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.
use std::borrow::Cow;
fn abs_all(input: &mut Cow<[i32]>) {
for i in 0..input.len() {
let v = input[i];
if v < 0 {
input.to_mut()[i] = -v;
}
}
}
let slice = [0, 1, 2];
let mut input = Cow::from(&slice[..]);
abs_all(&mut input);
let slice = [-1, 0, 1];
let mut input = Cow::from(&slice[..]);
abs_all(&mut input);
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, ToOwned};
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 }
}
}
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;
clone_on_write.values.to_mut().push(3);
println!("clone_on_write = {:?}", clone_on_write.values);
match clone_on_write {
Items { values: Cow::Owned(_) } => println!("clone_on_write contains owned data"),
_ => panic!("expect owned data"),
}
Acquires a mutable reference to the owned form of the data.
Clones the data if it is not already owned.
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>
);
Extracts the owned data.
Clones the data if it is not already owned.
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)
);
This method tests for self
and other
values to be equal, and is used by ==
. Read more
This method tests for !=
.
This method tests for self
and other
values to be equal, and is used by ==
. Read more
This method tests for !=
.
This method tests for self
and other
values to be equal, and is used by ==
. Read more
This method tests for !=
.
This method tests for self
and other
values to be equal, and is used by ==
. Read more
This method tests for !=
.
This method tests for self
and other
values to be equal, and is used by ==
. Read more
This method tests for !=
.
This method tests for self
and other
values to be equal, and is used by ==
. Read more
This method tests for !=
.
This method tests for self
and other
values to be equal, and is used by ==
. Read more
This method tests for !=
.
This method tests for self
and other
values to be equal, and is used by ==
. Read more
This method tests for !=
.
This method tests for self
and other
values to be equal, and is used by ==
. Read more
This method tests for !=
.
This method tests for self
and other
values to be equal, and is used by ==
. Read more
This method tests for !=
.
This method tests for self
and other
values to be equal, and is used by ==
. Read more
This method tests for !=
.
This method tests for self
and other
values to be equal, and is used by ==
. Read more
This method tests for !=
.
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
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
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
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
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
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
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
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
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
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
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
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
Formats the value using the given formatter. Read more
The resulting type after applying the +
operator.
Performs the +
operation.
The resulting type after applying the +
operator.
Performs the +
operation.
Performs copy-assignment from source
. Read more
This method tests for self
and other
values to be equal, and is used by ==
. Read more
This method tests for !=
.
This method tests for self
and other
values to be equal, and is used by ==
. Read more
This method tests for !=
.
This method tests for self
and other
values to be equal, and is used by ==
. Read more
This method tests for !=
.
This method tests for self
and other
values to be equal, and is used by ==
. Read more
This method tests for !=
.
This method tests for self
and other
values to be equal, and is used by ==
. Read more
This method tests for !=
.
This method tests for self
and other
values to be equal, and is used by ==
. Read more
This method tests for !=
.
This method tests for self
and other
values to be equal, and is used by ==
. Read more
This method tests for !=
.
Formats the value using the given formatter. Read more
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
The resulting type after dereferencing.
Immutably borrows from an owned value. Read more
This method returns an Ordering
between self
and other
. Read more
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
Creates an owned Cow<'a, B> with the default value for the contained owned value.
Performs the +=
operation.
Performs the +=
operation.
Feeds this value into the given [Hasher
]. Read more
Feeds a slice of this type into the given [Hasher
]. Read more
Converts the given value to a String
. Read more
Creates owned data from borrowed data, usually by cloning. Read more
🔬 This is a nightly-only experimental API. (toowned_clone_into
)
recently added
Uses borrowed data to replace owned data, usually by cloning. Read more
Converts the given value to a String
. Read more
🔬 This is a nightly-only experimental API. (try_from
)
The type returned in the event of a conversion error.
🔬 This is a nightly-only experimental API. (try_from
)
Immutably borrows from an owned value. Read more
Mutably borrows from an owned value. Read more
🔬 This is a nightly-only experimental API. (try_from
)
The type returned in the event of a conversion error.
🔬 This is a nightly-only experimental API. (try_from
)
🔬 This is a nightly-only experimental API. (get_type_id
)
this method will likely be replaced by an associated static
Convert Box<Trait>
(where Trait: Downcast
) to Box<Any>
. Box<Any>
can then be further downcast
into Box<ConcreteType>
where ConcreteType
implements Trait
. Read more
Convert &Trait
(where Trait: Downcast
) to &Any
. This is needed since Rust cannot generate &Any
's vtable from &Trait
's. Read more
Convert &mut Trait
(where Trait: Downcast
) to &Any
. This is needed since Rust cannot generate &mut Any
's vtable from &mut Trait
's. Read more