Enum collections::borrow::Cow

pub enum Cow<'a, B: ?Sized + 'a> where B: ToOwned {
    Borrowed(&'a B),
    Owned(B::Owned),
}

A clone-on-write smart pointer.

The type Cow is a smart pointer providing clone-on-write functionality: it can enclose and provide immutable access to borrowed data, and clone the data lazily when mutation or ownership is required. The type is designed to work with general borrowed data via the Borrow trait.

Cow implements Deref, which means that you can call non-mutating methods directly on the data it encloses. If mutation is desired, to_mut will obtain a mutable reference to an owned value, cloning if necessary.

Examples

fn main() { use std::borrow::Cow; #[allow(dead_code)] fn abs_all(input: &mut Cow<[i32]>) { for i in 0..input.len() { let v = input[i]; if v < 0 { // clones into a vector the first time (if not already owned) input.to_mut()[i] = -v; } } } }

use std::borrow::Cow;

fn abs_all(input: &mut Cow<[i32]>) {
    for i in 0..input.len() {
        let v = input[i];
        if v < 0 {
            // clones into a vector the first time (if not already owned)
            input.to_mut()[i] = -v;
        }
    }
}

Variants

Borrowed(&'a B)

Borrowed data.

Owned(B::Owned)

Owned data.

Methods

impl<'a, B: ?Sized> Cow<'a, B> where B: ToOwned

fn to_mut(&mut self) -> &mut B::Owned

Acquires a mutable reference to the owned form of the data.

Clones the data if it is not already owned.

Examples

fn main() { use std::borrow::Cow; let mut cow: Cow<[_]> = Cow::Owned(vec![1, 2, 3]); let hello = cow.to_mut(); assert_eq!(hello, &[1, 2, 3]); }

use std::borrow::Cow;

let mut cow: Cow<[_]> = Cow::Owned(vec![1, 2, 3]);

let hello = cow.to_mut();

assert_eq!(hello, &[1, 2, 3]);

fn into_owned(self) -> B::Owned

Extracts the owned data.

Clones the data if it is not already owned.

Examples

fn main() { use std::borrow::Cow; let cow: Cow<[_]> = Cow::Owned(vec![1, 2, 3]); let hello = cow.into_owned(); assert_eq!(vec![1, 2, 3], hello); }

use std::borrow::Cow;

let cow: Cow<[_]> = Cow::Owned(vec![1, 2, 3]);

let hello = cow.into_owned();

assert_eq!(vec![1, 2, 3], hello);

Trait Implementations

impl<'a, B: ?Sized> Borrow<B> for Cow<'a, B> where B: ToOwned, B::Owned: 'a

fn borrow(&self) -> &B

Immutably borrows from an owned value.

impl<'a, B: ?Sized> Clone for Cow<'a, B> where B: ToOwned

fn clone(&self) -> Cow<'a, B>

Returns a copy of the value.

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

Performs copy-assignment from source.

impl<'a, B: ?Sized> Deref for Cow<'a, B> where B: ToOwned

type Target = B

The resulting type after dereferencing

fn deref(&self) -> &B

The method called to dereference a value

impl<'a, B: ?Sized> Eq for Cow<'a, B> where B: Eq + ToOwned

impl<'a, B: ?Sized> Ord for Cow<'a, B> where B: Ord + ToOwned

fn cmp(&self, other: &Cow<'a, B>) -> Ordering

This method returns an Ordering between self and other.

impl<'a, 'b, B: ?Sized, C: ?Sized> PartialEq<Cow<'b, C>> for Cow<'a, B> where B: PartialEq<C> + ToOwned, C: ToOwned

fn eq(&self, other: &Cow<'b, C>) -> bool

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

fn ne(&self, other: &Rhs) -> bool

This method tests for !=.

impl<'a, B: ?Sized> PartialOrd for Cow<'a, B> where B: PartialOrd + ToOwned

fn partial_cmp(&self, other: &Cow<'a, B>) -> Option<Ordering>

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

fn lt(&self, other: &Rhs) -> bool

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

fn le(&self, other: &Rhs) -> bool

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

fn gt(&self, other: &Rhs) -> bool

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

fn ge(&self, other: &Rhs) -> bool

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

impl<'a, B: ?Sized> Debug for Cow<'a, B> where B: Debug + ToOwned, B::Owned: Debug

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

Formats the value using the given formatter.

impl<'a, B: ?Sized> Display for Cow<'a, B> where B: Display + ToOwned, B::Owned: Display

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

Formats the value using the given formatter.

impl<'a, B: ?Sized> Hash for Cow<'a, B> where B: Hash + ToOwned

fn hash<H: Hasher>(&self, state: &mut H)

Feeds this value into the state given, updating the hasher as necessary.

fn hash_slice<H>(data: &[Self], state: &mut H) where H: Hasher

Feeds a slice of this type into the state provided.

impl<'a, T: ?Sized + ToOwned> AsRef<T> for Cow<'a, T>

fn as_ref(&self) -> &T

Performs the conversion.

impl<'a, 'b> PartialEq<str> for Cow<'a, str>

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

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

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

This method tests for !=.

impl<'a, 'b> PartialEq<&'b str> for Cow<'a, str>

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

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

fn ne(&self, other: &&'b str) -> bool

This method tests for !=.

impl<'a, 'b> PartialEq<String> for Cow<'a, str>

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

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

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

This method tests for !=.

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

fn from(s: &'a str) -> Cow<'a, str>

Performs the conversion.

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

fn from(s: String) -> Cow<'a, str>

Performs the conversion.

impl<'a, 'b, A: Clone, B> PartialEq<&'b [B]> for Cow<'a, [A]> where A: PartialEq<B>

fn eq(&self, other: &&'b [B]) -> bool

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

fn ne(&self, other: &&'b [B]) -> bool

This method tests for !=.

impl<'a, 'b, A: Clone, B> PartialEq<&'b mut [B]> for Cow<'a, [A]> where A: PartialEq<B>

fn eq(&self, other: &&'b mut [B]) -> bool

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

fn ne(&self, other: &&'b mut [B]) -> bool

This method tests for !=.

impl<'a, 'b, A: Clone, B> PartialEq<Vec<B>> for Cow<'a, [A]> where A: PartialEq<B>

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

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

fn ne(&self, other: &Vec<B>) -> bool

This method tests for !=.

impl<'a, T: Clone> From<&'a [T]> for Cow<'a, [T]>

fn from(s: &'a [T]) -> Cow<'a, [T]>

Performs the conversion.

impl<'a, T: Clone> From<Vec<T>> for Cow<'a, [T]>

fn from(v: Vec<T>) -> Cow<'a, [T]>

Performs the conversion.

impl<'a, T> FromIterator<T> for Cow<'a, [T]> where T: Clone

fn from_iter<I: IntoIterator<Item=T>>(it: I) -> Cow<'a, [T]>

Creates a value from an iterator.