1.0.0[−][src]Enum alloc_wg::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; 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
impl<'_, B> Cow<'_, B> where
B: ToOwned + ?Sized,
[src]
B: ToOwned + ?Sized,
pub fn is_borrowed(&self) -> bool
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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());
pub fn is_owned(&self) -> bool
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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());
pub fn to_mut(&mut self) -> &mut <B as ToOwned>::Owned
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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
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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> Add<&'a str> for Cow<'a, str>
1.14.0[src]
type Output = Cow<'a, str>
The resulting type after applying the +
operator.
fn add(self, rhs: &'a str) -> <Cow<'a, str> as Add<&'a str>>::Output
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impl<'a> Add<Cow<'a, str>> for Cow<'a, str>
1.14.0[src]
type Output = Cow<'a, str>
The resulting type after applying the +
operator.
fn add(self, rhs: Cow<'a, str>) -> <Cow<'a, str> as Add<Cow<'a, str>>>::Output
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impl<'a> AddAssign<&'a str> for Cow<'a, str>
1.14.0[src]
fn add_assign(&mut self, rhs: &'a str)
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impl<'a> AddAssign<Cow<'a, str>> for Cow<'a, str>
1.14.0[src]
fn add_assign(&mut self, rhs: Cow<'a, str>)
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impl<'_> AsRef<Path> for Cow<'_, OsStr>
1.8.0[src]
impl<'_, T> AsRef<T> for Cow<'_, T> where
T: ToOwned + ?Sized,
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T: ToOwned + ?Sized,
impl<'a, B> Borrow<B> for Cow<'a, B> where
B: ToOwned + ?Sized,
<B as ToOwned>::Owned: 'a,
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B: ToOwned + ?Sized,
<B as ToOwned>::Owned: 'a,
impl<'_, B> Clone for Cow<'_, B> where
B: ToOwned + ?Sized,
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B: ToOwned + ?Sized,
impl<'_, B> Debug for Cow<'_, B> where
B: Debug + ToOwned + ?Sized,
<B as ToOwned>::Owned: Debug,
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B: Debug + ToOwned + ?Sized,
<B as ToOwned>::Owned: Debug,
impl<'_, B> Default for Cow<'_, B> where
B: ToOwned + ?Sized,
<B as ToOwned>::Owned: Default,
1.11.0[src]
B: ToOwned + ?Sized,
<B as ToOwned>::Owned: Default,
fn default() -> Cow<'_, B>
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Creates an owned Cow<'a, B> with the default value for the contained owned value.
impl<'_, B> Deref for Cow<'_, B> where
B: ToOwned + ?Sized,
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B: ToOwned + ?Sized,
impl<'_, B> Display for Cow<'_, B> where
B: Display + ToOwned + ?Sized,
<B as ToOwned>::Owned: Display,
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B: Display + ToOwned + ?Sized,
<B as ToOwned>::Owned: Display,
impl<'_, B> Eq for Cow<'_, B> where
B: Eq + ToOwned + ?Sized,
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B: Eq + ToOwned + ?Sized,
impl<'a, A> Extend<Cow<'a, str>> for String<A> where
A: AllocRef,
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A: AllocRef,
fn extend<I: IntoIterator<Item = Cow<'a, str>>>(&mut self, iter: I)
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fn extend_one(&mut self, item: A)
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fn extend_reserve(&mut self, additional: usize)
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impl<'a, T> From<&'a [T]> for Cow<'a, [T]> where
T: Clone,
1.8.0[src]
T: Clone,
impl<'a> From<&'a CStr> for Cow<'a, CStr>
1.28.0[src]
impl<'a> From<&'a CString> for Cow<'a, CStr>
1.28.0[src]
impl<'a> From<&'a OsStr> for Cow<'a, OsStr>
1.28.0[src]
impl<'a> From<&'a OsString> for Cow<'a, OsStr>
1.28.0[src]
impl<'a> From<&'a Path> for Cow<'a, Path>
1.6.0[src]
