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, 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 } } } // 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<'a, B: ?Sized> Cow<'a, B> where
B: ToOwned,
[src]
impl<'a, B: ?Sized> Cow<'a, B> where
B: ToOwned,
pub fn to_mut(&mut self) -> &mut <B as ToOwned>::Owned
[src]
pub fn to_mut(&mut self) -> &mut <B as ToOwned>::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> );
pub fn into_owned(self) -> <B as ToOwned>::Owned
[src]
pub fn into_owned(self) -> <B as ToOwned>::Owned
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<'a> ToString for Cow<'a, str>
1.17.0[src]
impl<'a> ToString for Cow<'a, str>
impl<'a, 'b, B: ?Sized, C: ?Sized> PartialEq<Cow<'b, C>> for Cow<'a, B> where
B: PartialEq<C> + ToOwned,
C: ToOwned,
[src]
impl<'a, 'b, B: ?Sized, C: ?Sized> PartialEq<Cow<'b, C>> for Cow<'a, B> where
B: PartialEq<C> + ToOwned,
C: ToOwned,
fn eq(&self, other: &Cow<'b, C>) -> bool
[src]
fn eq(&self, other: &Cow<'b, C>) -> bool
This method tests for self
and other
values to be equal, and is used by ==
. Read more
#[must_use]
fn ne(&self, other: &Rhs) -> bool
[src]
#[must_use]
fn ne(&self, other: &Rhs) -> bool
This method tests for !=
.
impl<'a, 'b> PartialEq<str> for Cow<'a, str>
[src]
impl<'a, 'b> PartialEq<str> for Cow<'a, str>
fn eq(&self, other: &str) -> bool
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fn eq(&self, other: &str) -> bool
This method tests for self
and other
values to be equal, and is used by ==
. Read more
fn ne(&self, other: &str) -> bool
[src]
fn ne(&self, other: &str) -> bool
This method tests for !=
.
impl<'a, 'b> PartialEq<Cow<'a, str>> for str
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impl<'a, 'b> PartialEq<Cow<'a, str>> for str
fn eq(&self, other: &Cow<'a, str>) -> bool
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fn eq(&self, other: &Cow<'a, str>) -> bool
This method tests for self
and other
values to be equal, and is used by ==
. Read more
fn ne(&self, other: &Cow<'a, str>) -> bool
[src]
fn ne(&self, other: &Cow<'a, str>) -> bool
This method tests for !=
.
impl<'a, 'b> PartialEq<&'b str> for Cow<'a, str>
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impl<'a, 'b> PartialEq<&'b str> for Cow<'a, str>
fn eq(&self, other: &&'b str) -> bool
[src]
fn eq(&self, other: &&'b str) -> bool
This method tests for self
and other
values to be equal, and is used by ==
. Read more
fn ne(&self, other: &&'b str) -> bool
[src]
fn ne(&self, other: &&'b str) -> bool
This method tests for !=
.
impl<'a, 'b> PartialEq<Cow<'a, str>> for &'b str
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impl<'a, 'b> PartialEq<Cow<'a, str>> for &'b str
fn eq(&self, other: &Cow<'a, str>) -> bool
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fn eq(&self, other: &Cow<'a, str>) -> bool
This method tests for self
and other
values to be equal, and is used by ==
. Read more
fn ne(&self, other: &Cow<'a, str>) -> bool
[src]
fn ne(&self, other: &Cow<'a, str>) -> bool
This method tests for !=
.
impl<'a, 'b> PartialEq<String> for Cow<'a, str>
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impl<'a, 'b> PartialEq<String> for Cow<'a, str>
fn eq(&self, other: &String) -> bool
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fn eq(&self, other: &String) -> bool
This method tests for self
and other
values to be equal, and is used by ==
. Read more
fn ne(&self, other: &String) -> bool
[src]
fn ne(&self, other: &String) -> bool
This method tests for !=
.
impl<'a, 'b> PartialEq<Cow<'a, str>> for String
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impl<'a, 'b> PartialEq<Cow<'a, str>> for String
fn eq(&self, other: &Cow<'a, str>) -> bool
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fn eq(&self, other: &Cow<'a, str>) -> bool
This method tests for self
and other
values to be equal, and is used by ==
. Read more
fn ne(&self, other: &Cow<'a, str>) -> bool
[src]
fn ne(&self, other: &Cow<'a, str>) -> bool
This method tests for !=
.
