# Enum std::borrow::Cow [−] [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

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` | Borrowed data.
`Owned` | Owned data.

## Methods

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

#### `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> Borrow<B> for Cow<'a, B> where B: ToOwned + ?Sized, B::Owned: 'a`

#### `fn borrow(&self) -> &B`

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

#### `fn clone(&self) -> Cow<'a, B>`

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

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

#### `type Target = B`

#### `fn deref(&self) -> &B`

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

### `impl<'a, B> IntoCow<'a, B> for Cow<'a, B> where B: ToOwned + ?Sized`

#### `fn into_cow(self) -> Cow<'a, B>`

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

#### `fn as_ref(&self) -> &T`

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

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

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

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

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

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

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

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

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

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

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

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

#### `fn from(s: String) -> Cow<'a, str>`

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

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

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

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

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

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

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

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

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

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

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

### `impl<'a> From<&'a Path> for Cow<'a, Path>`

#### `fn from(s: &'a Path) -> Cow<'a, Path>`

### `impl<'a> From<PathBuf> for Cow<'a, Path>`

#### `fn from(s: PathBuf) -> Cow<'a, Path>`

### `impl<'a, 'b> PartialEq<Path> for Cow<'a, Path>`

#### `fn eq(&self, other: &Path) -> bool`

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

### `impl<'a, 'b> PartialEq<&'b Path> for Cow<'a, Path>`

#### `fn eq(&self, other: &&'b Path) -> bool`

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

### `impl<'a, 'b> PartialEq<PathBuf> for Cow<'a, Path>`

#### `fn eq(&self, other: &PathBuf) -> bool`

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

# Help

## Keyboard Shortcuts

?
  Show this help dialog
S
  Focus the search field
⇤
  Move up in search results
⇥
  Move down in search results
⏎
  Go to active search result

## Search Tricks

Prefix searches with a type followed by a colon (e.g. `fn:`) to restrict the search to a given type.

Accepted types are: `fn`, `mod`, `struct`, `enum`, `trait`, `type`, `macro`, and `const`.

Search functions by type signature (e.g. `vec -> usize`)