impl<'a> From<&'a PathBuf> for Cow<'a, Path>
1.28.0[src]
impl<'a, A: AllocRef> From<&'a String<A>> for Cow<'a, str>
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impl<'a> From<&'a String> for Cow<'a, str>
1.28.0[src]
impl<'a, T> From<&'a Vec<T>> for Cow<'a, [T]> where
T: Clone,
1.28.0[src]
T: Clone,
impl<'a> From<&'a str> for Cow<'a, str>
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impl<'a> From<CString> for Cow<'a, CStr>
1.28.0[src]
impl<'a, B> From<Cow<'a, B>> for Rc<B> where
B: ToOwned + ?Sized,
Rc<B>: From<&'a B>,
Rc<B>: From<<B as ToOwned>::Owned>,
1.45.0[src]
B: ToOwned + ?Sized,
Rc<B>: From<&'a B>,
Rc<B>: From<<B as ToOwned>::Owned>,
impl<'a, B> From<Cow<'a, B>> for Arc<B> where
B: ToOwned + ?Sized,
Arc<B>: From<&'a B>,
Arc<B>: From<<B as ToOwned>::Owned>,
1.45.0[src]
B: ToOwned + ?Sized,
Arc<B>: From<&'a B>,
Arc<B>: From<<B as ToOwned>::Owned>,
impl<'a> From<Cow<'a, str>> for String
[src]
impl<'a> From<OsString> for Cow<'a, OsStr>
1.28.0[src]
impl<'a> From<PathBuf> for Cow<'a, Path>
1.6.0[src]
impl<'a> From<String> for Cow<'a, str>
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impl<'a, T> From<Vec<T>> for Cow<'a, [T]> where
T: Clone,
1.8.0[src]
T: Clone,
impl<'a, 'b> FromIterator<&'b str> for Cow<'a, str>
1.12.0[src]
impl<'a> FromIterator<Cow<'a, str>> for String
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fn from_iter<I: IntoIterator<Item = Cow<'a, str>>>(iter: I) -> Self
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impl<'a> FromIterator<String> for Cow<'a, str>
1.12.0[src]
impl<'a, T> FromIterator<T> for Cow<'a, [T]> where
T: Clone,
[src]
T: Clone,
impl<'a> FromIterator<char> for Cow<'a, str>
1.12.0[src]
impl<'_, B> Hash for Cow<'_, B> where
B: Hash + ToOwned + ?Sized,
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B: Hash + ToOwned + ?Sized,
fn hash<H>(&self, state: &mut H) where
H: Hasher,
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H: Hasher,
fn hash_slice<H>(data: &[Self], state: &mut H) where
H: Hasher,
1.3.0[src]
H: Hasher,
impl<'_, B> Ord for Cow<'_, B> where
B: Ord + ToOwned + ?Sized,
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B: Ord + ToOwned + ?Sized,
fn cmp(&self, other: &Cow<'_, B>) -> Ordering
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#[must_use]fn max(self, other: Self) -> Self
1.21.0[src]
#[must_use]fn min(self, other: Self) -> Self
1.21.0[src]
#[must_use]fn clamp(self, min: Self, max: Self) -> Self
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impl<'_, '_, A, B> PartialEq<&'_ [B]> for Cow<'_, [A]> where
A: PartialEq<B> + Clone,
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A: PartialEq<B> + Clone,
impl<'_, '_, A, B> PartialEq<&'_ mut [B]> for Cow<'_, [A]> where
A: PartialEq<B> + Clone,
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A: PartialEq<B> + Clone,
impl<'a, 'b> PartialEq<&'a Path> for Cow<'b, OsStr>
1.8.0[src]
impl<'a, 'b> PartialEq<&'b OsStr> for Cow<'a, Path>
1.8.0[src]
impl<'a, 'b> PartialEq<&'b OsStr> for Cow<'a, OsStr>
1.8.0[src]
impl<'a, 'b> PartialEq<&'b Path> for Cow<'a, Path>
1.6.0[src]
impl<'a, 'b> PartialEq<&'b str> for Cow<'a, str>
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impl<A: AllocRef, '_> PartialEq<Cow<'_, str>> for String<A>
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impl<'a, 'b, B, C> PartialEq<Cow<'b, C>> for Cow<'a, B> where
B: PartialEq<C> + ToOwned + ?Sized,
C: ToOwned + ?Sized,
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B: PartialEq<C> + ToOwned + ?Sized,
C: ToOwned + ?Sized,
impl<'a, 'b> PartialEq<OsStr> for Cow<'a, OsStr>
1.8.0[src]
impl<'a, 'b> PartialEq<OsStr> for Cow<'a, Path>
1.8.0[src]
impl<'a, 'b> PartialEq<OsString> for Cow<'a, Path>
1.8.0[src]
impl<'a, 'b> PartialEq<OsString> for Cow<'a, OsStr>
1.8.0[src]
impl<'a, 'b> PartialEq<Path> for Cow<'a, OsStr>
1.8.0[src]
impl<'a, 'b> PartialEq<Path> for Cow<'a, Path>
1.6.0[src]
impl<'a, 'b> PartialEq<PathBuf> for Cow<'a, OsStr>
