simd_json ::cow Enum Cow Copy item path 1.0.0 · source pub enum Cow<'a, B>{
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 {
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;
struct Items<'a , X> 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" ),
}
🔬 This is a nightly-only experimental API. (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
)
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
returns a clone of the borrowed data:
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
returns the owned data. The data is moved out of the
Cow
without being cloned.
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)
);
The resulting type after applying the +
operator.
The resulting type after applying the +
operator.
Converts this type into a shared reference of the (usually inferred) input type.
Converts this type into a shared reference of the (usually inferred) input type.
Immutably borrows from an owned value.
Read more Performs copy-assignment from
source
.
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.
The resulting type after dereferencing.
Dereferences the value.
Deserialize this value from the given Serde deserializer.
Read more Formats the value using the given formatter.
Read more Creates a Borrowed
variant of Cow
from a slice.
This conversion does not allocate or clone the data.
Creates a Borrowed
variant of Cow
from a reference to an array.
This conversion does not allocate or clone the data.
Converts a CStr
into a borrowed Cow
without copying or allocating.
Converts a &
CString
into a borrowed Cow
without copying or allocating.
Creates a clone-on-write pointer from a reference to
Path
.
This conversion does not clone or allocate.
Creates a clone-on-write pointer from a reference to
PathBuf
.
This conversion does not clone or allocate.
Converts a String
reference into a Borrowed
variant.
No heap allocation is performed, and the string
is not copied.
§ Example
let s = "eggplant" .to_string();
assert_eq! (Cow::from(& s), Cow::Borrowed("eggplant" ));
Creates a Borrowed
variant of Cow
from a reference to Vec
.
This conversion does not allocate or clone the data.
Converts a string slice into a Borrowed
variant.
No heap allocation is performed, and the string
is not copied.
§ Example
assert_eq! (Cow::from("eggplant" ), Cow::Borrowed("eggplant" ));
Converts a CString
into an owned Cow
without copying or allocating.
Converts 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));
Converts to this type from the input type.
Converts to this type from the input type.
Converts to this type from the input type.
Creates a clone-on-write pointer from an owned
instance of PathBuf
.
This conversion does not clone or allocate.
Converts a String
into an Owned
variant.
No heap allocation is performed, and the string
is not copied.
§ Example
let s = "eggplant" .to_string();
let s2 = "eggplant" .to_string();
assert_eq! (Cow::from(s), Cow::<'static , str>::Owned(s2));
Creates an Owned
variant of Cow
from an owned instance of Vec
.
This conversion does not allocate or clone the data.
The type of the deserializer being converted into.
Convert this value into a deserializer.
Compares and returns the maximum of two values.
Read more Compares and returns the minimum of two values.
Read more Restrict a value to a certain interval.
Read more Tests for self
and other
values to be equal, and is used by ==
.
Tests for !=
. The default implementation is almost always sufficient,
and should not be overridden without very good reason.
Tests for self
and other
values to be equal, and is used by ==
.
Tests for !=
. The default implementation is almost always sufficient,
and should not be overridden without very good reason.
Tests for self
and other
values to be equal, and is used by ==
.
Tests for !=
. The default implementation is almost always sufficient,
and should not be overridden without very good reason.
Tests for self
and other
values to be equal, and is used by ==
.
Tests for !=
. The default implementation is almost always sufficient,
and should not be overridden without very good reason.
Tests for self
and other
values to be equal, and is used by ==
.
Tests for !=
. The default implementation is almost always sufficient,
and should not be overridden without very good reason.
Tests for self
and other
values to be equal, and is used by ==
.
Tests for !=
. The default implementation is almost always sufficient,
and should not be overridden without very good reason.
Tests for self
and other
values to be equal, and is used by ==
.
Tests for !=
. The default implementation is almost always sufficient,
and should not be overridden without very good reason.
Tests for self
and other
values to be equal, and is used by ==
.
Tests for !=
. The default implementation is almost always sufficient,
and should not be overridden without very good reason.
Tests for self
and other
values to be equal, and is used by ==
.
Tests for !=
. The default implementation is almost always sufficient,
and should not be overridden without very good reason.
Tests for self
and other
values to be equal, and is used by ==
.
Tests for !=
. The default implementation is almost always sufficient,
and should not be overridden without very good reason.
Tests for self
and other
values to be equal, and is used by ==
.
Tests for !=
. The default implementation is almost always sufficient,
and should not be overridden without very good reason.
Tests for self
and other
values to be equal, and is used by ==
.
