   // iterate over the extracted data
assert_eq!(d.as_str(), " world"); // or get the whole data as &str

// The iterator keeps a reference to `s`, so you have to drop() the iterator,
// before you can access `s` again.
drop(d);
assert_eq!(s, "Hello!");

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

Shrinks the capacity of this CompactString with a lower bound.

The resulting capactity is never less than the size of 3×usize, i.e. the capacity than can be inlined.

Examples

Basic usage:

let mut s = CompactString::with_capacity(100);
assert_eq!(s.capacity(), 100);

// if the capacity was already bigger than the argument, the call is a no-op
s.shrink_to(100);
assert_eq!(s.capacity(), 100);

s.shrink_to(50);
assert_eq!(s.capacity(), 50);

// if the string can be inlined, it is
s.shrink_to(10);
assert_eq!(s.capacity(), 3 * std::mem::size_of::<usize>());

pub fn shrink_to_fit(&mut self)

Shrinks the capacity of this CompactString to match its length.

The resulting capactity is never less than the size of 3×usize, i.e. the capacity than can be inlined.

This method is effectively the same as calling [string.shrink_to(0)].

Examples

Basic usage:

let mut s = CompactString::from("This is a string with more than 24 characters.");

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

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

let mut s = CompactString::from("short string");

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

s.shrink_to_fit();
assert_eq!(s.capacity(), 3 * std::mem::size_of::<usize>());

pub fn retain(&mut self, predicate: impl FnMut(char) -> bool)

Retains only the characters specified by the predicate.

The method iterates over the characters in the string and calls the predicate.

If the predicate returns false, then the character gets removed. If the predicate returns true, then the character is kept.

Examples

let mut s = CompactString::from("äb𝄞d€");

let keep = [false, true, true, false, true];
let mut iter = keep.iter();
s.retain(|_| *iter.next().unwrap());

assert_eq!(s, "b𝄞€");

pub fn from_utf8_lossy(v: &[u8]) -> CompactString

Decode a bytes slice as UTF-8 string, replacing any illegal codepoints

Examples

let chess_knight = b"\xf0\x9f\xa8\x84";

assert_eq!(
    "🨄",
    CompactString::from_utf8_lossy(chess_knight),
);

// For valid UTF-8 slices, this is the same as:
assert_eq!(
    "🨄",
    CompactString::new(std::str::from_utf8(chess_knight).unwrap()),
);

Incorrect bytes:

let broken = b"\xf0\x9f\xc8\x84";

assert_eq!(
    "�Ȅ",
    CompactString::from_utf8_lossy(broken),
);

// For invalid UTF-8 slices, this is an optimized implemented for:
assert_eq!(
    "�Ȅ",
    CompactString::from(String::from_utf8_lossy(broken)),
);

pub fn from_utf16le(v: impl AsRef<[u8]>) -> Result<CompactString, Utf16Error>

Decode a slice of bytes as UTF-16 encoded string, in little endian.

Errors

If the slice has an odd number of bytes, or if it did not contain valid UTF-16 characters, a [Utf16Error] is returned.

Examples

const DANCING_MEN: &[u8] = b"\x3d\xd8\x6f\xdc\x0d\x20\x42\x26\x0f\xfe";
let dancing_men = CompactString::from_utf16le(DANCING_MEN).unwrap();
assert_eq!(dancing_men, "👯‍♂️");

pub fn from_utf16be(v: impl AsRef<[u8]>) -> Result<CompactString, Utf16Error>

Decode a slice of bytes as UTF-16 encoded string, in big endian.

Errors

If the slice has an odd number of bytes, or if it did not contain valid UTF-16 characters, a [Utf16Error] is returned.

Examples

const DANCING_WOMEN: &[u8] = b"\xd8\x3d\xdc\x6f\x20\x0d\x26\x40\xfe\x0f";
let dancing_women = CompactString::from_utf16be(DANCING_WOMEN).unwrap();
assert_eq!(dancing_women, "👯‍♀️");

pub fn from_utf16le_lossy(v: impl AsRef<[u8]>) -> CompactString

Lossy decode a slice of bytes as UTF-16 encoded string, in little endian.

In this context “lossy” means that any broken characters in the input are replaced by the <REPLACEMENT CHARACTER> '�'. Please notice that, unlike UTF-8, UTF-16 is not self synchronizing. I.e. if a byte in the input is dropped, all following data is broken.

Examples

// A "random" bit was flipped in the 4th byte:
const DANCING_MEN: &[u8] = b"\x3d\xd8\x6f\xfc\x0d\x20\x42\x26\x0f\xfe";
let dancing_men = CompactString::from_utf16le_lossy(DANCING_MEN);
assert_eq!(dancing_men, "�\u{fc6f}\u{200d}♂️");

pub fn from_utf16be_lossy(v: impl AsRef<[u8]>) -> CompactString

Lossy decode a slice of bytes as UTF-16 encoded string, in big endian.

In this context “lossy” means that any broken characters in the input are replaced by the <REPLACEMENT CHARACTER> '�'. Please notice that, unlike UTF-8, UTF-16 is not self synchronizing. I.e. if a byte in the input is dropped, all following data is broken.

Examples

// A "random" bit was flipped in the 9th byte:
const DANCING_WOMEN: &[u8] = b"\xd8\x3d\xdc\x6f\x20\x0d\x26\x40\xde\x0f";
let dancing_women = CompactString::from_utf16be_lossy(DANCING_WOMEN);
assert_eq!(dancing_women, "👯\u{200d}♀�");

pub fn into_string(self) -> String

Convert the CompactString into a String.

Examples

let s = CompactString::new("Hello world");
let s = s.into_string();
assert_eq!(s, "Hello world");

pub fn from_string_buffer(s: String) -> CompactString

Convert a String into a CompactString without inlining.

Note: You probably don’t need to use this method, instead you should use From<String> which is implemented for CompactString.

This method exists incase your code is very sensitive to memory allocations. Normally when converting a String to a CompactString we’ll inline short strings onto the stack. But this results in Drop-ing the original String, which causes memory it owned on the heap to be deallocated. Instead when using this method, we always reuse the buffer that was previously owned by the String, so no trips to the allocator are needed.

Examples

Short Strings

use compact_str::CompactString;

let short = "hello world".to_string();
let c_heap = CompactString::from_string_buffer(short);

// using CompactString::from_string_buffer, we'll re-use the String's underlying buffer
assert!(c_heap.is_heap_allocated());

// note: when Clone-ing a short heap allocated string, we'll eagerly inline at that point
let c_inline = c_heap.clone();
assert!(!c_inline.is_heap_allocated());

assert_eq!(c_heap, c_inline);

Longer Strings

use compact_str::CompactString;

let x = "longer string that will be on the heap".to_string();
let c1 = CompactString::from(x);

let y = "longer string that will be on the heap".to_string();
let c2 = CompactString::from_string_buffer(y);

// for longer strings, we re-use the underlying String's buffer in both cases
assert!(c1.is_heap_allocated());
assert!(c2.is_heap_allocated());

Buffer Re-use

use compact_str::CompactString;

let og = "hello world".to_string();
let og_addr = og.as_ptr();

let mut c = CompactString::from_string_buffer(og);
let ex_addr = c.as_ptr();

// When converting to/from String and CompactString with from_string_buffer we always re-use
// the same underlying allocated memory/buffer
assert_eq!(og_addr, ex_addr);

let long = "this is a long string that will be on the heap".to_string();
let long_addr = long.as_ptr();

let mut long_c = CompactString::from(long);
let long_ex_addr = long_c.as_ptr();

// When converting to/from String and CompactString with From<String>, we'll also re-use the
// underlying buffer, if the string is long, otherwise when converting to CompactString we
// eagerly inline
assert_eq!(long_addr, long_ex_addr);

pub fn to_ascii_lowercase(&self) -> CompactString

Returns a copy of this string where each character is mapped to its ASCII lower case equivalent.

ASCII letters ‘A’ to ‘Z’ are mapped to ‘a’ to ‘z’, but non-ASCII letters are unchanged.

To lowercase the value in-place, use str::make_ascii_lowercase.

To lowercase ASCII characters in addition to non-ASCII characters, use CompactString::to_lowercase.