1.8.0[src]
impl<'a, 'b> PartialEq<PathBuf> for Cow<'a, Path>
1.6.0[src]
impl<A: AllocRef, '_> PartialEq<String<A>> for Cow<'_, str>
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impl<'a, 'b> PartialEq<String> for Cow<'a, str>
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impl<'_, A, B> PartialEq<Vec<B>> for Cow<'_, [A]> where
A: PartialEq<B> + Clone,
[src]
A: PartialEq<B> + Clone,
impl<'a, 'b> PartialEq<str> for Cow<'a, str>
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impl<'a, 'b> PartialOrd<&'a Path> for Cow<'b, OsStr>
1.8.0[src]
fn partial_cmp(&self, other: &&'a Path) -> Option<Ordering>
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#[must_use]fn lt(&self, other: &Rhs) -> bool
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#[must_use]fn le(&self, other: &Rhs) -> bool
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#[must_use]fn gt(&self, other: &Rhs) -> bool
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#[must_use]fn ge(&self, other: &Rhs) -> bool
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impl<'a, 'b> PartialOrd<&'b OsStr> for Cow<'a, OsStr>
1.8.0[src]
fn partial_cmp(&self, other: &&'b OsStr) -> Option<Ordering>
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#[must_use]fn lt(&self, other: &Rhs) -> bool
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#[must_use]fn le(&self, other: &Rhs) -> bool
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#[must_use]fn gt(&self, other: &Rhs) -> bool
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#[must_use]fn ge(&self, other: &Rhs) -> bool
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impl<'a, 'b> PartialOrd<&'b OsStr> for Cow<'a, Path>
1.8.0[src]
fn partial_cmp(&self, other: &&'b OsStr) -> Option<Ordering>
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#[must_use]fn lt(&self, other: &Rhs) -> bool
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#[must_use]fn le(&self, other: &Rhs) -> bool
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#[must_use]fn gt(&self, other: &Rhs) -> bool
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#[must_use]fn ge(&self, other: &Rhs) -> bool
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impl<'a, 'b> PartialOrd<&'b Path> for Cow<'a, Path>
1.8.0[src]
fn partial_cmp(&self, other: &&'b Path) -> Option<Ordering>
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#[must_use]fn lt(&self, other: &Rhs) -> bool
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#[must_use]fn le(&self, other: &Rhs) -> bool
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#[must_use]fn gt(&self, other: &Rhs) -> bool
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#[must_use]fn ge(&self, other: &Rhs) -> bool
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impl<'a, B> PartialOrd<Cow<'a, B>> for Cow<'a, B> where
B: PartialOrd<B> + ToOwned + ?Sized,
[src]
B: PartialOrd<B> + ToOwned + ?Sized,
fn partial_cmp(&self, other: &Cow<'a, B>) -> Option<Ordering>
[src]
#[must_use]fn lt(&self, other: &Rhs) -> bool
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#[must_use]fn le(&self, other: &Rhs) -> bool
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#[must_use]fn gt(&self, other: &Rhs) -> bool
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#[must_use]fn ge(&self, other: &Rhs) -> bool
[src]
impl<'a, 'b> PartialOrd<OsStr> for Cow<'a, Path>
1.8.0[src]
fn partial_cmp(&self, other: &OsStr) -> Option<Ordering>
[src]
#[must_use]fn lt(&self, other: &Rhs) -> bool
[src]
#[must_use]fn le(&self, other: &Rhs) -> bool
[src]
#[must_use]fn gt(&self, other: &Rhs) -> bool
[src]
#[must_use]fn ge(&self, other: &Rhs) -> bool
[src]
impl<'a, 'b> PartialOrd<OsStr> for Cow<'a, OsStr>
1.8.0[src]
fn partial_cmp(&self, other: &OsStr) -> Option<Ordering>
[src]
#[must_use]fn lt(&self, other: &Rhs) -> bool
[src]
#[must_use]fn le(&self, other: &Rhs) -> bool
[src]
#[must_use]fn gt(&self, other: &Rhs) -> bool
