Enum otter::prelude::Cow 1.0.0[−][src]
pub enum Cow<'a, B> where
B: 'a + ToOwned + ?Sized, { Borrowed(&'a B), Owned(<B as ToOwned>::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.
If you need reference-counting pointers, note that
Rc::make_mut
and
Arc::make_mut
can provide clone-on-write
functionality as well.
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 data.
Implementations
🔬 This is a nightly-only experimental API. (cow_is_borrowed
)
cow_is_borrowed
)Returns true if the data is borrowed, i.e. if to_mut
would require additional work.
Examples
#![feature(cow_is_borrowed)] use std::borrow::Cow; let cow = Cow::Borrowed("moo"); assert!(cow.is_borrowed()); let bull: Cow<'_, str> = Cow::Owned("...moo?".to_string()); assert!(!bull.is_borrowed());
🔬 This is a nightly-only experimental API. (cow_is_borrowed
)
cow_is_borrowed
)Returns true if the data is owned, i.e. if to_mut
would be a no-op.
Examples
#![feature(cow_is_borrowed)] use std::borrow::Cow; let cow: Cow<'_, str> = Cow::Owned("moo".to_string()); assert!(cow.is_owned()); let bull = Cow::Borrowed("...moo?"); assert!(!bull.is_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::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.
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
Performs the +=
operation. Read more
Performs the +=
operation. Read more
impl<'de, 'a, T> Deserialize<'de> for Cow<'a, T> where
T: ToOwned + ?Sized,
<T as ToOwned>::Owned: Deserialize<'de>,
[src]
impl<'de, 'a, T> Deserialize<'de> for Cow<'a, T> where
T: ToOwned + ?Sized,
<T as ToOwned>::Owned: Deserialize<'de>,
[src]pub fn deserialize<D>(
deserializer: D
) -> Result<Cow<'a, T>, <D as Deserializer<'de>>::Error> where
D: Deserializer<'de>,
[src]
pub fn deserialize<D>(
deserializer: D
) -> Result<Cow<'a, T>, <D as Deserializer<'de>>::Error> where
D: Deserializer<'de>,
[src]Deserialize this value from the given Serde deserializer. Read more
Extends a collection with the contents of an iterator. Read more
extend_one
)Extends a collection with exactly one element.
extend_one
)Reserves capacity in a collection for the given number of additional elements. Read more
Extends a collection with the contents of an iterator. Read more
extend_one
)Extends a collection with exactly one element.
extend_one
)Reserves capacity in a collection for the given number of additional elements. Read more
Convert a clone-on-write slice into a vector.
If s
already owns a Vec<T>
, it will be returned directly.
If s
is borrowing a slice, a new Vec<T>
will be allocated and
filled by cloning s
’s items into it.
Examples
let o: Cow<[i32]> = Cow::Owned(vec![1, 2, 3]); let b: Cow<[i32]> = Cow::Borrowed(&[1, 2, 3]); assert_eq!(Vec::from(o), Vec::from(b));
Convert copy-on-write string to Value
Examples
use serde_json::Value; use std::borrow::Cow; let s: Cow<str> = Cow::Borrowed("lorem"); let x: Value = s.into();
use serde_json::Value; use std::borrow::Cow; let s: Cow<str> = Cow::Owned("lorem".to_string()); let x: Value = s.into();
Converts a Cow
into a box of dyn Error
+ Send
+ Sync
.
Examples
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::<dyn Error + Send + Sync>::from(a_cow_str_error); assert!( mem::size_of::<Box<dyn Error + Send + Sync>>() == mem::size_of_val(&a_boxed_error))
Performs the conversion.
Performs the conversion.
type Deserializer = CowStrDeserializer<'a, E>
type Deserializer = CowStrDeserializer<'a, E>
The type of the deserializer being converted into.
Convert this value into a deserializer.
