1.0.0[−][src]Enum alloc::borrow::Cow
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);
Another example showing how to keep Cow
in a struct:
use std::borrow::Cow; struct Items<'a, X: 'a> where [X]: ToOwned<Owned = Vec<X>> { values: Cow<'a, [X]>, } impl<'a, X: Clone + 'a> Items<'a, X> where [X]: ToOwned<Owned = Vec<X>> { fn new(v: Cow<'a, [X]>) -> Self { Items { values: v } } } // Creates a container from borrowed values of a slice let readonly = [1, 2]; let borrowed = Items::new((&readonly[..]).into()); match borrowed { Items { values: Cow::Borrowed(b) } => println!("borrowed {:?}", b), _ => panic!("expect borrowed value"), } let mut clone_on_write = borrowed; // Mutates the data from slice into owned vec and pushes a new value on top clone_on_write.values.to_mut().push(3); println!("clone_on_write = {:?}", clone_on_write.values); // The data was mutated. Let check it out. match clone_on_write { Items { values: Cow::Owned(_) } => println!("clone_on_write contains owned data"), _ => panic!("expect owned data"), }
Variants
Borrowed(&'a B)
Borrowed data.
Owned(<B as ToOwned>::Owned)
Owned data.
Methods
impl<'_, B: ?Sized + ToOwned> Cow<'_, B>
[src]
pub fn to_mut(&mut self) -> &mut <B as ToOwned>::Owned
[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::Borrowed("foo"); cow.to_mut().make_ascii_uppercase(); assert_eq!( cow, Cow::Owned(String::from("FOO")) as Cow<str> );
pub fn into_owned(self) -> <B as ToOwned>::Owned
[src]
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(), 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(), String::from(s) );
Trait Implementations
impl<'_> ToString for Cow<'_, str>
1.17.0[src]
impl<'_, B: ?Sized + ToOwned> Deref for Cow<'_, B>
[src]
impl<'a, 'b, B: ?Sized, C: ?Sized> PartialEq<Cow<'b, C>> for Cow<'a, B> where
B: PartialEq<C> + ToOwned,
C: ToOwned,
[src]
B: PartialEq<C> + ToOwned,
C: ToOwned,
fn eq(&self, other: &Cow<'b, C>) -> bool
[src]
#[must_use]
fn ne(&self, other: &Rhs) -> bool
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This method tests for !=
.
impl<'a, 'b> PartialEq<str> for Cow<'a, str>
[src]
impl<'a, 'b> PartialEq<Cow<'a, str>> for str
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impl<'a, 'b> PartialEq<&'b str> for Cow<'a, str>
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impl<'a, 'b> PartialEq<Cow<'a, str>> for &'b str
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impl<'a, 'b> PartialEq<String> for Cow<'a, str>
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impl<'a, 'b> PartialEq<Cow<'a, str>> for String
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impl<'a, 'b, A: Clone, B> PartialEq<&'b [B]> for Cow<'a, [A]> where
A: PartialEq<B>,
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A: PartialEq<B>,
impl<'a, 'b, A: Clone, B> PartialEq<&'b mut [B]> for Cow<'a, [A]> where
A: PartialEq<B>,
[src]
A: PartialEq<B>,
impl<'a, 'b, A: Clone, B> PartialEq<Vec<B>> for Cow<'a, [A]> where
A: PartialEq<B>,
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A: PartialEq<B>,
impl<'_, B: ?Sized> Eq for Cow<'_, B> where
B: Eq + ToOwned,
[src]
B: Eq + ToOwned,
impl<'_, B: ?Sized> Ord for Cow<'_, B> where
B: Ord + ToOwned,
[src]
B: Ord + ToOwned,
fn cmp(&self, other: &Self) -> Ordering
[src]
fn max(self, other: Self) -> Self
1.21.0[src]
Compares and returns the maximum of two values. Read more
fn min(self, other: Self) -> Self
1.21.0[src]
Compares and returns the minimum of two values. Read more
fn clamp(self, min: Self, max: Self) -> Self
[src]
Restrict a value to a certain interval. Read more
impl<'a, B: ?Sized> PartialOrd<Cow<'a, B>> for Cow<'a, B> where
B: PartialOrd + ToOwned,
[src]
B: PartialOrd + ToOwned,
fn partial_cmp(&self, other: &Cow<'a, B>) -> Option<Ordering>
[src]
#[must_use]
fn lt(&self, other: &Rhs) -> bool
[src]
This method tests less than (for self
and other
) and is used by the <
operator. Read more
#[must_use]
fn le(&self, other: &Rhs) -> bool
[src]
This method tests less than or equal to (for self
and other
) and is used by the <=
operator. Read more
#[must_use]
fn gt(&self, other: &Rhs) -> bool
[src]
This method tests greater than (for self
and other
) and is used by the >
operator. Read more
#[must_use]
fn ge(&self, other: &Rhs) -> bool
[src]
This method tests greater than or equal to (for self
and other
) and is used by the >=
operator. Read more
impl<'_, B: ?Sized> Hash for Cow<'_, B> where
B: Hash + ToOwned,
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B: Hash + ToOwned,
fn hash<H: Hasher>(&self, state: &mut H)
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fn hash_slice<H>(data: &[Self], state: &mut H) where
H: Hasher,
1.3.0[src]
H: Hasher,
Feeds a slice of this type into the given [Hasher
]. Read more
impl<'_, B: ?Sized> Display for Cow<'_, B> where
B: Display + ToOwned,
<B as ToOwned>::Owned: Display,
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B: Display + ToOwned,
<B as ToOwned>::Owned: Display,
impl<'_, B: ?Sized> Debug for Cow<'_, B> where
B: Debug + ToOwned,
<B as ToOwned>::Owned: Debug,
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B: Debug + ToOwned,
<B as ToOwned>::Owned: Debug,
impl<'a> Add<&'a str> for Cow<'a, str>
1.14.0[src]
type Output = Cow<'a, str>
The resulting type after applying the +
operator.