[src]
#[must_use]fn ge(&self, other: &Rhs) -> bool
[src]
impl<'a, 'b> PartialOrd<OsString> for Cow<'a, Path>
1.8.0[src]
fn partial_cmp(&self, other: &OsString) -> Option<Ordering>
[src]
#[must_use]fn lt(&self, other: &Rhs) -> bool
[src]
#[must_use]fn le(&self, other: &Rhs) -> bool
[src]
#[must_use]fn gt(&self, other: &Rhs) -> bool
[src]
#[must_use]fn ge(&self, other: &Rhs) -> bool
[src]
impl<'a, 'b> PartialOrd<OsString> for Cow<'a, OsStr>
1.8.0[src]
fn partial_cmp(&self, other: &OsString) -> Option<Ordering>
[src]
#[must_use]fn lt(&self, other: &Rhs) -> bool
[src]
#[must_use]fn le(&self, other: &Rhs) -> bool
[src]
#[must_use]fn gt(&self, other: &Rhs) -> bool
[src]
#[must_use]fn ge(&self, other: &Rhs) -> bool
[src]
impl<'a, 'b> PartialOrd<Path> for Cow<'a, Path>
1.8.0[src]
fn partial_cmp(&self, other: &Path) -> Option<Ordering>
[src]
#[must_use]fn lt(&self, other: &Rhs) -> bool
[src]
#[must_use]fn le(&self, other: &Rhs) -> bool
[src]
#[must_use]fn gt(&self, other: &Rhs) -> bool
[src]
#[must_use]fn ge(&self, other: &Rhs) -> bool
[src]
impl<'a, 'b> PartialOrd<Path> for Cow<'a, OsStr>
1.8.0[src]
fn partial_cmp(&self, other: &Path) -> Option<Ordering>
[src]
#[must_use]fn lt(&self, other: &Rhs) -> bool
[src]
#[must_use]fn le(&self, other: &Rhs) -> bool
[src]
#[must_use]fn gt(&self, other: &Rhs) -> bool
[src]
#[must_use]fn ge(&self, other: &Rhs) -> bool
[src]
impl<'a, 'b> PartialOrd<PathBuf> for Cow<'a, Path>
1.8.0[src]
fn partial_cmp(&self, other: &PathBuf) -> Option<Ordering>
[src]
#[must_use]fn lt(&self, other: &Rhs) -> bool
[src]
#[must_use]fn le(&self, other: &Rhs) -> bool
[src]
#[must_use]fn gt(&self, other: &Rhs) -> bool
[src]
#[must_use]fn ge(&self, other: &Rhs) -> bool
[src]
impl<'a, 'b> PartialOrd<PathBuf> for Cow<'a, OsStr>
1.8.0[src]
fn partial_cmp(&self, other: &PathBuf) -> Option<Ordering>
[src]
#[must_use]fn lt(&self, other: &Rhs) -> bool
[src]
#[must_use]fn le(&self, other: &Rhs) -> bool
[src]
#[must_use]fn gt(&self, other: &Rhs) -> bool
[src]
#[must_use]fn ge(&self, other: &Rhs) -> bool
[src]
impl<'_> ToString for Cow<'_, str>
1.17.0[src]
impl<'a, A: AllocRef> TryExtend<Cow<'a, str>> for String<A>
[src]
type Err = TryReserveError
fn try_extend<I: IntoIterator<Item = Cow<'a, str>>>(
&mut self,
iter: I
) -> Result<(), Self::Err>
[src]
&mut self,
iter: I
) -> Result<(), Self::Err>
Auto Trait Implementations
impl<'a, B: ?Sized> RefUnwindSafe for Cow<'a, B> where
B: RefUnwindSafe,
<B as ToOwned>::Owned: RefUnwindSafe,
B: RefUnwindSafe,
<B as ToOwned>::Owned: RefUnwindSafe,
impl<'a, B: ?Sized> Send for Cow<'a, B> where
B: Sync,
<B as ToOwned>::Owned: Send,
B: Sync,
<B as ToOwned>::Owned: Send,
impl<'a, B: ?Sized> Sync for Cow<'a, B> where
B: Sync,
<B as ToOwned>::Owned: Sync,
B: Sync,
<B as ToOwned>::Owned: Sync,
impl<'a, B: ?Sized> Unpin for Cow<'a, B> where
<B as ToOwned>::Owned: Unpin,
<B as ToOwned>::Owned: Unpin,
impl<'a, B: ?Sized> UnwindSafe for Cow<'a, B> where
B: RefUnwindSafe,
<B as ToOwned>::Owned: UnwindSafe,
B: RefUnwindSafe,
<B as ToOwned>::Owned: UnwindSafe,
Blanket Implementations
impl<T> Any for T where
T: 'static + ?Sized,
[src]
T: 'static + ?Sized,
impl<T> Borrow<T> for T where
T: ?Sized,
[src]
T: ?Sized,
impl<T> BorrowMut<T> for T where
T: ?Sized,
[src]
T: ?Sized,
fn borrow_mut(&mut self) -> &mut T
[src]
impl<T> From<T> for T
[src]
impl<T, U> Into<U> for T where
U: From<T>,
[src]
U: From<T>,
impl<T> ToOwned for T where
T: Clone,
[src]
T: Clone,
type Owned = T
The resulting type after obtaining ownership.
fn to_owned(&self) -> T
[src]
fn clone_into(&self, target: &mut T)
[src]
impl<T> ToString for T where
T: Display + ?Sized,
[src]
T: Display + ?Sized,
impl<T, U> TryFrom<U> for T where
U: Into<T>,
[src]
U: Into<T>,
type Error = Infallible
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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impl<T, U> TryInto<U> for T where
U: TryFrom<T>,
[src]
U: TryFrom<T>,