impl<'a, 'b, A: Clone, B> PartialEq<&'b [B]> for Cow<'a, [A]> where
A: PartialEq<B>,
[src]
impl<'a, 'b, A: Clone, B> PartialEq<&'b [B]> for Cow<'a, [A]> where
A: PartialEq<B>,
fn eq(&self, other: &&'b [B]) -> bool
[src]
fn eq(&self, other: &&'b [B]) -> bool
This method tests for self
and other
values to be equal, and is used by ==
. Read more
fn ne(&self, other: &&'b [B]) -> bool
[src]
fn ne(&self, other: &&'b [B]) -> bool
This method tests for !=
.
impl<'a, 'b, A: Clone, B> PartialEq<&'b mut [B]> for Cow<'a, [A]> where
A: PartialEq<B>,
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impl<'a, 'b, A: Clone, B> PartialEq<&'b mut [B]> for Cow<'a, [A]> where
A: PartialEq<B>,
fn eq(&self, other: &&'b mut [B]) -> bool
[src]
fn eq(&self, other: &&'b mut [B]) -> bool
This method tests for self
and other
values to be equal, and is used by ==
. Read more
fn ne(&self, other: &&'b mut [B]) -> bool
[src]
fn ne(&self, other: &&'b mut [B]) -> bool
This method tests for !=
.
impl<'a, 'b, A: Clone, B> PartialEq<Vec<B>> for Cow<'a, [A]> where
A: PartialEq<B>,
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impl<'a, 'b, A: Clone, B> PartialEq<Vec<B>> for Cow<'a, [A]> where
A: PartialEq<B>,
fn eq(&self, other: &Vec<B>) -> bool
[src]
fn eq(&self, other: &Vec<B>) -> bool
This method tests for self
and other
values to be equal, and is used by ==
. Read more
fn ne(&self, other: &Vec<B>) -> bool
[src]
fn ne(&self, other: &Vec<B>) -> bool
This method tests for !=
.
impl<'a, B: ?Sized> Eq for Cow<'a, B> where
B: Eq + ToOwned,
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impl<'a, B: ?Sized> Eq for Cow<'a, B> where
B: Eq + ToOwned,
impl<'a, B: ?Sized> Ord for Cow<'a, B> where
B: Ord + ToOwned,
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impl<'a, B: ?Sized> Ord for Cow<'a, B> where
B: Ord + ToOwned,
fn cmp(&self, other: &Cow<'a, B>) -> Ordering
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fn cmp(&self, other: &Cow<'a, B>) -> Ordering
This method returns an Ordering
between self
and other
. Read more
fn max(self, other: Self) -> Self
1.21.0[src]
fn max(self, other: Self) -> Self
Compares and returns the maximum of two values. Read more
fn min(self, other: Self) -> Self
1.21.0[src]
fn min(self, other: Self) -> Self
Compares and returns the minimum of two values. Read more
impl<'a, B: ?Sized> PartialOrd<Cow<'a, B>> for Cow<'a, B> where
B: PartialOrd + ToOwned,
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impl<'a, B: ?Sized> PartialOrd<Cow<'a, B>> for Cow<'a, B> where
B: PartialOrd + ToOwned,
fn partial_cmp(&self, other: &Cow<'a, B>) -> Option<Ordering>
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fn partial_cmp(&self, other: &Cow<'a, B>) -> Option<Ordering>
This method returns an ordering between self
and other
values if one exists. Read more
#[must_use]
fn lt(&self, other: &Rhs) -> bool
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#[must_use]
fn lt(&self, other: &Rhs) -> bool
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
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#[must_use]
fn le(&self, other: &Rhs) -> bool
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
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#[must_use]
fn gt(&self, other: &Rhs) -> bool
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
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#[must_use]
fn ge(&self, other: &Rhs) -> bool
This method tests greater than or equal to (for self
and other
) and is used by the >=
operator. Read more
impl<'a, B: ?Sized> Display for Cow<'a, B> where
B: Display + ToOwned,
<B as ToOwned>::Owned: Display,
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impl<'a, B: ?Sized> Display for Cow<'a, B> where
B: Display + ToOwned,
<B as ToOwned>::Owned: Display,
fn fmt(&self, f: &mut Formatter) -> Result
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fn fmt(&self, f: &mut Formatter) -> Result
Formats the value using the given formatter. Read more
impl<'a, B: ?Sized> Debug for Cow<'a, B> where
B: Debug + ToOwned,
<B as ToOwned>::Owned: Debug,
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impl<'a, B: ?Sized> Debug for Cow<'a, B> where
B: Debug + ToOwned,
<B as ToOwned>::Owned: Debug,
fn fmt(&self, f: &mut Formatter) -> Result
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fn fmt(&self, f: &mut Formatter) -> Result
Formats the value using the given formatter. Read more
impl<'a> Add<&'a str> for Cow<'a, str>
1.14.0[src]
impl<'a> Add<&'a str> for Cow<'a, str>
type Output = Cow<'a, str>
The resulting type after applying the +
operator.