Examples

use compact_str::CompactString;
let s = CompactString::new("Grüße, Jürgen ❤");

assert_eq!("grüße, jürgen ❤", s.to_ascii_lowercase());

pub fn to_ascii_uppercase(&self) -> CompactString

Returns a copy of this string where each character is mapped to its ASCII upper case equivalent.

ASCII letters ‘a’ to ‘z’ are mapped to ‘A’ to ‘Z’, but non-ASCII letters are unchanged.

To uppercase the value in-place, use str::make_ascii_uppercase.

To uppercase ASCII characters in addition to non-ASCII characters, use CompactString::to_uppercase.

Examples

use compact_str::CompactString;
let s = CompactString::new("Grüße, Jürgen ❤");

assert_eq!("GRüßE, JüRGEN ❤", s.to_ascii_uppercase());

pub fn to_lowercase(&self) -> CompactString

Returns the lowercase equivalent of this string slice, as a new CompactString.

‘Lowercase’ is defined according to the terms of the Unicode Derived Core Property Lowercase.

Since some characters can expand into multiple characters when changing the case, this function returns a CompactString instead of modifying the parameter in-place.

Examples

Basic usage:

use compact_str::CompactString;
let s = CompactString::new("HELLO");

assert_eq!("hello", s.to_lowercase());

A tricky example, with sigma:

use compact_str::CompactString;
let sigma = CompactString::new("Σ");

assert_eq!("σ", sigma.to_lowercase());

// but at the end of a word, it's ς, not σ:
let odysseus = CompactString::new("ὈΔΥΣΣΕΎΣ");

assert_eq!("ὀδυσσεύς", odysseus.to_lowercase());

Languages without case are not changed:

use compact_str::CompactString;
let new_year = CompactString::new("农历新年");

assert_eq!(new_year, new_year.to_lowercase());

pub fn from_str_to_lowercase(input: &str) -> CompactString

Returns the lowercase equivalent of this string slice, as a new CompactString.

‘Lowercase’ is defined according to the terms of the Unicode Derived Core Property Lowercase.

Since some characters can expand into multiple characters when changing the case, this function returns a CompactString instead of modifying the parameter in-place.

Examples

Basic usage:

use compact_str::CompactString;

assert_eq!("hello", CompactString::from_str_to_lowercase("HELLO"));

A tricky example, with sigma:

use compact_str::CompactString;

assert_eq!("σ", CompactString::from_str_to_lowercase("Σ"));

// but at the end of a word, it's ς, not σ:
assert_eq!("ὀδυσσεύς", CompactString::from_str_to_lowercase("ὈΔΥΣΣΕΎΣ"));

Languages without case are not changed:

use compact_str::CompactString;

let new_year = "农历新年";
assert_eq!(new_year, CompactString::from_str_to_lowercase(new_year));

pub fn to_uppercase(&self) -> CompactString

Returns the uppercase equivalent of this string slice, as a new CompactString.

‘Uppercase’ is defined according to the terms of the Unicode Derived Core Property Uppercase.

Since some characters can expand into multiple characters when changing the case, this function returns a CompactString instead of modifying the parameter in-place.

Examples

Basic usage:

use compact_str::CompactString;
let s = CompactString::new("hello");

assert_eq!("HELLO", s.to_uppercase());

Scripts without case are not changed:

use compact_str::CompactString;
let new_year = CompactString::new("农历新年");

assert_eq!(new_year, new_year.to_uppercase());

One character can become multiple:

use compact_str::CompactString;
let s = CompactString::new("tschüß");

assert_eq!("TSCHÜSS", s.to_uppercase());

pub fn from_str_to_uppercase(input: &str) -> CompactString

Returns the uppercase equivalent of this string slice, as a new CompactString.

‘Uppercase’ is defined according to the terms of the Unicode Derived Core Property Uppercase.

Since some characters can expand into multiple characters when changing the case, this function returns a CompactString instead of modifying the parameter in-place.

Examples

Basic usage:

use compact_str::CompactString;

assert_eq!("HELLO", CompactString::from_str_to_uppercase("hello"));

Scripts without case are not changed:

use compact_str::CompactString;

let new_year = "农历新年";
assert_eq!(new_year, CompactString::from_str_to_uppercase(new_year));

One character can become multiple:

use compact_str::CompactString;

assert_eq!("TSCHÜSS", CompactString::from_str_to_uppercase("tschüß"));

Methods from Deref<Target = str>

pub fn len(&self) -> usize

Returns the length of self.

This length is in bytes, not chars or graphemes. In other words, it might not be what a human considers the length of the string.

Examples

let len = "foo".len();
assert_eq!(3, len);

assert_eq!("ƒoo".len(), 4); // fancy f!
assert_eq!("ƒoo".chars().count(), 3);

pub fn is_empty(&self) -> bool

Returns true if self has a length of zero bytes.

Examples

let s = "";
assert!(s.is_empty());

let s = "not empty";
assert!(!s.is_empty());

pub fn is_char_boundary(&self, index: usize) -> bool

Checks that index-th byte is the first byte in a UTF-8 code point sequence or the end of the string.

The start and end of the string (when index == self.len()) are considered to be boundaries.

Returns false if index is greater than self.len().

Examples

let s = "Löwe 老虎 Léopard";
assert!(s.is_char_boundary(0));
// start of `老`
assert!(s.is_char_boundary(6));
assert!(s.is_char_boundary(s.len()));

// second byte of `ö`
assert!(!s.is_char_boundary(2));

// third byte of `老`
assert!(!s.is_char_boundary(8));

pub fn floor_char_boundary(&self, index: usize) -> usize

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

Finds the closest x not exceeding index where is_char_boundary(x) is true.

This method can help you truncate a string so that it’s still valid UTF-8, but doesn’t exceed a given number of bytes. Note that this is done purely at the character level and can still visually split graphemes, even though the underlying characters aren’t split. For example, the emoji 🧑‍🔬 (scientist) could be split so that the string only includes 🧑 (person) instead.

Examples

#![feature(round_char_boundary)]
let s = "❤️🧡💛💚💙💜";
assert_eq!(s.len(), 26);
assert!(!s.is_char_boundary(13));

let closest = s.floor_char_boundary(13);
assert_eq!(closest, 10);
assert_eq!(&s[..closest], "❤️🧡");

pub fn ceil_char_boundary(&self, index: usize) -> usize

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

Finds the closest x not below index where is_char_boundary(x) is true.

If index is greater than the length of the string, this returns the length of the string.

This method is the natural complement to floor_char_boundary. See that method for more details.

Examples

#![feature(round_char_boundary)]
let s = "❤️🧡💛💚💙💜";
assert_eq!(s.len(), 26);
assert!(!s.is_char_boundary(13));

let closest = s.ceil_char_boundary(13);
assert_eq!(closest, 14);
assert_eq!(&s[..closest], "❤️🧡💛");

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

Converts a string slice to a byte slice. To convert the byte slice back into a string slice, use the from_utf8 function.

Examples

let bytes = "bors".as_bytes();
assert_eq!(b"bors", bytes);

pub unsafe fn as_bytes_mut(&mut self) -> &mut [u8]

Converts a mutable string slice to a mutable byte slice.

Safety

The caller must ensure that the content of the slice is valid UTF-8 before the borrow ends and the underlying str is used.

Use of a str whose contents are not valid UTF-8 is undefined behavior.

Examples

Basic usage:

let mut s = String::from("Hello");
let bytes = unsafe { s.as_bytes_mut() };

assert_eq!(b"Hello", bytes);

Mutability:

let mut s = String::from("🗻∈🌏");

unsafe {
    let bytes = s.as_bytes_mut();

    bytes[0] = 0xF0;
    bytes[1] = 0x9F;
    bytes[2] = 0x8D;
    bytes[3] = 0x94;
}

assert_eq!("🍔∈🌏", s);

pub 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.

The caller must ensure that the returned pointer is never written to. If you need to mutate the contents of the string slice, use as_mut_ptr.

Examples

let s = "Hello";
let ptr = s.as_ptr();

pub fn as_mut_ptr(&mut self) -> *mut u8

Converts a mutable 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.

It is your responsibility to make sure that the string slice only gets modified in a way that it remains valid UTF-8.

pub fn get<I>(&self, i: I) -> Option<&<I as SliceIndex<str>>::Output>

where I: SliceIndex<str>,

Returns a subslice of str.

