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);Run
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"),
}Run
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>
);Run
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)
);Run
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)
);Run
The resulting type after applying the + operator.
Performs the + operation.
The resulting type after applying the + operator.
Performs the + operation.
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
Creates an owned Cow<'a, B> with the default value for the contained owned value.
Immutably borrows from an owned value. Read more
Feeds this value into the given [Hasher]. Read more
Feeds a slice of this type into the given [Hasher]. 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
Performs copy-assignment from source. Read more
Performs the += operation.
Performs the += operation.
Converts the given value to a String. Read more
Extends a collection with the contents of an iterator. 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 !=.
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
type Target = B
The resulting type after dereferencing.
Converts a Cow into a box of dyn Error + Send + Sync.
use std::error::Error;
use std::mem;
use std::borrow::Cow;
let a_cow_str_error = Cow::from("a str error");
let a_boxed_error = Box::<Error + Send + Sync>::from(a_cow_str_error);
assert!(
mem::size_of::<Box<dyn Error + Send + Sync>>() == mem::size_of_val(&a_boxed_error))Run
Converts a Cow into a box of dyn Error.
use std::error::Error;
use std::mem;
use std::borrow::Cow;
let a_cow_str_error = Cow::from("a str error");
let a_boxed_error = Box::<Error>::from(a_cow_str_error);
assert!(mem::size_of::<Box<dyn Error>>() == mem::size_of_val(&a_boxed_error))Run
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 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
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
type Error = !
🔬 This is a nightly-only experimental API. (
try_from #33417)
The type returned in the event of a conversion error.
🔬 This is a nightly-only experimental API. (
try_from #33417)
type Error = <U as TryFrom<T>>::Error
🔬 This is a nightly-only experimental API. (
try_from #33417)
The type returned in the event of a conversion error.
🔬 This is a nightly-only experimental API. (
try_from #33417)
Immutably borrows from an owned value. Read more
Mutably borrows from an owned value. Read more
🔬 This is a nightly-only experimental API. (get_type_id #27745)
this method will likely be replaced by an associated static
type Owned = T
Creates owned data from borrowed data, usually by cloning. Read more
🔬 This is a nightly-only experimental API. (toowned_clone_into #41263)
recently added
Uses borrowed data to replace owned data, usually by cloning. Read more
Converts the given value to a String. Read more