Tests for !=
. The default implementation is almost always sufficient,
and should not be overridden without very good reason.
Tests for self
and other
values to be equal, and is used by ==
.
Tests for !=
. The default implementation is almost always sufficient,
and should not be overridden without very good reason.
Tests for self
and other
values to be equal, and is used by ==
.
Tests for !=
. The default implementation is almost always sufficient,
and should not be overridden without very good reason.
Tests for self
and other
values to be equal, and is used by ==
.
Tests for !=
. The default implementation is almost always sufficient,
and should not be overridden without very good reason.
Tests for self
and other
values to be equal, and is used by ==
.
Tests for !=
. The default implementation is almost always sufficient,
and should not be overridden without very good reason.
Tests for self
and other
values to be equal, and is used by ==
.
Tests for !=
. The default implementation is almost always sufficient,
and should not be overridden without very good reason.
Tests for self
and other
values to be equal, and is used by ==
.
Tests for !=
. The default implementation is almost always sufficient,
and should not be overridden without very good reason.
Tests for self
and other
values to be equal, and is used by ==
.
Tests for !=
. The default implementation is almost always sufficient,
and should not be overridden without very good reason.
Tests for self
and other
values to be equal, and is used by ==
.
Tests for !=
. The default implementation is almost always sufficient,
and should not be overridden without very good reason.
Tests for self
and other
values to be equal, and is used by ==
.
Tests for !=
. The default implementation is almost always sufficient,
and should not be overridden without very good reason.
Tests for self
and other
values to be equal, and is used by ==
.
Tests for !=
. The default implementation is almost always sufficient,
and should not be overridden without very good reason.
Tests for self
and other
values to be equal, and is used by ==
.
Tests for !=
. The default implementation is almost always sufficient,
and should not be overridden without very good reason.
Tests for self
and other
values to be equal, and is used by ==
.
Tests for !=
. The default implementation is almost always sufficient,
and should not be overridden without very good reason.
Tests for self
and other
values to be equal, and is used by ==
.
Tests for !=
. The default implementation is almost always sufficient,
and should not be overridden without very good reason.
Tests for self
and other
values to be equal, and is used by ==
.
Tests for !=
. The default implementation is almost always sufficient,
and should not be overridden without very good reason.
Tests for self
and other
values to be equal, and is used by ==
.
Tests for !=
. The default implementation is almost always sufficient,
and should not be overridden without very good reason.
Tests for self
and other
values to be equal, and is used by ==
.
Tests for !=
. The default implementation is almost always sufficient,
and should not be overridden without very good reason.
Tests for self
and other
values to be equal, and is used by ==
.
Tests for !=
. The default implementation is almost always sufficient,
and should not be overridden without very good reason.
Tests for self
and other
values to be equal, and is used by ==
.
Tests for !=
. The default implementation is almost always sufficient,
and should not be overridden without very good reason.
This method returns an ordering between
self
and
other
values if one exists.
Read more Tests less than (for
self
and
other
) and is used by the
<
operator.
Read more Tests less than or equal to (for
self
and
other
) and is used by the
<=
operator.
Read more Tests greater than (for
self
and
other
) and is used by the
>
operator.
Read more 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 Tests less than (for
self
and
other
) and is used by the
<
operator.
Read more Tests less than or equal to (for
self
and
other
) and is used by the
<=
operator.
Read more Tests greater than (for
self
and
other
) and is used by the
>
operator.
Read more 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 Tests less than (for
self
and
other
) and is used by the
<
operator.
Read more Tests less than or equal to (for
self
and
other
) and is used by the
<=
operator.
Read more Tests greater than (for
self
and
other
) and is used by the
>
operator.
Read more 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 Tests less than (for
self
and
other
) and is used by the
<
operator.
Read more Tests less than or equal to (for
self
and
other
) and is used by the
<=
operator.
Read more Tests greater than (for
self
and
other
) and is used by the
>
operator.
Read more 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 Tests less than (for
self
and
other
) and is used by the
<
operator.
Read more Tests less than or equal to (for
self
and
other
) and is used by the
<=
operator.
Read more Tests greater than (for
self
and
other
) and is used by the
>
operator.
Read more 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 Tests less than (for
self
and
other
) and is used by the
<
operator.
Read more Tests less than or equal to (for
self
and
other
) and is used by the
<=
operator.
Read more Tests greater than (for
self
and
other
) and is used by the
>
operator.
Read more 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 Tests less than (for
self
and
other
) and is used by the
<
operator.