This is the non-panicking alternative to indexing the str. Returns None whenever equivalent indexing operation would panic.

Examples

let v = String::from("🗻∈🌏");

assert_eq!(Some("🗻"), v.get(0..4));

// indices not on UTF-8 sequence boundaries
assert!(v.get(1..).is_none());
assert!(v.get(..8).is_none());

// out of bounds
assert!(v.get(..42).is_none());

pub fn get_mut<I>( &mut self, i: I, ) -> Option<&mut <I as SliceIndex<str>>::Output>

where I: SliceIndex<str>,

Returns a mutable subslice of str.

This is the non-panicking alternative to indexing the str. Returns None whenever equivalent indexing operation would panic.

Examples

let mut v = String::from("hello");
// correct length
assert!(v.get_mut(0..5).is_some());
// out of bounds
assert!(v.get_mut(..42).is_none());
assert_eq!(Some("he"), v.get_mut(0..2).map(|v| &*v));

assert_eq!("hello", v);
{
    let s = v.get_mut(0..2);
    let s = s.map(|s| {
        s.make_ascii_uppercase();
        &*s
    });
    assert_eq!(Some("HE"), s);
}
assert_eq!("HEllo", v);

pub unsafe fn get_unchecked<I>(&self, i: I) -> &<I as SliceIndex<str>>::Output

where I: SliceIndex<str>,

Returns an unchecked subslice of str.

This is the unchecked alternative to indexing the str.

Safety

Callers of this function are responsible that these preconditions are satisfied:

• The starting index must not exceed the ending index;
• Indexes must be within bounds of the original slice;
• Indexes must lie on UTF-8 sequence boundaries.

Failing that, the returned string slice may reference invalid memory or violate the invariants communicated by the str type.

Examples

let v = "🗻∈🌏";
unsafe {
    assert_eq!("🗻", v.get_unchecked(0..4));
    assert_eq!("∈", v.get_unchecked(4..7));
    assert_eq!("🌏", v.get_unchecked(7..11));
}

pub unsafe fn get_unchecked_mut<I>( &mut self, i: I, ) -> &mut <I as SliceIndex<str>>::Output

where I: SliceIndex<str>,

Returns a mutable, unchecked subslice of str.

This is the unchecked alternative to indexing the str.

Safety

Callers of this function are responsible that these preconditions are satisfied:

• The starting index must not exceed the ending index;
• Indexes must be within bounds of the original slice;
• Indexes must lie on UTF-8 sequence boundaries.

Failing that, the returned string slice may reference invalid memory or violate the invariants communicated by the str type.

Examples

let mut v = String::from("🗻∈🌏");
unsafe {
    assert_eq!("🗻", v.get_unchecked_mut(0..4));
    assert_eq!("∈", v.get_unchecked_mut(4..7));
    assert_eq!("🌏", v.get_unchecked_mut(7..11));
}

pub unsafe fn slice_unchecked(&self, begin: usize, end: usize) -> &str

👎Deprecated since 1.29.0: use get_unchecked(begin..end) instead

Creates a string slice from another string slice, bypassing safety checks.

This is generally not recommended, use with caution! For a safe alternative see str and Index.

This new slice goes from begin to end, including begin but excluding end.

To get a mutable string slice instead, see the slice_mut_unchecked method.

Safety

Callers of this function are responsible that three preconditions are satisfied:

• begin must not exceed end.
• begin and end must be byte positions within the string slice.
• begin and end must lie on UTF-8 sequence boundaries.

Examples

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));
}

pub unsafe fn slice_mut_unchecked( &mut self, begin: usize, end: usize, ) -> &mut str

👎Deprecated since 1.29.0: use get_unchecked_mut(begin..end) instead

Creates a string slice from another string slice, bypassing safety checks.

This is generally not recommended, use with caution! For a safe alternative see str and IndexMut.

This new slice goes from begin to end, including begin but excluding end.

To get an immutable string slice instead, see the slice_unchecked method.

Safety

Callers of this function are responsible that three preconditions are satisfied:

• begin must not exceed end.
• begin and end must be byte positions within the string slice.
• begin and end must lie on UTF-8 sequence boundaries.

pub fn split_at(&self, mid: usize) -> (&str, &str)

Divides 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 past the end of the last code point of the string slice. For a non-panicking alternative see split_at_checked.

Examples

let s = "Per Martin-Löf";

let (first, last) = s.split_at(3);

assert_eq!("Per", first);
assert_eq!(" Martin-Löf", last);

pub fn split_at_mut(&mut self, mid: usize) -> (&mut str, &mut str)

Divides 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 past the end of the last code point of the string slice. For a non-panicking alternative see split_at_mut_checked.

Examples

let mut s = "Per Martin-Löf".to_string();
{
    let (first, last) = s.split_at_mut(3);
    first.make_ascii_uppercase();
    assert_eq!("PER", first);
    assert_eq!(" Martin-Löf", last);
}
assert_eq!("PER Martin-Löf", s);

pub fn split_at_checked(&self, mid: usize) -> Option<(&str, &str)>

Divides one string slice into two at an index.

The argument, mid, should be a valid byte offset from the start of the string. It must also be on the boundary of a UTF-8 code point. The method returns None if that’s not the case.

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_checked method.

Examples

let s = "Per Martin-Löf";

let (first, last) = s.split_at_checked(3).unwrap();
assert_eq!("Per", first);
assert_eq!(" Martin-Löf", last);

assert_eq!(None, s.split_at_checked(13));  // Inside “ö”
assert_eq!(None, s.split_at_checked(16));  // Beyond the string length

pub fn split_at_mut_checked( &mut self, mid: usize, ) -> Option<(&mut str, &mut str)>

Divides one mutable string slice into two at an index.

The argument, mid, should be a valid byte offset from the start of the string. It must also be on the boundary of a UTF-8 code point. The method returns None if that’s not the case.

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_checked method.

Examples

let mut s = "Per Martin-Löf".to_string();
if let Some((first, last)) = s.split_at_mut_checked(3) {
    first.make_ascii_uppercase();
    assert_eq!("PER", first);
    assert_eq!(" Martin-Löf", last);
}
assert_eq!("PER Martin-Löf", s);

assert_eq!(None, s.split_at_mut_checked(13));  // Inside “ö”
assert_eq!(None, s.split_at_mut_checked(16));  // Beyond the string length

pub 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 might not match your idea of what a ‘character’ is. Iteration over grapheme clusters may be what you actually want. This functionality is not provided by Rust’s standard library, check crates.io instead.

Examples

Basic usage:

let word = "goodbye";

let count = word.chars().count();
assert_eq!(7, count);

let mut chars = word.chars();

assert_eq!(Some('g'), chars.next());
assert_eq!(Some('o'), chars.next());
assert_eq!(Some('o'), chars.next());
assert_eq!(Some('d'), chars.next());
assert_eq!(Some('b'), chars.next());
assert_eq!(Some('y'), chars.next());
assert_eq!(Some('e'), chars.next());

assert_eq!(None, chars.next());

Remember, chars might not match your 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());

pub 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:

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 might not match your intuition about characters:

let yes = "y̆es";

let mut char_indices = yes.char_indices();

assert_eq!(Some((0, 'y')), char_indices.next()); // not (0, 'y̆')
assert_eq!(Some((1, '\u{0306}')), char_indices.next());

// note the 3 here - the previous character took up two bytes
assert_eq!(Some((3, 'e')), char_indices.next());
assert_eq!(Some((4, 's')), char_indices.next());

assert_eq!(None, char_indices.next());

pub fn bytes(&self) -> Bytes<'_>

Returns 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

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());

pub fn split_whitespace(&self) -> SplitWhitespace<'_>

Splits 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. If you only want to split on ASCII whitespace instead, use split_ascii_whitespace.

Examples

Basic usage:

let mut iter = "A few words".split_whitespace();

assert_eq!(Some("A"), iter.next());
assert_eq!(Some("few"), iter.next());
assert_eq!(Some("words"), iter.next());

assert_eq!(None, iter.next());

All kinds of whitespace are considered:

let mut iter = " Mary   had\ta\u{2009}little  \n\t lamb".split_whitespace();
assert_eq!(Some("Mary"), iter.next());
assert_eq!(Some("had"), iter.next());
assert_eq!(Some("a"), iter.next());
assert_eq!(Some("little"), iter.next());
assert_eq!(Some("lamb"), iter.next());

assert_eq!(None, iter.next());

If the string is empty or all whitespace, the iterator yields no string slices:

assert_eq!("".split_whitespace().next(), None);
assert_eq!("   ".split_whitespace().next(), None);

pub fn split_ascii_whitespace(&self) -> SplitAsciiWhitespace<'_>

Splits a string slice by ASCII whitespace.

