Enum collections::borrow::Cow 1.0.0
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pub enum Cow<'a, B> where
B: 'a + ToOwned + ?Sized, {
Borrowed(&'a B),
Owned(<B as ToOwned>::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);
Variants
Borrowed(&'a B)
Borrowed data.
Owned(<B as ToOwned>::Owned)
Owned data.
Methods
impl<'a, B> Cow<'a, B> where
B: ToOwned + ?Sized,
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B: ToOwned + ?Sized,
fn to_mut(&mut self) -> &mut <B as ToOwned>::Owned
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Acquires a mutable reference to the owned form of the data.
Clones the data if it is not already owned.
Examples
use std::ascii::AsciiExt; use std::borrow::Cow; let mut cow = Cow::Borrowed("foo"); cow.to_mut().make_ascii_uppercase(); assert_eq!( cow, Cow::Owned(String::from("FOO")) as Cow<str> );
fn into_owned(self) -> <B as ToOwned>::Owned
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Extracts the owned data.
Clones the data if it is not already owned.
Examples
Calling into_owned
on a Cow::Borrowed
clones the underlying data
and becomes a Cow::Owned
:
use std::borrow::Cow; let s = "Hello world!"; let cow = Cow::Borrowed(s); assert_eq!( cow.into_owned(), Cow::Owned(String::from(s)) );
Calling into_owned
on a Cow::Owned
is a no-op:
use std::borrow::Cow; let s = "Hello world!"; let cow: Cow<str> = Cow::Owned(String::from(s)); assert_eq!( cow.into_owned(), Cow::Owned(String::from(s)) );
Trait Implementations
impl<'a, B> Debug for Cow<'a, B> where
B: Debug + ToOwned + ?Sized,
<B as ToOwned>::Owned: Debug,
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B: Debug + ToOwned + ?Sized,
<B as ToOwned>::Owned: Debug,
fn fmt(&self, f: &mut Formatter) -> Result<(), Error>
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Formats the value using the given formatter.
impl<'a, T> AsRef<T> for Cow<'a, T> where
T: ToOwned + ?Sized,
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T: ToOwned + ?Sized,
impl<'a, B> Borrow<B> for Cow<'a, B> where
B: ToOwned + ?Sized,
<B as ToOwned>::Owned: 'a,
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B: ToOwned + ?Sized,
<B as ToOwned>::Owned: 'a,
impl<'a, B> Eq for Cow<'a, B> where
B: Eq + ToOwned + ?Sized,
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B: Eq + ToOwned + ?Sized,
impl<'a, T> From<Vec<T>> for Cow<'a, [T]> where
T: Clone,
1.8.0[src]
T: Clone,
impl<'a> From<String> for Cow<'a, str>
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impl<'a, T> From<&'a [T]> for Cow<'a, [T]> where
T: Clone,
1.8.0[src]
T: Clone,
impl<'a> From<&'a str> for Cow<'a, str>
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impl<'a, B> Display for Cow<'a, B> where
B: Display + ToOwned + ?Sized,
<B as ToOwned>::Owned: Display,
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B: Display + ToOwned + ?Sized,
<B as ToOwned>::Owned: Display,
fn fmt(&self, f: &mut Formatter) -> Result<(), Error>
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Formats the value using the given formatter. Read more
impl<'a> Add<&'a str> for Cow<'a, str>
1.14.0[src]
type Output = Cow<'a, str>
fn add(self, rhs: &'a str) -> <Cow<'a, str> as Add<&'a str>>::Output
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impl<'a> Add<Cow<'a, str>> for Cow<'a, str>
1.14.0[src]
type Output = Cow<'a, str>
fn add(self, rhs: Cow<'a, str>) -> <Cow<'a, str> as Add<Cow<'a, str>>>::Output
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impl<'a, 'b, A, B> PartialEq<&'b [B]> for Cow<'a, [A]> where
A: Clone + PartialEq<B>,
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A: Clone + PartialEq<B>,
impl<'a, 'b, A, B> PartialEq<Vec<B>> for Cow<'a, [A]> where
A: Clone + PartialEq<B>,
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A: Clone + PartialEq<B>,
impl<'a, 'b, B, C> PartialEq<Cow<'b, C>> for Cow<'a, B> where
B: PartialEq<C> + ToOwned + ?Sized,
C: ToOwned + ?Sized,
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B: PartialEq<C> + ToOwned + ?Sized,
C: ToOwned + ?Sized,
impl<'a, 'b, A, B> PartialEq<&'b mut [B]> for Cow<'a, [A]> where
A: Clone + PartialEq<B>,
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A: Clone + PartialEq<B>,
impl<'a, 'b> PartialEq<&'b str> for Cow<'a, str>
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impl<'a, 'b> PartialEq<String> for Cow<'a, str>
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impl<'a, 'b> PartialEq<str> for Cow<'a, str>
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impl<'a> FromIterator<char> for Cow<'a, str>
1.12.0[src]
fn from_iter<I>(it: I) -> Cow<'a, str> where
I: IntoIterator<Item = char>,
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I: IntoIterator<Item = char>,
impl<'a> FromIterator<String> for Cow<'a, str>
1.12.0[src]
fn from_iter<I>(it: I) -> Cow<'a, str> where
I: IntoIterator<Item = String>,
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I: IntoIterator<Item = String>,
impl<'a, 'b> FromIterator<&'b str> for Cow<'a, str>
1.12.0[src]
fn from_iter<I>(it: I) -> Cow<'a, str> where
I: IntoIterator<Item = &'b str>,
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I: IntoIterator<Item = &'b str>,
impl<'a, T> FromIterator<T> for Cow<'a, [T]> where
T: Clone,
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T: Clone,
fn from_iter<I>(it: I) -> Cow<'a, [T]> where
I: IntoIterator<Item = T>,
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I: IntoIterator<Item = T>,
impl<'a, B> PartialOrd<Cow<'a, B>> for Cow<'a, B> where
B: PartialOrd<B> + ToOwned + ?Sized,
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B: PartialOrd<B> + ToOwned + ?Sized,
fn partial_cmp(&self, other: &Cow<'a, B>) -> Option<Ordering>
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impl<'a, B> Clone for Cow<'a, B> where
B: ToOwned + ?Sized,
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B: ToOwned + ?Sized,
impl<'a, B> Hash for Cow<'a, B> where
B: Hash + ToOwned + ?Sized,
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B: Hash + ToOwned + ?Sized,
impl<'a, B> Deref for Cow<'a, B> where
B: ToOwned + ?Sized,
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B: ToOwned + ?Sized,
impl<'a, B> Ord for Cow<'a, B> where
B: Ord + ToOwned + ?Sized,
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B: Ord + ToOwned + ?Sized,
impl<'a> ToString for Cow<'a, str>
1.17.0[src]
impl<'a> AddAssign<&'a str> for Cow<'a, str>
1.14.0[src]
fn add_assign(&mut self, rhs: &'a str)
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impl<'a> AddAssign<Cow<'a, str>> for Cow<'a, str>
1.14.0[src]
fn add_assign(&mut self, rhs: Cow<'a, str>)
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impl<'a, B> Default for Cow<'a, B> where
B: ToOwned + ?Sized,
<B as ToOwned>::Owned: Default,
1.11.0[src]
B: ToOwned + ?Sized,
<B as ToOwned>::Owned: Default,