Read more Tests less than or equal to (for
self
and
other
) and is used by the
<=
operator.
Read more Tests greater than (for
self
and
other
) and is used by the
>
operator.
Read more 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 Tests less than (for
self
and
other
) and is used by the
<
operator.
Read more Tests less than or equal to (for
self
and
other
) and is used by the
<=
operator.
Read more Tests greater than (for
self
and
other
) and is used by the
>
operator.
Read more 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 Tests less than (for
self
and
other
) and is used by the
<
operator.
Read more Tests less than or equal to (for
self
and
other
) and is used by the
<=
operator.
Read more Tests greater than (for
self
and
other
) and is used by the
>
operator.
Read more 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 Tests less than (for
self
and
other
) and is used by the
<
operator.
Read more Tests less than or equal to (for
self
and
other
) and is used by the
<=
operator.
Read more Tests greater than (for
self
and
other
) and is used by the
>
operator.
Read more 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 Tests less than (for
self
and
other
) and is used by the
<
operator.
Read more Tests less than or equal to (for
self
and
other
) and is used by the
<=
operator.
Read more Tests greater than (for
self
and
other
) and is used by the
>
operator.
Read more 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 Tests less than (for
self
and
other
) and is used by the
<
operator.
Read more Tests less than or equal to (for
self
and
other
) and is used by the
<=
operator.
Read more Tests greater than (for
self
and
other
) and is used by the
>
operator.
Read more 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 Tests less than (for
self
and
other
) and is used by the
<
operator.
Read more Tests less than or equal to (for
self
and
other
) and is used by the
<=
operator.
Read more Tests greater than (for
self
and
other
) and is used by the
>
operator.
Read more 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 Tests less than (for
self
and
other
) and is used by the
<
operator.
Read more Tests less than or equal to (for
self
and
other
) and is used by the
<=
operator.
Read more Tests greater than (for
self
and
other
) and is used by the
>
operator.
Read more 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 Tests less than (for
self
and
other
) and is used by the
<
operator.
Read more Tests less than or equal to (for
self
and
other
) and is used by the
<=
operator.
Read more Tests greater than (for
self
and
other
) and is used by the
>
operator.
Read more 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 Tests less than (for
self
and
other
) and is used by the
<
operator.
Read more Tests less than or equal to (for
self
and
other
) and is used by the
<=
operator.
Read more Tests greater than (for
self
and
other
) and is used by the
>
operator.
Read more 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 Tests less than (for
self
and
other
) and is used by the
<
operator.
Read more Tests less than or equal to (for
self
and
other
) and is used by the
<=
operator.
Read more Tests greater than (for
self
and
other
) and is used by the
>
operator.
Read more 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 Tests less than (for
self
and
other
) and is used by the
<
operator.
Read more Tests less than or equal to (for
self
and
other
) and is used by the
<=
operator.
Read more Tests greater than (for
self
and
other
) and is used by the
>
operator.
Read more 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 Tests less than (for
self
and
other
) and is used by the
<
operator.
Read more Tests less than or equal to (for
self
and
other
) and is used by the
<=
operator.
Read more Tests greater than (for
self
and
other
) and is used by the
>
operator.
Read more 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 Tests less than (for
self
and
other
) and is used by the
<
operator.
Read more Tests less than or equal to (for
self
and
other
) and is used by the
<=
operator.
Read more Tests greater than (for
self
and
other
) and is used by the
>
operator.
Read more 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 Tests less than (for
self
and
other
) and is used by the
<
operator.
Read more Tests less than or equal to (for
self
and
other
) and is used by the
<=
operator.
Read more Tests greater than (for
self
and
other
) and is used by the
>
operator.
Read more Tests greater than or equal to (for
self
and
other
) and is used by
the
>=
operator.
Read more Serialize this value into the given Serde serializer.
Read more Immutably borrows from an owned value.
Read more Mutably borrows from an owned value.
Read more 🔬 This is a nightly-only experimental API. (clone_to_uninit
)
Performs copy-assignment from
self
to
dst
.
Read more Checks if this value is equivalent to the given key.
Read more Returns the argument unchanged.
Calls U::from(self)
.
That is, this conversion is whatever the implementation of
From <T> for U
chooses to do.
The resulting type after obtaining ownership.
Creates owned data from borrowed data, usually by cloning.
Read more Uses borrowed data to replace owned data, usually by cloning.
Read more Converts the given value to a
String
.
Read more The type returned in the event of a conversion error.
Performs the conversion.
The type returned in the event of a conversion error.
Performs the conversion.