Enum std::borrow::Cow1.0.0 [] [src]

pub enum Cow<'a, B> where B: 'a + ToOwned + ?Sized {
    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

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 if not already owned.
            input.to_mut()[i] = -v;
        }
    }
}

// No clone occurs because `input` doesn't need to be mutated.
let slice = [0, 1, 2];
let mut input = Cow::from(&slice[..]);
abs_all(&mut input);

// Clone occurs because `input` needs to be mutated.
let slice = [-1, 0, 1];
let mut input = Cow::from(&slice[..]);
abs_all(&mut input);

// No clone occurs because `input` is already owned.
let mut input = Cow::from(vec![-1, 0, 1]);
abs_all(&mut input);Run

Variants

Borrowed data.

Owned data.

Methods

impl<'a, B> Cow<'a, B> where B: ToOwned + ?Sized
[src]

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

Clones the data if it is not already owned.

Examples

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]);Run

Extracts the owned data.

Clones the data if it is not already owned.

Examples

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);Run

Trait Implementations

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

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

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

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

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

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

impl<'a, B> Deref for Cow<'a, B> where B: ToOwned + ?Sized
[src]

The resulting type after dereferencing

The method called to dereference a value

impl<'a> FromIterator<char> for Cow<'a, str>
1.12.0
[src]

Creates a value from an iterator. Read more

impl<'a, 'b> FromIterator<&'b str> for Cow<'a, str>
1.12.0
[src]

Creates a value from an iterator. Read more

impl<'a> FromIterator<String> for Cow<'a, str>
1.12.0
[src]

Creates a value from an iterator. Read more

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

Creates a value from an iterator. Read more

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

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

Feeds a slice of this type into the state provided.

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

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

Formats the value using the given formatter.

impl<'a> From<&'a str> for Cow<'a, str>
[src]

Performs the conversion.

impl<'a> From<String> for Cow<'a, str>
[src]

Performs the conversion.

impl<'a, T> From<&'a [T]> for Cow<'a, [T]> where T: Clone
1.7.0
[src]

Performs the conversion.

impl<'a, T> From<Vec<T>> for Cow<'a, [T]> where T: Clone
1.7.0
[src]

Performs the conversion.

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

Formats the value using the given formatter.

impl<'a, T> AsRef<T> for Cow<'a, T> where T: ToOwned + ?Sized
[src]

Performs the conversion.

impl<'a, B> Default for Cow<'a, B> where B: ToOwned + ?Sized, B::Owned: Default
1.11.0
[src]

Creates an owned Cow<'a, B> with the default value for the contained owned value.

impl<'a, B> Clone for Cow<'a, B> where B: ToOwned + ?Sized
[src]

Returns a copy of the value. Read more

Performs copy-assignment from source. Read more

impl<'a> Add<&'a str> for Cow<'a, str>
1.14.0
[src]

The resulting type after applying the + operator

The method for the + operator

impl<'a> Add<Cow<'a, str>> for Cow<'a, str>
1.14.0
[src]

The resulting type after applying the + operator

The method for the + operator

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

This method returns an Ordering between self and other. Read more

impl<'a> AddAssign<&'a str> for Cow<'a, str>
1.14.0
[src]

The method for the += operator

impl<'a> AddAssign<Cow<'a, str>> for Cow<'a, str>
1.14.0
[src]

The method for the += operator

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

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

This method tests for !=.

impl<'a, 'b> PartialEq<str> for Cow<'a, str>
[src]

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

This method tests for !=.

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

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

This method tests for !=.

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

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

This method tests for !=.

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

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

This method tests for !=.

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

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

This method tests for !=.

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

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

This method tests for !=.

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

Immutably borrows from an owned value. Read more

impl<'a, 'b> PartialEq<OsStr> for Cow<'a, OsStr>
1.8.0
[src]

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

This method tests for !=.

impl<'a, 'b> PartialOrd<OsStr> for Cow<'a, OsStr>
1.8.0
[src]

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

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

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

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

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

impl<'a, 'b> PartialEq<&'b OsStr> for Cow<'a, OsStr>
1.8.0
[src]

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

This method tests for !=.

impl<'a, 'b> PartialOrd<&'b OsStr> for Cow<'a, OsStr>
1.8.0
[src]

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

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

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

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

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

impl<'a, 'b> PartialEq<OsString> for Cow<'a, OsStr>
1.8.0
[src]

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

This method tests for !=.

impl<'a, 'b> PartialOrd<OsString> for Cow<'a, OsStr>
1.8.0
[src]

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

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

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

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

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

impl<'a> From<&'a Path> for Cow<'a, Path>
1.6.0
[src]

Performs the conversion.

impl<'a> From<PathBuf> for Cow<'a, Path>
1.6.0
[src]

Performs the conversion.

impl<'a> AsRef<Path> for Cow<'a, OsStr>
1.8.0
[src]

Performs the conversion.

impl<'a, 'b> PartialEq<Path> for Cow<'a, Path>
1.6.0
[src]

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

This method tests for !=.

impl<'a, 'b> PartialOrd<Path> for Cow<'a, Path>
1.8.0
[src]

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

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

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

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

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

impl<'a, 'b> PartialEq<&'b Path> for Cow<'a, Path>
1.6.0
[src]

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

This method tests for !=.

impl<'a, 'b> PartialOrd<&'b Path> for Cow<'a, Path>
1.8.0
[src]

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

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

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

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

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

impl<'a, 'b> PartialEq<PathBuf> for Cow<'a, Path>
1.6.0
[src]

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

This method tests for !=.

impl<'a, 'b> PartialOrd<PathBuf> for Cow<'a, Path>
1.8.0
[src]

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

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

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

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

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

impl<'a, 'b> PartialEq<PathBuf> for Cow<'a, OsStr>
1.8.0
[src]

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

This method tests for !=.

impl<'a, 'b> PartialOrd<PathBuf> for Cow<'a, OsStr>
1.8.0
[src]

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

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

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

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

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

impl<'a, 'b> PartialEq<Path> for Cow<'a, OsStr>
1.8.0
[src]

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

This method tests for !=.

impl<'a, 'b> PartialOrd<Path> for Cow<'a, OsStr>
1.8.0
[src]

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

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

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

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

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

impl<'a, 'b> PartialEq<&'a Path> for Cow<'b, OsStr>
1.8.0
[src]

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

This method tests for !=.

impl<'a, 'b> PartialOrd<&'a Path> for Cow<'b, OsStr>
1.8.0
[src]

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

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

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

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

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

impl<'a, 'b> PartialEq<OsStr> for Cow<'a, Path>
1.8.0
[src]

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

This method tests for !=.

impl<'a, 'b> PartialOrd<OsStr> for Cow<'a, Path>
1.8.0
[src]

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

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

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

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

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

impl<'a, 'b> PartialEq<&'b OsStr> for Cow<'a, Path>
1.8.0
[src]

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

This method tests for !=.

impl<'a, 'b> PartialOrd<&'b OsStr> for Cow<'a, Path>
1.8.0
[src]

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

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

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

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

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

impl<'a, 'b> PartialEq<OsString> for Cow<'a, Path>
1.8.0
[src]

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

This method tests for !=.

impl<'a, 'b> PartialOrd<OsString> for Cow<'a, Path>
1.8.0
[src]

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

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

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

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

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