fn add(self, rhs: &'a str) -> Self::Output
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fn add(self, rhs: &'a str) -> Self::Output
Performs the +
operation.
impl<'a> Add<Cow<'a, str>> for Cow<'a, str>
1.14.0[src]
impl<'a> Add<Cow<'a, str>> for Cow<'a, str>
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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fn add(self, rhs: Cow<'a, str>) -> Self::Output
Performs the +
operation.
impl<'a> AddAssign<&'a str> for Cow<'a, str>
1.14.0[src]
impl<'a> AddAssign<&'a str> for Cow<'a, str>
fn add_assign(&mut self, rhs: &'a str)
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fn add_assign(&mut self, rhs: &'a str)
Performs the +=
operation.
impl<'a> AddAssign<Cow<'a, str>> for Cow<'a, str>
1.14.0[src]
impl<'a> AddAssign<Cow<'a, str>> for Cow<'a, str>
fn add_assign(&mut self, rhs: Cow<'a, str>)
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fn add_assign(&mut self, rhs: Cow<'a, str>)
Performs the +=
operation.
impl<'a, B: ?Sized> Deref for Cow<'a, B> where
B: ToOwned,
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impl<'a, B: ?Sized> Deref for Cow<'a, B> where
B: ToOwned,
type Target = B
The resulting type after dereferencing.
fn deref(&self) -> &B
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fn deref(&self) -> &B
Dereferences the value.
impl<'a, B: ?Sized> Hash for Cow<'a, B> where
B: Hash + ToOwned,
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impl<'a, B: ?Sized> Hash for Cow<'a, B> where
B: Hash + ToOwned,
fn hash<H: Hasher>(&self, state: &mut H)
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fn hash<H: Hasher>(&self, state: &mut H)
Feeds this value into the given [Hasher
]. Read more
fn hash_slice<H>(data: &[Self], state: &mut H) where
H: Hasher,
1.3.0[src]
fn hash_slice<H>(data: &[Self], state: &mut H) where
H: Hasher,
Feeds a slice of this type into the given [Hasher
]. Read more
impl<'a> FromIterator<Cow<'a, str>> for String
1.19.0[src]
impl<'a> FromIterator<Cow<'a, str>> for String
fn from_iter<I: IntoIterator<Item = Cow<'a, str>>>(iter: I) -> String
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fn from_iter<I: IntoIterator<Item = Cow<'a, str>>>(iter: I) -> String
Creates a value from an iterator. Read more
impl<'a> FromIterator<char> for Cow<'a, str>
1.12.0[src]
impl<'a> FromIterator<char> for Cow<'a, str>
fn from_iter<I: IntoIterator<Item = char>>(it: I) -> Cow<'a, str>
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fn from_iter<I: IntoIterator<Item = char>>(it: I) -> Cow<'a, str>
Creates a value from an iterator. Read more
impl<'a, 'b> FromIterator<&'b str> for Cow<'a, str>
1.12.0[src]
impl<'a, 'b> FromIterator<&'b str> for Cow<'a, str>
fn from_iter<I: IntoIterator<Item = &'b str>>(it: I) -> Cow<'a, str>
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fn from_iter<I: IntoIterator<Item = &'b str>>(it: I) -> Cow<'a, str>
Creates a value from an iterator. Read more
impl<'a> FromIterator<String> for Cow<'a, str>
1.12.0[src]
impl<'a> FromIterator<String> for Cow<'a, str>
fn from_iter<I: IntoIterator<Item = String>>(it: I) -> Cow<'a, str>
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fn from_iter<I: IntoIterator<Item = String>>(it: I) -> Cow<'a, str>
Creates a value from an iterator. Read more
impl<'a, T> FromIterator<T> for Cow<'a, [T]> where
T: Clone,
[src]
impl<'a, T> FromIterator<T> for Cow<'a, [T]> where
T: Clone,
fn from_iter<I: IntoIterator<Item = T>>(it: I) -> Cow<'a, [T]>
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fn from_iter<I: IntoIterator<Item = T>>(it: I) -> Cow<'a, [T]>
Creates a value from an iterator. Read more
impl<'a> Extend<Cow<'a, str>> for String
1.19.0[src]
impl<'a> Extend<Cow<'a, str>> for String
fn extend<I: IntoIterator<Item = Cow<'a, str>>>(&mut self, iter: I)
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fn extend<I: IntoIterator<Item = Cow<'a, str>>>(&mut self, iter: I)
Extends a collection with the contents of an iterator. Read more
impl<'a> From<Cow<'a, str>> for String
1.14.0[src]
impl<'a> From<Cow<'a, str>> for String
impl<'a> From<&'a str> for Cow<'a, str>