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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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
pub fn serialize<S>(
&self,
serializer: S
) -> Result<<S as Serializer>::Ok, <S as Serializer>::Error> where
S: Serializer,
[src]
pub fn serialize<S>(
&self,
serializer: S
) -> Result<<S as Serializer>::Ok, <S as Serializer>::Error> where
S: Serializer,
[src]Serialize this value into the given Serde serializer. Read more
Auto Trait Implementations
impl<'a, B: ?Sized> RefUnwindSafe for Cow<'a, B> where
B: RefUnwindSafe,
<B as ToOwned>::Owned: RefUnwindSafe,
impl<'a, B: ?Sized> UnwindSafe for Cow<'a, B> where
B: RefUnwindSafe,
<B as ToOwned>::Owned: UnwindSafe,
Blanket Implementations
Mutably borrows from an owned value. Read more
Convert Box<dyn Trait>
(where Trait: Downcast
) to Box<dyn Any>
. Box<dyn Any>
can
then be further downcast
into Box<ConcreteType>
where ConcreteType
implements Trait
. Read more
Convert Rc<Trait>
(where Trait: Downcast
) to Rc<Any>
. Rc<Any>
can then be
further downcast
into Rc<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
pub fn dyn_cast<T>(
self
) -> Result<<A as DynCastExtHelper<T>>::Target, <A as DynCastExtHelper<T>>::Source> where
T: ?Sized,
A: DynCastExtHelper<T>,
[src]
pub fn dyn_cast<T>(
self
) -> Result<<A as DynCastExtHelper<T>>::Target, <A as DynCastExtHelper<T>>::Source> where
T: ?Sized,
A: DynCastExtHelper<T>,
[src]Use this to cast from one trait object type to another. Read more
pub fn dyn_upcast<T>(self) -> <A as DynCastExtAdvHelper<T, T>>::Target where
T: ?Sized,
A: DynCastExtAdvHelper<T, T, Source = <A as DynCastExtAdvHelper<T, T>>::Target>,
[src]
pub fn dyn_upcast<T>(self) -> <A as DynCastExtAdvHelper<T, T>>::Target where
T: ?Sized,
A: DynCastExtAdvHelper<T, T, Source = <A as DynCastExtAdvHelper<T, T>>::Target>,
[src]Use this to upcast a trait to one of its supertraits. Read more
pub fn dyn_cast_adv<F, T>(
self
) -> Result<<A as DynCastExtAdvHelper<F, T>>::Target, <A as DynCastExtAdvHelper<F, T>>::Source> where
F: ?Sized,
T: ?Sized,
A: DynCastExtAdvHelper<F, T>,
[src]
pub fn dyn_cast_adv<F, T>(
self
) -> Result<<A as DynCastExtAdvHelper<F, T>>::Target, <A as DynCastExtAdvHelper<F, T>>::Source> where
F: ?Sized,
T: ?Sized,
A: DynCastExtAdvHelper<F, T>,
[src]pub fn dyn_cast_with_config<C>(
self
) -> Result<<A as DynCastExtAdvHelper<<C as DynCastConfig>::Source, <C as DynCastConfig>::Target>>::Target, <A as DynCastExtAdvHelper<<C as DynCastConfig>::Source, <C as DynCastConfig>::Target>>::Source> where
C: DynCastConfig,
A: DynCastExtAdvHelper<<C as DynCastConfig>::Source, <C as DynCastConfig>::Target>,
[src]
pub fn dyn_cast_with_config<C>(
self
) -> Result<<A as DynCastExtAdvHelper<<C as DynCastConfig>::Source, <C as DynCastConfig>::Target>>::Target, <A as DynCastExtAdvHelper<<C as DynCastConfig>::Source, <C as DynCastConfig>::Target>>::Source> where
C: DynCastConfig,
A: DynCastExtAdvHelper<<C as DynCastConfig>::Source, <C as DynCastConfig>::Target>,
[src]Use this to cast from one trait object type to another. With this method the type parameter is a config type that uniquely specifies which cast should be preformed. Read more
type Output = T
type Output = T
Should always be Self
pub fn vzip(self) -> V