The iterator returned will return string slices that are sub-slices of the original string slice, separated by any amount of ASCII whitespace.

To split by Unicode Whitespace instead, use split_whitespace.

Examples

Basic usage:

let mut iter = "A few words".split_ascii_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 ASCII whitespace are considered:

let mut iter = " Mary   had\ta little  \n\t lamb".split_ascii_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());

If the string is empty or all ASCII whitespace, the iterator yields no string slices:

assert_eq!("".split_ascii_whitespace().next(), None);
assert_eq!("   ".split_ascii_whitespace().next(), None);

pub fn lines(&self) -> Lines<'_>

Returns an iterator over the lines of a string, as string slices.

Lines are split at line endings that are either newlines (\n) or sequences of a carriage return followed by a line feed (\r\n).

Line terminators are not included in the lines returned by the iterator.

Note that any carriage return (\r) not immediately followed by a line feed (\n) does not split a line. These carriage returns are thereby included in the produced lines.

The final line ending is optional. A string that ends with a final line ending will return the same lines as an otherwise identical string without a final line ending.

Examples

Basic usage:

let text = "foo\r\nbar\n\nbaz\r";
let mut lines = text.lines();

assert_eq!(Some("foo"), lines.next());
assert_eq!(Some("bar"), lines.next());
assert_eq!(Some(""), lines.next());
// Trailing carriage return is included in the last line
assert_eq!(Some("baz\r"), lines.next());

assert_eq!(None, lines.next());

The final line does not require any ending:

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());

pub fn lines_any(&self) -> LinesAny<'_>

👎Deprecated since 1.4.0: use lines() instead now

Returns an iterator over the lines of a string.

pub fn encode_utf16(&self) -> EncodeUtf16<'_>

Returns an iterator of u16 over the string encoded as UTF-16.

Examples

let text = "Zażółć gęślą jaźń";

let utf8_len = text.len();
let utf16_len = text.encode_utf16().count();

assert!(utf16_len <= utf8_len);

pub fn contains<P>(&self, pat: P) -> bool

where P: Pattern,

Returns true if the given pattern matches a sub-slice of this string slice.

Returns false if it does not.

The pattern can be a &str, char, a slice of chars, or a function or closure that determines if a character matches.

Examples

let bananas = "bananas";

assert!(bananas.contains("nana"));
assert!(!bananas.contains("apples"));

pub fn starts_with<P>(&self, pat: P) -> bool

where P: Pattern,

Returns true if the given pattern matches a prefix of this string slice.

Returns false if it does not.

The pattern can be a &str, in which case this function will return true if the &str is a prefix of this string slice.

The pattern can also be a char, a slice of chars, or a function or closure that determines if a character matches. These will only be checked against the first character of this string slice. Look at the second example below regarding behavior for slices of chars.

Examples

let bananas = "bananas";

assert!(bananas.starts_with("bana"));
assert!(!bananas.starts_with("nana"));

let bananas = "bananas";

// Note that both of these assert successfully.
assert!(bananas.starts_with(&['b', 'a', 'n', 'a']));
assert!(bananas.starts_with(&['a', 'b', 'c', 'd']));

pub fn ends_with<P>(&self, pat: P) -> bool

where P: Pattern, <P as Pattern>::Searcher<'a>: for<'a> ReverseSearcher<'a>,

Returns true if the given pattern matches a suffix of this string slice.

Returns false if it does not.

The pattern can be a &str, char, a slice of chars, or a function or closure that determines if a character matches.

Examples

let bananas = "bananas";

assert!(bananas.ends_with("anas"));
assert!(!bananas.ends_with("nana"));

pub fn find<P>(&self, pat: P) -> Option<usize>

where P: Pattern,

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, a slice of chars, or a function or closure that determines if a character matches.

Examples

Simple patterns:

let s = "Löwe 老虎 Léopard Gepardi";

assert_eq!(s.find('L'), Some(0));
assert_eq!(s.find('é'), Some(14));
assert_eq!(s.find("pard"), Some(17));

More complex patterns using point-free style and closures:

let s = "Löwe 老虎 Léopard";

assert_eq!(s.find(char::is_whitespace), Some(5));
assert_eq!(s.find(char::is_lowercase), Some(1));
assert_eq!(s.find(|c: char| c.is_whitespace() || c.is_lowercase()), Some(1));
assert_eq!(s.find(|c: char| (c < 'o') && (c > 'a')), Some(4));

Not finding the pattern:

let s = "Löwe 老虎 Léopard";
let x: &[_] = &['1', '2'];

assert_eq!(s.find(x), None);

pub fn rfind<P>(&self, pat: P) -> Option<usize>

where P: Pattern, <P as Pattern>::Searcher<'a>: for<'a> ReverseSearcher<'a>,

Returns the byte index for the first character of the last match of the pattern in this string slice.

Returns None if the pattern doesn’t match.

The pattern can be a &str, char, a slice of chars, or a function or closure that determines if a character matches.

Examples

Simple patterns:

let s = "Löwe 老虎 Léopard Gepardi";

assert_eq!(s.rfind('L'), Some(13));
assert_eq!(s.rfind('é'), Some(14));
assert_eq!(s.rfind("pard"), Some(24));

More complex patterns with closures:

let s = "Löwe 老虎 Léopard";

assert_eq!(s.rfind(char::is_whitespace), Some(12));
assert_eq!(s.rfind(char::is_lowercase), Some(20));

Not finding the pattern:

let s = "Löwe 老虎 Léopard";
let x: &[_] = &['1', '2'];

assert_eq!(s.rfind(x), None);

pub fn split<P>(&self, pat: P) -> Split<'_, P>

where P: Pattern,

Returns an iterator over substrings of this string slice, separated by characters matched by a pattern.

The pattern can be a &str, char, a slice of chars, or a function or 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, e.g., char, but not for &str.

If the pattern allows a reverse search but its results might differ from a forward search, the rsplit method can be used.

Examples

Simple patterns:

let v: Vec<&str> = "Mary had a little lamb".split(' ').collect();
assert_eq!(v, ["Mary", "had", "a", "little", "lamb"]);

let v: Vec<&str> = "".split('X').collect();
assert_eq!(v, [""]);

let v: Vec<&str> = "lionXXtigerXleopard".split('X').collect();
assert_eq!(v, ["lion", "", "tiger", "leopard"]);

let v: Vec<&str> = "lion::tiger::leopard".split("::").collect();
assert_eq!(v, ["lion", "tiger", "leopard"]);

let v: Vec<&str> = "abc1def2ghi".split(char::is_numeric).collect();
assert_eq!(v, ["abc", "def", "ghi"]);

let v: Vec<&str> = "lionXtigerXleopard".split(char::is_uppercase).collect();
assert_eq!(v, ["lion", "tiger", "leopard"]);

If the pattern is a slice of chars, split on each occurrence of any of the characters:

let v: Vec<&str> = "2020-11-03 23:59".split(&['-', ' ', ':', '@'][..]).collect();
assert_eq!(v, ["2020", "11", "03", "23", "59"]);

A more complex pattern, using a closure:

let v: Vec<&str> = "abc1defXghi".split(|c| c == '1' || c == 'X').collect();
assert_eq!(v, ["abc", "def", "ghi"]);

If a string contains multiple contiguous separators, you will end up with empty strings in the output:

let x = "||||a||b|c".to_string();
let d: Vec<_> = x.split('|').collect();

assert_eq!(d, &["", "", "", "", "a", "", "b", "c"]);

Contiguous separators are separated by the empty string.

let x = "(///)".to_string();
let d: Vec<_> = x.split('/').collect();

assert_eq!(d, &["(", "", "", ")"]);

Separators at the start or end of a string are neighbored by empty strings.

let d: Vec<_> = "010".split("0").collect();
assert_eq!(d, &["", "1", ""]);

When the empty string is used as a separator, it separates every character in the string, along with the beginning and end of the string.

let f: Vec<_> = "rust".split("").collect();
assert_eq!(f, &["", "r", "u", "s", "t", ""]);

Contiguous separators can lead to possibly surprising behavior when whitespace is used as the separator. This code is correct:

let x = "    a  b c".to_string();
let d: Vec<_> = x.split(' ').collect();

assert_eq!(d, &["", "", "", "", "a", "", "b", "c"]);

It does not give you:

assert_eq!(d, &["a", "b", "c"]);

Use split_whitespace for this behavior.

pub fn split_inclusive<P>(&self, pat: P) -> SplitInclusive<'_, P>

where P: Pattern,

Returns an iterator over substrings of this string slice, separated by characters matched by a pattern.