fn add(self, rhs: &'a str) -> Self::Output
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impl<'a> Add<Cow<'a, str>> for Cow<'a, str>
1.14.0[src]
type Output = Cow<'a, str>
The resulting type after applying the +
operator.
fn add(self, rhs: Cow<'a, str>) -> Self::Output
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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> Extend<Cow<'a, str>> for String
1.19.0[src]
fn extend<I: IntoIterator<Item = Cow<'a, str>>>(&mut self, iter: I)
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impl<'a> FromIterator<Cow<'a, str>> for String
1.19.0[src]
fn from_iter<I: IntoIterator<Item = Cow<'a, str>>>(iter: I) -> String
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impl<'a> FromIterator<char> for Cow<'a, str>
1.12.0[src]
fn from_iter<I: IntoIterator<Item = char>>(it: I) -> Cow<'a, str>
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impl<'a, 'b> FromIterator<&'b str> for Cow<'a, str>
1.12.0[src]
fn from_iter<I: IntoIterator<Item = &'b str>>(it: I) -> Cow<'a, str>
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impl<'a> FromIterator<String> for Cow<'a, str>
1.12.0[src]
fn from_iter<I: IntoIterator<Item = String>>(it: I) -> Cow<'a, str>
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impl<'a, T> FromIterator<T> for Cow<'a, [T]> where
T: Clone,
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T: Clone,
fn from_iter<I: IntoIterator<Item = T>>(it: I) -> Cow<'a, [T]>
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impl<'_, T: ?Sized + ToOwned> AsRef<T> for Cow<'_, T>
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impl<'a> From<Cow<'a, str>> for String
1.14.0[src]
impl<'a> From<&'a str> for Cow<'a, str>
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impl<'a> From<String> for Cow<'a, str>
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impl<'a> From<&'a String> for Cow<'a, str>
1.28.0[src]
impl<'a, T> From<Cow<'a, [T]>> for Vec<T> where
[T]: ToOwned<Owned = Vec<T>>,
1.14.0[src]
[T]: ToOwned<Owned = Vec<T>>,
impl<'a, T: Clone> From<&'a [T]> for Cow<'a, [T]>
1.8.0[src]
impl<'a, T: Clone> From<Vec<T>> for Cow<'a, [T]>
1.8.0[src]
impl<'a, T: Clone> From<&'a Vec<T>> for Cow<'a, [T]>
1.28.0[src]
impl<'_, B: ?Sized + ToOwned> Clone for Cow<'_, B>
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fn clone(&self) -> Self
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fn clone_from(&mut self, source: &Self)
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impl<'_, B: ?Sized> Default for Cow<'_, B> where
B: ToOwned,
<B as ToOwned>::Owned: Default,
1.11.0[src]
B: ToOwned,
<B as ToOwned>::Owned: Default,
fn default() -> Self
[src]
Creates an owned Cow<'a, B> with the default value for the contained owned value.
impl<'a, B: ?Sized> Borrow<B> for Cow<'a, B> where
B: ToOwned,
<B as ToOwned>::Owned: 'a,
[src]
B: ToOwned,
<B as ToOwned>::Owned: 'a,
Auto Trait Implementations
impl<'a, B: ?Sized> Send for Cow<'a, B> where
B: Sync,
<B as ToOwned>::Owned: Send,
B: Sync,
<B as ToOwned>::Owned: Send,
impl<'a, B: ?Sized> Sync for Cow<'a, B> where
B: Sync,
<B as ToOwned>::Owned: Sync,
B: Sync,
<B as ToOwned>::Owned: Sync,
Blanket Implementations
impl<T> ToOwned for T where
T: Clone,
[src]
T: Clone,
type Owned = T
The resulting type after obtaining ownership.
fn to_owned(&Self) -> T
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fn clone_into(&Self, &mut T)
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impl<T> ToString for T where
T: Display + ?Sized,
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T: Display + ?Sized,
impl<T, U> TryFrom<U> for T where
U: Into<T>,
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U: Into<T>,
type Error = Infallible
The type returned in the event of a conversion error.
fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>
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impl<T, U> Into<U> for T where
U: From<T>,
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U: From<T>,
impl<T> From<T> for T
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impl<T, U> TryInto<U> for T where
U: TryFrom<T>,
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U: TryFrom<T>,
type Error = <U as TryFrom<T>>::Error
The type returned in the event of a conversion error.
fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>
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impl<T> Borrow<T> for T where
T: ?Sized,
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T: ?Sized,
impl<T> BorrowMut<T> for T where
T: ?Sized,
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T: ?Sized,
fn borrow_mut(&mut self) -> &mut T
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impl<T> Any for T where
T: 'static + ?Sized,
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T: 'static + ?Sized,