Enum std::borrow::Cow

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

[−] Expand description

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);

Variants

Borrowed(&'a B)

[−] Expand description

Borrowed data.

Owned(B::Owned)

[−] Expand description

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

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

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> AddAssign<&'a str> for Cow<'a, str>

fn add_assign(&mut self, rhs: &'a str)[−]

The method for the += operator

impl<'a> AddAssign<Cow<'a, str>> for Cow<'a, str>

fn add_assign(&mut self, rhs: Cow<'a, str>)[−]

The method for the += operator

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

fn default() -> Cow<'a, B>[−]

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

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

fn hash<H>(&self, state: &mut H) where H: Hasher[−]

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

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

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

fn from(s: &'a [T]) -> Cow<'a, [T]>[−]

Performs the conversion.

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

fn from(v: Vec<T>) -> Cow<'a, [T]>[−]

Performs the conversion.

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

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> Add<&'a str> for Cow<'a, str>

type Output = Cow<'a, str>

The resulting type after applying the + operator

fn add(self, rhs: &'a str) -> Cow<'a, str>::Output[−]

The method for the + operator

impl<'a> Add<Cow<'a, str>> for Cow<'a, str>

type Output = Cow<'a, str>

The resulting type after applying the + operator

fn add(self, rhs: Cow<'a, str>) -> Cow<'a, str>::Output[−]

The method for the + operator

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

type Target = B

The resulting type after dereferencing

fn deref(&self) -> &B[−]

The method called to dereference a value

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

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

fn as_ref(&self) -> &T[−]

Performs the conversion.

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

fn borrow(&self) -> &B[−]

Immutably borrows from an owned value.

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

fn fmt(&self, f: &mut Formatter) -> Result<(), Error>[−]

Formats the value using the given formatter.

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

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

This method returns an Ordering between self and other.

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

fn from_iter<I>(it: I) -> Cow<'a, str> where I: IntoIterator<Item=char>[−]

Creates a value from an iterator.

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

fn from_iter<I>(it: I) -> Cow<'a, str> where I: IntoIterator<Item=&'b str>[−]

Creates a value from an iterator.

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

fn from_iter<I>(it: I) -> Cow<'a, str> where I: IntoIterator<Item=String>[−]

Creates a value from an iterator.

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>[−]

Creates a value from an iterator.

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

fn fmt(&self, f: &mut Formatter) -> Result<(), Error>[−]

Formats the value using the given formatter.

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

fn eq(&self, other: &OsStr) -> 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> PartialOrd<OsStr> for Cow<'a, OsStr>

fn partial_cmp(&self, other: &OsStr) -> 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> PartialEq<&'b OsStr> for Cow<'a, OsStr>

fn eq(&self, other: &&'b OsStr) -> 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> PartialOrd<&'b OsStr> for Cow<'a, OsStr>

fn partial_cmp(&self, other: &&'b OsStr) -> 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> PartialEq<OsString> for Cow<'a, OsStr>

fn eq(&self, other: &OsString) -> 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> PartialOrd<OsString> for Cow<'a, OsStr>

fn partial_cmp(&self, other: &OsString) -> 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> From<&'a Path> for Cow<'a, Path>

fn from(s: &'a Path) -> Cow<'a, Path>[−]

Performs the conversion.

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

fn from(s: PathBuf) -> Cow<'a, Path>[−]

Performs the conversion.

impl<'a> AsRef<Path> for Cow<'a, OsStr>

fn as_ref(&self) -> &Path[−]

Performs the conversion.

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

fn eq(&self, other: &Path) -> 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> PartialOrd<Path> for Cow<'a, Path>

fn partial_cmp(&self, other: &Path) -> 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> PartialEq<&'b Path> for Cow<'a, Path>

fn eq(&self, other: &&'b Path) -> 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> PartialOrd<&'b Path> for Cow<'a, Path>

fn partial_cmp(&self, other: &&'b Path) -> 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> PartialEq<PathBuf> for Cow<'a, Path>

fn eq(&self, other: &PathBuf) -> 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> PartialOrd<PathBuf> for Cow<'a, Path>

fn partial_cmp(&self, other: &PathBuf) -> 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> PartialEq<PathBuf> for Cow<'a, OsStr>

fn eq(&self, other: &PathBuf) -> 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> PartialOrd<PathBuf> for Cow<'a, OsStr>

fn partial_cmp(&self, other: &PathBuf) -> 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> PartialEq<Path> for Cow<'a, OsStr>

fn eq(&self, other: &Path) -> 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> PartialOrd<Path> for Cow<'a, OsStr>

fn partial_cmp(&self, other: &Path) -> 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> PartialEq<&'a Path> for Cow<'b, OsStr>

fn eq(&self, other: &&'a Path) -> 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> PartialOrd<&'a Path> for Cow<'b, OsStr>

fn partial_cmp(&self, other: &&'a Path) -> 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> PartialEq<OsStr> for Cow<'a, Path>

fn eq(&self, other: &OsStr) -> 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> PartialOrd<OsStr> for Cow<'a, Path>

fn partial_cmp(&self, other: &OsStr) -> 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> PartialEq<&'b OsStr> for Cow<'a, Path>

fn eq(&self, other: &&'b OsStr) -> 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> PartialOrd<&'b OsStr> for Cow<'a, Path>

fn partial_cmp(&self, other: &&'b OsStr) -> 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> PartialEq<OsString> for Cow<'a, Path>

fn eq(&self, other: &OsString) -> 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> PartialOrd<OsString> for Cow<'a, Path>

fn partial_cmp(&self, other: &OsString) -> 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.