Differs from the iterator produced by split in that split_inclusive leaves the matched part as the terminator of the substring.

The pattern can be a &str, char, a slice of chars, or a function or closure that determines if a character matches.

Examples

let v: Vec<&str> = "Mary had a little lamb\nlittle lamb\nlittle lamb."
    .split_inclusive('\n').collect();
assert_eq!(v, ["Mary had a little lamb\n", "little lamb\n", "little lamb."]);

If the last element of the string is matched, that element will be considered the terminator of the preceding substring. That substring will be the last item returned by the iterator.

let v: Vec<&str> = "Mary had a little lamb\nlittle lamb\nlittle lamb.\n"
    .split_inclusive('\n').collect();
assert_eq!(v, ["Mary had a little lamb\n", "little lamb\n", "little lamb.\n"]);

pub fn rsplit<P>(&self, pat: P) -> RSplit<'_, P>

where P: Pattern, <P as Pattern>::Searcher<'a>: for<'a> ReverseSearcher<'a>,

Returns 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, a slice of chars, or a function or 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 split method can be used.

Examples

Simple patterns:

let v: Vec<&str> = "Mary had a little lamb".rsplit(' ').collect();
assert_eq!(v, ["lamb", "little", "a", "had", "Mary"]);

let v: Vec<&str> = "".rsplit('X').collect();
assert_eq!(v, [""]);

let v: Vec<&str> = "lionXXtigerXleopard".rsplit('X').collect();
assert_eq!(v, ["leopard", "tiger", "", "lion"]);

let v: Vec<&str> = "lion::tiger::leopard".rsplit("::").collect();
assert_eq!(v, ["leopard", "tiger", "lion"]);

A more complex pattern, using a closure:

let v: Vec<&str> = "abc1defXghi".rsplit(|c| c == '1' || c == 'X').collect();
assert_eq!(v, ["ghi", "def", "abc"]);

pub fn split_terminator<P>(&self, pat: P) -> SplitTerminator<'_, P>

where P: Pattern,

Returns an iterator over substrings of the given string slice, separated by characters matched by a pattern.

The pattern can be a &str, char, a slice of chars, or a function or closure that determines if a character matches.

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, e.g., 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

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:C.D".split_terminator(&['.', ':'][..]).collect();
assert_eq!(v, ["A", "B", "C", "D"]);

pub fn rsplit_terminator<P>(&self, pat: P) -> RSplitTerminator<'_, P>

where P: Pattern, <P as Pattern>::Searcher<'a>: for<'a> ReverseSearcher<'a>,

Returns an iterator over substrings of self, separated by characters matched by a pattern and yielded in reverse order.

The pattern can be a &str, char, a slice of chars, or a function or closure that determines if a character matches.

Equivalent to split, except that the trailing substring is skipped if empty.

This method can be used for string data that is terminated, rather than separated by a pattern.

Iterator behavior

The returned iterator requires that the pattern supports a reverse search, and it will be double ended if a forward/reverse search yields the same elements.

For iterating from the front, the split_terminator method can be used.

Examples

let v: Vec<&str> = "A.B.".rsplit_terminator('.').collect();
assert_eq!(v, ["B", "A"]);

let v: Vec<&str> = "A..B..".rsplit_terminator(".").collect();
assert_eq!(v, ["", "B", "", "A"]);

let v: Vec<&str> = "A.B:C.D".rsplit_terminator(&['.', ':'][..]).collect();
assert_eq!(v, ["D", "C", "B", "A"]);

pub fn splitn<P>(&self, n: usize, pat: P) -> SplitN<'_, P>

where P: Pattern,

Returns an iterator over substrings of the given string slice, separated by a pattern, restricted to returning at most n items.

If n substrings are returned, the last substring (the nth substring) will contain the remainder of the string.

The pattern can be a &str, char, a slice of chars, or a function or closure that determines if a character matches.

Iterator behavior

The returned iterator will not be double ended, because it is not efficient to support.

If the pattern allows a reverse search, the rsplitn method can be used.

Examples

Simple patterns:

let v: Vec<&str> = "Mary had a little lambda".splitn(3, ' ').collect();
assert_eq!(v, ["Mary", "had", "a little lambda"]);

let v: Vec<&str> = "lionXXtigerXleopard".splitn(3, "X").collect();
assert_eq!(v, ["lion", "", "tigerXleopard"]);

let v: Vec<&str> = "abcXdef".splitn(1, 'X').collect();
assert_eq!(v, ["abcXdef"]);

let v: Vec<&str> = "".splitn(1, 'X').collect();
assert_eq!(v, [""]);

A more complex pattern, using a closure:

let v: Vec<&str> = "abc1defXghi".splitn(2, |c| c == '1' || c == 'X').collect();
assert_eq!(v, ["abc", "defXghi"]);

pub fn rsplitn<P>(&self, n: usize, pat: P) -> RSplitN<'_, P>

where P: Pattern, <P as Pattern>::Searcher<'a>: for<'a> ReverseSearcher<'a>,

Returns an iterator over substrings of this string slice, separated by a pattern, starting from the end of the string, restricted to returning at most n items.

If n substrings are returned, the last substring (the nth substring) will contain the remainder of the string.

The pattern can be a &str, char, a slice of chars, or a function or closure that determines if a character matches.

Iterator behavior

The returned iterator will not be double ended, because it is not efficient to support.

For splitting from the front, the splitn method can be used.

Examples

Simple patterns:

let v: Vec<&str> = "Mary had a little lamb".rsplitn(3, ' ').collect();
assert_eq!(v, ["lamb", "little", "Mary had a"]);

let v: Vec<&str> = "lionXXtigerXleopard".rsplitn(3, 'X').collect();
assert_eq!(v, ["leopard", "tiger", "lionX"]);

let v: Vec<&str> = "lion::tiger::leopard".rsplitn(2, "::").collect();
assert_eq!(v, ["leopard", "lion::tiger"]);

A more complex pattern, using a closure:

let v: Vec<&str> = "abc1defXghi".rsplitn(2, |c| c == '1' || c == 'X').collect();
assert_eq!(v, ["ghi", "abc1def"]);

pub fn split_once<P>(&self, delimiter: P) -> Option<(&str, &str)>

where P: Pattern,

Splits the string on the first occurrence of the specified delimiter and returns prefix before delimiter and suffix after delimiter.

Examples

assert_eq!("cfg".split_once('='), None);
assert_eq!("cfg=".split_once('='), Some(("cfg", "")));
assert_eq!("cfg=foo".split_once('='), Some(("cfg", "foo")));
assert_eq!("cfg=foo=bar".split_once('='), Some(("cfg", "foo=bar")));

pub fn rsplit_once<P>(&self, delimiter: P) -> Option<(&str, &str)>

where P: Pattern, <P as Pattern>::Searcher<'a>: for<'a> ReverseSearcher<'a>,

Splits the string on the last occurrence of the specified delimiter and returns prefix before delimiter and suffix after delimiter.

Examples

assert_eq!("cfg".rsplit_once('='), None);
assert_eq!("cfg=foo".rsplit_once('='), Some(("cfg", "foo")));
assert_eq!("cfg=foo=bar".rsplit_once('='), Some(("cfg=foo", "bar")));

pub fn matches<P>(&self, pat: P) -> Matches<'_, P>

where P: Pattern,

Returns an iterator over the disjoint matches of a pattern within the given string slice.

The pattern can be a &str, char, a slice of chars, or a function or 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, e.g., 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

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"]);

pub fn rmatches<P>(&self, pat: P) -> RMatches<'_, P>

where P: Pattern, <P as Pattern>::Searcher<'a>: for<'a> ReverseSearcher<'a>,

Returns an iterator over the disjoint matches of a pattern within this string slice, yielded in reverse order.