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impl<'a> From<&'a str> for Cow<'a, str>
impl<'a> From<String> for Cow<'a, str>
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impl<'a> From<String> for Cow<'a, str>
impl<'a> From<&'a String> for Cow<'a, str>
1.28.0[src]
impl<'a> From<&'a String> for Cow<'a, str>
impl<'a, T> From<Cow<'a, [T]>> for Vec<T> where
[T]: ToOwned<Owned = Vec<T>>,
1.14.0[src]
impl<'a, T> From<Cow<'a, [T]>> for Vec<T> where
[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<&'a [T]> for Cow<'a, [T]>
impl<'a, T: Clone> From<Vec<T>> for Cow<'a, [T]>
1.8.0[src]
impl<'a, T: Clone> From<Vec<T>> for Cow<'a, [T]>
impl<'a, T: Clone> From<&'a Vec<T>> for Cow<'a, [T]>
1.28.0[src]
impl<'a, T: Clone> From<&'a Vec<T>> for Cow<'a, [T]>
impl<'a, B: ?Sized> Clone for Cow<'a, B> where
B: ToOwned,
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impl<'a, B: ?Sized> Clone for Cow<'a, B> where
B: ToOwned,
fn clone(&self) -> Cow<'a, B>
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fn clone(&self) -> Cow<'a, B>
Returns a copy of the value. Read more
fn clone_from(&mut self, source: &Cow<'a, B>)
[src]
fn clone_from(&mut self, source: &Cow<'a, B>)
Performs copy-assignment from source
. Read more
impl<'a, T: ?Sized + ToOwned> AsRef<T> for Cow<'a, T>
[src]
impl<'a, T: ?Sized + ToOwned> AsRef<T> for Cow<'a, T>
impl<'a, B: ?Sized> Default for Cow<'a, B> where
B: ToOwned,
<B as ToOwned>::Owned: Default,
1.11.0[src]
impl<'a, B: ?Sized> Default for Cow<'a, B> where
B: ToOwned,
<B as ToOwned>::Owned: Default,
fn default() -> Cow<'a, B>
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fn default() -> Cow<'a, B>
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]
impl<'a, B: ?Sized> Borrow<B> for Cow<'a, B> where
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,
impl<'a, B: ?Sized> Send for Cow<'a, B> where
B: Sync,
<B as ToOwned>::Owned: Send,
impl<'a, B: ?Sized> Sync for Cow<'a, B> where
B: Sync,
<B as ToOwned>::Owned: Sync,
impl<'a, B: ?Sized> Sync for Cow<'a, B> where
B: Sync,
<B as ToOwned>::Owned: Sync,
Blanket Implementations
impl<T> ToOwned for T where
T: Clone,
[src]
impl<T> ToOwned for T where
T: Clone,
type Owned = T
fn to_owned(&Self) -> T
[src]
fn to_owned(&Self) -> T
Creates owned data from borrowed data, usually by cloning. Read more
fn clone_into(&Self, &mut T)
[src]
fn clone_into(&Self, &mut T)
🔬 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
impl<T> ToString for T where
T: Display + ?Sized,
[src]
impl<T> ToString for T where
T: Display + ?Sized,
impl<T, U> TryFrom for T where
T: From<U>,
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impl<T, U> TryFrom for T where
T: From<U>,
type Error = !
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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fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>
Performs the conversion.
impl<T> From for T
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impl<T> From for T
impl<T, U> TryInto for T where
U: TryFrom<T>,
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impl<T, U> TryInto for T where
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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fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>
Performs the conversion.
impl<T, U> Into for T where
U: From<T>,
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impl<T, U> Into for T where
U: From<T>,
impl<T> Borrow for T where
T: ?Sized,
[src]
impl<T> Borrow for T where
T: ?Sized,
impl<T> BorrowMut for T where
T: ?Sized,
[src]
impl<T> BorrowMut for T where
T: ?Sized,
fn borrow_mut(&mut self) -> &mut T
[src]
fn borrow_mut(&mut self) -> &mut T
Mutably borrows from an owned value. Read more
impl<T> Any for T where
T: 'static + ?Sized,
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impl<T> Any for T where
T: 'static + ?Sized,
fn get_type_id(&self) -> TypeId
[src]
fn get_type_id(&self) -> TypeId
🔬 This is a nightly-only experimental API. (get_type_id
#27745)
this method will likely be replaced by an associated static
Gets the TypeId
of self
. Read more