The pattern can be a &str, char, a slice of chars, or a function or 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

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"]);

pub fn match_indices<P>(&self, pat: P) -> MatchIndices<'_, P>

where P: Pattern,

Returns 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, a slice of chars, or a function or 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, e.g., 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

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`

pub fn rmatch_indices<P>(&self, pat: P) -> RMatchIndices<'_, P>

where P: Pattern, <P as Pattern>::Searcher<'a>: for<'a> ReverseSearcher<'a>,

Returns 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, a slice of chars, or a function or 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

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`

pub 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, which includes newlines.

Examples

let s = "\n Hello\tworld\t\n";

assert_eq!("Hello\tworld", s.trim());

pub fn trim_start(&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, which includes newlines.

Text directionality

A string is a sequence of bytes. start in this context means the first position of that byte string; for a left-to-right language like English or Russian, this will be left side, and for right-to-left languages like Arabic or Hebrew, this will be the right side.

Examples

Basic usage:

let s = "\n Hello\tworld\t\n";
assert_eq!("Hello\tworld\t\n", s.trim_start());

Directionality:

let s = "  English  ";
assert!(Some('E') == s.trim_start().chars().next());

let s = "  עברית  ";
assert!(Some('ע') == s.trim_start().chars().next());

pub fn trim_end(&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, which includes newlines.

Text directionality

A string is a sequence of bytes. end in this context means the last position of that byte string; for a left-to-right language like English or Russian, this will be right side, and for right-to-left languages like Arabic or Hebrew, this will be the left side.

Examples

Basic usage:

let s = "\n Hello\tworld\t\n";
assert_eq!("\n Hello\tworld", s.trim_end());

Directionality:

let s = "  English  ";
assert!(Some('h') == s.trim_end().chars().rev().next());

let s = "  עברית  ";
assert!(Some('ת') == s.trim_end().chars().rev().next());

pub fn trim_left(&self) -> &str

👎Deprecated since 1.33.0: superseded by trim_start

Returns a string slice with leading whitespace removed.

‘Whitespace’ is defined according to the terms of the Unicode Derived Core Property White_Space.

Text directionality

A string is a sequence of bytes. ‘Left’ in this context means the first position of that byte string; for a language like Arabic or Hebrew which are ‘right to left’ rather than ‘left to right’, this will be the right side, not the left.

Examples

Basic usage:

let s = " Hello\tworld\t";

assert_eq!("Hello\tworld\t", s.trim_left());

Directionality:

let s = "  English";
assert!(Some('E') == s.trim_left().chars().next());

let s = "  עברית";
assert!(Some('ע') == s.trim_left().chars().next());

pub fn trim_right(&self) -> &str

👎Deprecated since 1.33.0: superseded by trim_end

Returns a string slice with trailing whitespace removed.

‘Whitespace’ is defined according to the terms of the Unicode Derived Core Property White_Space.

Text directionality

A string is a sequence of bytes. ‘Right’ in this context means the last position of that byte string; for a language like Arabic or Hebrew which are ‘right to left’ rather than ‘left to right’, this will be the left side, not the right.

Examples

Basic usage:

let s = " Hello\tworld\t";

assert_eq!(" Hello\tworld", s.trim_right());

Directionality:

let s = "English  ";
assert!(Some('h') == s.trim_right().chars().rev().next());

let s = "עברית  ";
assert!(Some('ת') == s.trim_right().chars().rev().next());

pub fn trim_matches<P>(&self, pat: P) -> &str

where P: Pattern, <P as Pattern>::Searcher<'a>: for<'a> DoubleEndedSearcher<'a>,

Returns a string slice with all prefixes and suffixes that match a pattern repeatedly removed.

The pattern can be a char, a slice of chars, or a function or closure that determines if a character matches.

Examples

Simple patterns:

assert_eq!("11foo1bar11".trim_matches('1'), "foo1bar");
assert_eq!("123foo1bar123".trim_matches(char::is_numeric), "foo1bar");

let x: &[_] = &['1', '2'];
assert_eq!("12foo1bar12".trim_matches(x), "foo1bar");

A more complex pattern, using a closure:

assert_eq!("1foo1barXX".trim_matches(|c| c == '1' || c == 'X'), "foo1bar");

pub fn trim_start_matches<P>(&self, pat: P) -> &str

where P: Pattern,

Returns a string slice with all prefixes that match a pattern repeatedly removed.

The pattern can be a &str, char, a slice of chars, or a function or closure that determines if a character matches.

Text directionality

A string is a sequence of bytes. start in this context means the first position of that byte string; for a left-to-right language like English or Russian, this will be left side, and for right-to-left languages like Arabic or Hebrew, this will be the right side.

Examples

assert_eq!("11foo1bar11".trim_start_matches('1'), "foo1bar11");
assert_eq!("123foo1bar123".trim_start_matches(char::is_numeric), "foo1bar123");

let x: &[_] = &['1', '2'];
assert_eq!("12foo1bar12".trim_start_matches(x), "foo1bar12");

pub fn strip_prefix<P>(&self, prefix: P) -> Option<&str>

where P: Pattern,

Returns a string slice with the prefix removed.

If the string starts with the pattern prefix, returns the substring after the prefix, wrapped in Some. Unlike trim_start_matches, this method removes the prefix exactly once.

If the string does not start with prefix, returns None.

The pattern can be a &str, char, a slice of chars, or a function or closure that determines if a character matches.

Examples

assert_eq!("foo:bar".strip_prefix("foo:"), Some("bar"));
assert_eq!("foo:bar".strip_prefix("bar"), None);
assert_eq!("foofoo".strip_prefix("foo"), Some("foo"));

pub fn strip_suffix<P>(&self, suffix: P) -> Option<&str>

where P: Pattern, <P as Pattern>::Searcher<'a>: for<'a> ReverseSearcher<'a>,

Returns a string slice with the suffix removed.

If the string ends with the pattern suffix, returns the substring before the suffix, wrapped in Some. Unlike trim_end_matches, this method removes the suffix exactly once.

If the string does not end with suffix, returns None.

The pattern can be a &str, char, a slice of chars, or a function or closure that determines if a character matches.

Examples

assert_eq!("bar:foo".strip_suffix(":foo"), Some("bar"));
assert_eq!("bar:foo".strip_suffix("bar"), None);
assert_eq!("foofoo".strip_suffix("foo"), Some("foo"));

pub fn trim_end_matches<P>(&self, pat: P) -> &str

where P: Pattern, <P as Pattern>::Searcher<'a>: for<'a> ReverseSearcher<'a>,

Returns a string slice with all suffixes that match a pattern repeatedly removed.

The pattern can be a &str, char, a slice of chars, or a function or closure that determines if a character matches.

Text directionality

A string is a sequence of bytes. end in this context means the last position of that byte string; for a left-to-right language like English or Russian, this will be right side, and for right-to-left languages like Arabic or Hebrew, this will be the left side.

Examples

Simple patterns:

assert_eq!("11foo1bar11".trim_end_matches('1'), "11foo1bar");
assert_eq!("123foo1bar123".trim_end_matches(char::is_numeric), "123foo1bar");

let x: &[_] = &['1', '2'];
assert_eq!("12foo1bar12".trim_end_matches(x), "12foo1bar");

A more complex pattern, using a closure:

assert_eq!("1fooX".trim_end_matches(|c| c == '1' || c == 'X'), "1foo");

pub fn trim_left_matches<P>(&self, pat: P) -> &str

where P: Pattern,

👎Deprecated since 1.33.0: superseded by trim_start_matches

Returns a string slice with all prefixes that match a pattern repeatedly removed.

The pattern can be a &str, char, a slice of chars, or a function or 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

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");

pub fn trim_right_matches<P>(&self, pat: P) -> &str

where P: Pattern, <P as Pattern>::Searcher<'a>: for<'a> ReverseSearcher<'a>,

👎Deprecated since 1.33.0: superseded by trim_end_matches

Returns a string slice with all suffixes that match a pattern repeatedly removed.

The pattern can be a &str, char, a slice of chars, or a function or closure that determines if a character matches.

Text directionality

A string is a sequence of bytes. ‘Right’ in this context means the last position of that byte string; for a language like Arabic or Hebrew which are ‘right to left’ rather than ‘left to right’, this will be the left side, not the right.

Examples

Simple patterns:

assert_eq!("11foo1bar11".trim_right_matches('1'), "11foo1bar");
assert_eq!("123foo1bar123".trim_right_matches(char::is_numeric), "123foo1bar");

let x: &[_] = &['1', '2'];
assert_eq!("12foo1bar12".trim_right_matches(x), "12foo1bar");

A more complex pattern, using a closure:

assert_eq!("1fooX".trim_right_matches(|c| c == '1' || c == 'X'), "1foo");

pub fn parse<F>(&self) -> Result<F, <F as FromStr>::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 into 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.

Examples

Basic usage

let four: u32 = "4".parse().unwrap();

assert_eq!(4, four);

Using the ‘turbofish’ instead of annotating four:

let four = "4".parse::<u32>();

assert_eq!(Ok(4), four);

Failing to parse:

let nope = "j".parse::<u32>();

assert!(nope.is_err());

pub fn is_ascii(&self) -> bool

Checks if all characters in this string are within the ASCII range.

Examples

let ascii = "hello!\n";
let non_ascii = "Grüße, Jürgen ❤";

assert!(ascii.is_ascii());
assert!(!non_ascii.is_ascii());

pub fn as_ascii(&self) -> Option<&[AsciiChar]>

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

If this string slice is_ascii, returns it as a slice of ASCII characters, otherwise returns None.

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

Checks that two strings are an ASCII case-insensitive match.

Same as to_ascii_lowercase(a) == to_ascii_lowercase(b), but without allocating and copying temporaries.

Examples

assert!("Ferris".eq_ignore_ascii_case("FERRIS"));
assert!("Ferrös".eq_ignore_ascii_case("FERRöS"));
assert!(!"Ferrös".eq_ignore_ascii_case("FERRÖS"));

pub fn make_ascii_uppercase(&mut self)

Converts this string to its ASCII upper case equivalent in-place.

ASCII letters ‘a’ to ‘z’ are mapped to ‘A’ to ‘Z’, but non-ASCII letters are unchanged.

To return a new uppercased value without modifying the existing one, use to_ascii_uppercase().

Examples

let mut s = String::from("Grüße, Jürgen ❤");

s.make_ascii_uppercase();

assert_eq!("GRüßE, JüRGEN ❤", s);

pub fn make_ascii_lowercase(&mut self)

Converts this string to its ASCII lower case equivalent in-place.

ASCII letters ‘A’ to ‘Z’ are mapped to ‘a’ to ‘z’, but non-ASCII letters are unchanged.

To return a new lowercased value without modifying the existing one, use to_ascii_lowercase().

Examples

let mut s = String::from("GRÜßE, JÜRGEN ❤");

s.make_ascii_lowercase();

assert_eq!("grÜße, jÜrgen ❤", s);

pub fn trim_ascii_start(&self) -> &str

Returns a string slice with leading ASCII whitespace removed.

‘Whitespace’ refers to the definition used by u8::is_ascii_whitespace.

Examples

assert_eq!(" \t \u{3000}hello world\n".trim_ascii_start(), "\u{3000}hello world\n");
assert_eq!("  ".trim_ascii_start(), "");
assert_eq!("".trim_ascii_start(), "");

pub fn trim_ascii_end(&self) -> &str

Returns a string slice with trailing ASCII whitespace removed.

‘Whitespace’ refers to the definition used by u8::is_ascii_whitespace.

Examples

assert_eq!("\r hello world\u{3000}\n ".trim_ascii_end(), "\r hello world\u{3000}");
assert_eq!("  ".trim_ascii_end(), "");
assert_eq!("".trim_ascii_end(), "");

pub fn trim_ascii(&self) -> &str

Returns a string slice with leading and trailing ASCII whitespace removed.

‘Whitespace’ refers to the definition used by u8::is_ascii_whitespace.

Examples

assert_eq!("\r hello world\n ".trim_ascii(), "hello world");
assert_eq!("  ".trim_ascii(), "");
assert_eq!("".trim_ascii(), "");

pub fn escape_debug(&self) -> EscapeDebug<'_>

Returns an iterator that escapes each char in self with char::escape_debug.

Note: only extended grapheme codepoints that begin the string will be escaped.

Examples

As an iterator:

for c in "❤\n!".escape_debug() {
    print!("{c}");
}
println!();

Using println! directly:

println!("{}", "❤\n!".escape_debug());

Both are equivalent to:

println!("❤\\n!");

Using to_string:

assert_eq!("❤\n!".escape_debug().to_string(), "❤\\n!");

pub fn escape_default(&self) -> EscapeDefault<'_>

Returns an iterator that escapes each char in self with char::escape_default.

Examples

As an iterator:

for c in "❤\n!".escape_default() {
    print!("{c}");
}
println!();

Using println! directly:

println!("{}", "❤\n!".escape_default());

Both are equivalent to:

println!("\\u{{2764}}\\n!");

Using to_string:

assert_eq!("❤\n!".escape_default().to_string(), "\\u{2764}\\n!");

pub fn escape_unicode(&self) -> EscapeUnicode<'_>

Returns an iterator that escapes each char in self with char::escape_unicode.

Examples

As an iterator:

for c in "❤\n!".escape_unicode() {
    print!("{c}");
}
println!();

Using println! directly:

println!("{}", "❤\n!".escape_unicode());

Both are equivalent to:

println!("\\u{{2764}}\\u{{a}}\\u{{21}}");

Using to_string:

assert_eq!("❤\n!".escape_unicode().to_string(), "\\u{2764}\\u{a}\\u{21}");

pub fn substr_range(&self, substr: &str) -> Option<Range<usize>>

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

Returns the range that a substring points to.

Returns None if substr does not point within self.

Unlike str::find, this does not search through the string. Instead, it uses pointer arithmetic to find where in the string substr is derived from.

This is useful for extending str::split and similar methods.

Note that this method may return false positives (typically either Some(0..0) or Some(self.len()..self.len())) if substr is a zero-length str that points at the beginning or end of another, independent, str.

Examples

#![feature(substr_range)]

let data = "a, b, b, a";
let mut iter = data.split(", ").map(|s| data.substr_range(s).unwrap());

assert_eq!(iter.next(), Some(0..1));
assert_eq!(iter.next(), Some(3..4));
assert_eq!(iter.next(), Some(6..7));
assert_eq!(iter.next(), Some(9..10));

pub fn as_str(&self) -> &str

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

Returns the same string as a string slice &str.

This method is redundant when used directly on &str, but it helps dereferencing other string-like types to string slices, for example references to Box<str> or Arc<str>.

pub fn replace<P>(&self, from: P, to: &str) -> String

where P: Pattern,

Replaces all matches of a pattern with another string.

replace creates a new String, and copies the data from this string slice into it. While doing so, it attempts to find matches of a pattern. If it finds any, it replaces them with the replacement string slice.

Examples

Basic usage:

let s = "this is old";

assert_eq!("this is new", s.replace("old", "new"));
assert_eq!("than an old", s.replace("is", "an"));

When the pattern doesn’t match, it returns this string slice as String:

let s = "this is old";
assert_eq!(s, s.replace("cookie monster", "little lamb"));

pub fn replacen<P>(&self, pat: P, to: &str, count: usize) -> String

where P: Pattern,

Replaces first N matches of a pattern with another string.

replacen creates a new String, and copies the data from this string slice into it. While doing so, it attempts to find matches of a pattern. If it finds any, it replaces them with the replacement string slice at most count times.

Examples

Basic usage:

let s = "foo foo 123 foo";
assert_eq!("new new 123 foo", s.replacen("foo", "new", 2));
assert_eq!("faa fao 123 foo", s.replacen('o', "a", 3));
assert_eq!("foo foo new23 foo", s.replacen(char::is_numeric, "new", 1));

When the pattern doesn’t match, it returns this string slice as String:

let s = "this is old";
assert_eq!(s, s.replacen("cookie monster", "little lamb", 10));

pub 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.

Since some characters can expand into multiple characters when changing the case, this function returns a String instead of modifying the parameter in-place.

Examples

Basic usage:

let s = "HELLO";

assert_eq!("hello", s.to_lowercase());

A tricky example, with sigma:

let sigma = "Σ";

assert_eq!("σ", sigma.to_lowercase());

// but at the end of a word, it's ς, not σ:
let odysseus = "ὈΔΥΣΣΕΎΣ";

assert_eq!("ὀδυσσεύς", odysseus.to_lowercase());

Languages without case are not changed:

let new_year = "农历新年";

assert_eq!(new_year, new_year.to_lowercase());

pub 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.

Since some characters can expand into multiple characters when changing the case, this function returns a String instead of modifying the parameter in-place.

Examples

Basic usage:

let s = "hello";

assert_eq!("HELLO", s.to_uppercase());

Scripts without case are not changed:

let new_year = "农历新年";

assert_eq!(new_year, new_year.to_uppercase());

One character can become multiple:

let s = "tschüß";

assert_eq!("TSCHÜSS", s.to_uppercase());

pub fn repeat(&self, n: usize) -> String

Creates a new String by repeating a string n times.

Panics

This function will panic if the capacity would overflow.

Examples

Basic usage:

assert_eq!("abc".repeat(4), String::from("abcabcabcabc"));

A panic upon overflow:

// this will panic at runtime
let huge = "0123456789abcdef".repeat(usize::MAX);

pub fn to_ascii_uppercase(&self) -> String

Returns a copy of this string where each character is mapped to its ASCII upper case equivalent.

ASCII letters ‘a’ to ‘z’ are mapped to ‘A’ to ‘Z’, but non-ASCII letters are unchanged.

To uppercase the value in-place, use make_ascii_uppercase.

To uppercase ASCII characters in addition to non-ASCII characters, use to_uppercase.

Examples

let s = "Grüße, Jürgen ❤";

assert_eq!("GRüßE, JüRGEN ❤", s.to_ascii_uppercase());

pub fn to_ascii_lowercase(&self) -> String

Returns a copy of this string where each character is mapped to its ASCII lower case equivalent.

ASCII letters ‘A’ to ‘Z’ are mapped to ‘a’ to ‘z’, but non-ASCII letters are unchanged.

To lowercase the value in-place, use make_ascii_lowercase.

To lowercase ASCII characters in addition to non-ASCII characters, use to_lowercase.

Examples

let s = "Grüße, Jürgen ❤";

assert_eq!("grüße, jürgen ❤", s.to_ascii_lowercase());

Trait Implementations

impl Add<&str> for CompactString

type Output = CompactString

The resulting type after applying the + operator.

fn add(self, rhs: &str) -> <CompactString as Add<&str>>::Output

Performs the + operation.

impl AddAssign<&str> for CompactString

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

Performs the += operation.

impl AsRef<[u8]> for CompactString

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

Converts this type into a shared reference of the (usually inferred) input type.

impl AsRef<OsStr> for CompactString

fn as_ref(&self) -> &OsStr

Converts this type into a shared reference of the (usually inferred) input type.

impl AsRef<Path> for CompactString

fn as_ref(&self) -> &Path

Converts this type into a shared reference of the (usually inferred) input type.

impl AsRef<str> for CompactString

fn as_ref(&self) -> &str

Converts this type into a shared reference of the (usually inferred) input type.

impl Borrow<str> for CompactString

fn borrow(&self) -> &str

Immutably borrows from an owned value.

impl BorrowMut<str> for CompactString

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

Mutably borrows from an owned value.

impl Clone for CompactString

fn clone(&self) -> CompactString

Returns a copy of the value.

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

Performs copy-assignment from source.

impl Debug for CompactString

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

Formats the value using the given formatter.

impl Default for CompactString

fn default() -> CompactString

Returns the “default value” for a type.

impl Deref for CompactString

type Target = str

The resulting type after dereferencing.

fn deref(&self) -> &str

Dereferences the value.

impl DerefMut for CompactString

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

Mutably dereferences the value.

impl Display for CompactString

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

Formats the value using the given formatter.

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

fn extend<T>(&mut self, iter: T)

where T: IntoIterator<Item = &'a char>,

Extends a collection with the contents of an iterator.

fn extend_one(&mut self, item: A)

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

Extends a collection with exactly one element.

fn extend_reserve(&mut self, additional: usize)

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

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

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

fn extend<T>(&mut self, iter: T)

where T: IntoIterator<Item = &'a str>,

Extends a collection with the contents of an iterator.

fn extend_one(&mut self, item: A)

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

Extends a collection with exactly one element.

fn extend_reserve(&mut self, additional: usize)

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

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

impl Extend<Box<str>> for CompactString

fn extend<T>(&mut self, iter: T)

where T: IntoIterator<Item = Box<str>>,

Extends a collection with the contents of an iterator.

fn extend_one(&mut self, item: A)

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

Extends a collection with exactly one element.

fn extend_reserve(&mut self, additional: usize)

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

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

impl Extend<CompactString> for CompactString

fn extend<T>(&mut self, iter: T)

where T: IntoIterator<Item = CompactString>,

Extends a collection with the contents of an iterator.

fn extend_one(&mut self, item: A)

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

Extends a collection with exactly one element.

fn extend_reserve(&mut self, additional: usize)

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

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

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

fn extend<T>(&mut self, iter: T)

where T: IntoIterator<Item = CompactString>,

Extends a collection with the contents of an iterator.

fn extend_one(&mut self, item: A)

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

Extends a collection with exactly one element.

fn extend_reserve(&mut self, additional: usize)

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

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

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

fn extend<T>(&mut self, iter: T)

where T: IntoIterator<Item = Cow<'a, str>>,

Extends a collection with the contents of an iterator.

fn extend_one(&mut self, item: A)

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

Extends a collection with exactly one element.

fn extend_reserve(&mut self, additional: usize)

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

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

impl Extend<String> for CompactString

fn extend<T>(&mut self, iter: T)

where T: IntoIterator<Item = String>,

Extends a collection with the contents of an iterator.

fn extend_one(&mut self, item: A)

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

Extends a collection with exactly one element.

fn extend_reserve(&mut self, additional: usize)

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

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

impl Extend<char> for CompactString

fn extend<T>(&mut self, iter: T)

where T: IntoIterator<Item = char>,

Extends a collection with the contents of an iterator.

fn extend_one(&mut self, item: A)

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

Extends a collection with exactly one element.

fn extend_reserve(&mut self, additional: usize)

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

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

impl<'a> From<&'a CompactString> for Cow<'a, str>

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

Converts to this type from the input type.

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

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

Converts to this type from the input type.

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

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

Converts to this type from the input type.

impl From<Box<str>> for CompactString

fn from(b: Box<str>) -> CompactString

Converts to this type from the input type.

impl From<CompactString> for Arc<str>

fn from(value: CompactString) -> Arc<str>

Converts to this type from the input type.

impl From<CompactString> for Cow<'_, str>

fn from(s: CompactString) -> Cow<'_, str>

Converts to this type from the input type.

impl From<CompactString> for PathBuf

fn from(value: CompactString) -> PathBuf

Converts to this type from the input type.

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

fn from(cow: Cow<'a, str>) -> CompactString

Converts to this type from the input type.

impl From<String> for CompactString

fn from(s: String) -> CompactString

Converts to this type from the input type.

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

fn from_iter<T>(iter: T) -> CompactString

where T: IntoIterator<Item = &'a char>,

Creates a value from an iterator.

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

fn from_iter<T>(iter: T) -> CompactString

where T: IntoIterator<Item = &'a str>,

Creates a value from an iterator.

impl FromIterator<Box<str>> for CompactString

fn from_iter<T>(iter: T) -> CompactString

where T: IntoIterator<Item = Box<str>>,

Creates a value from an iterator.

impl FromIterator<CompactString> for CompactString

fn from_iter<T>(iter: T) -> CompactString

where T: IntoIterator<Item = CompactString>,

Creates a value from an iterator.

impl FromIterator<CompactString> for Cow<'_, str>

fn from_iter<T>(iter: T) -> Cow<'_, str>

where T: IntoIterator<Item = CompactString>,

Creates a value from an iterator.

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

fn from_iter<T>(iter: T) -> CompactString

where T: IntoIterator<Item = Cow<'a, str>>,

Creates a value from an iterator.

impl FromIterator<String> for CompactString

fn from_iter<T>(iter: T) -> CompactString

where T: IntoIterator<Item = String>,

Creates a value from an iterator.

impl