Cow in alloc::borrow - Rust
Description: A clone-on-write smart pointer.

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## Cow

# Enum Cow

1.36.0 · Source

    pub enum Cow<'a, B>where
        B: ToOwned + ?Sized + 'a,{
        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> 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's check it out.
    match clone_on_write {
        Items { values: Cow::Owned(_) } => println!("clone_on_write contains owned data"),
        _ => panic!("expect owned data"),
    }

## Variants§

§1.36.0

### Borrowed(&'a B)

Borrowed data.

§1.36.0

### Owned(<B as ToOwned>::Owned)

Owned data.

## Implementations§

Source§

### impl<B: ?Sized + ToOwned> Cow<'_, B>

Source

#### pub const fn is_borrowed(c: &Self) -> bool

🔬This is a nightly-only experimental API. (`cow_is_borrowed` #65143)

Returns true if the data is borrowed, i.e. if `to_mut` would require additional work.

Note: this is an associated function, which means that you have to call it as `Cow::is_borrowed(&c)` instead of `c.is_borrowed()`. This is so that there is no conflict with a method on the inner type.

##### §Examples

    #![feature(cow_is_borrowed)]
    use std::borrow::Cow;

    let cow = Cow::Borrowed("moo");
    assert!(Cow::is_borrowed(&cow));

    let bull: Cow<'_, str> = Cow::Owned("...moo?".to_string());
    assert!(!Cow::is_borrowed(&bull));

Source

#### pub const fn is_owned(c: &Self) -> bool

🔬This is a nightly-only experimental API. (`cow_is_borrowed` #65143)

Returns true if the data is owned, i.e. if `to_mut` would be a no-op.

Note: this is an associated function, which means that you have to call it as `Cow::is_owned(&c)` instead of `c.is_owned()`. This is so that there is no conflict with a method on the inner type.

##### §Examples

    #![feature(cow_is_borrowed)]
    use std::borrow::Cow;

    let cow: Cow<'_, str> = Cow::Owned("moo".to_string());
    assert!(Cow::is_owned(&cow));

    let bull = Cow::Borrowed("...moo?");
    assert!(!Cow::is_owned(&bull));

1.0.0 · Source

#### 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>
    );

1.0.0 · Source

#### 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` 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)
    );

## Trait Implementations§

1.14.0 · Source§

### impl<'a> Add<&'a str> for Cow<'a, str>

Source§

#### type Output = Cow<'a, str>

The resulting type after applying the `+` operator.
Source§

#### fn add(self, rhs: &'a str) -> Self::Output

Performs the `+` operation. Read more
1.14.0 · Source§

### impl<'a> Add for Cow<'a, str>

Source§

#### type Output = Cow<'a, str>

The resulting type after applying the `+` operator.
Source§

#### fn add(self, rhs: Cow<'a, str>) -> Self::Output

Performs the `+` operation. Read more
1.14.0 · Source§

### impl<'a> AddAssign<&'a str> for Cow<'a, str>

Source§

#### fn add_assign(&mut self, rhs: &'a str)

Performs the `+=` operation. Read more
1.14.0 · Source§

### impl<'a> AddAssign for Cow<'a, str>

Source§

#### fn add_assign(&mut self, rhs: Cow<'a, str>)

Performs the `+=` operation. Read more
1.0.0 · Source§

### impl<T: ?Sized + ToOwned> AsRef<T> for Cow<'_, T>

Source§

#### fn as_ref(&self) -> &T

Converts this type into a shared reference of the (usually inferred) input type.
1.0.0 · Source§

### impl<'a, B: ?Sized + ToOwned> Borrow<B> for Cow<'a, B>

Source§

#### fn borrow(&self) -> &B

Immutably borrows from an owned value. Read more
1.0.0 · Source§

### impl<B: ?Sized + ToOwned> Clone for Cow<'_, B>

Source§

#### fn clone(&self) -> Self

Returns a duplicate of the value. Read more
Source§

#### fn clone_from(&mut self, source: &Self)

Performs copy-assignment from `source`. Read more
1.0.0 · Source§

### impl<B> Debug for Cow<'_, B>
where B: Debug + ToOwned<Owned: Debug> + ?Sized,

Source§

#### fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter. Read more
1.11.0 · Source§

### impl<B> Default for Cow<'_, B>
where B: ToOwned<Owned: Default> + ?Sized,

Source§

#### fn default() -> Self

Creates an owned Cow<’a, B> with the default value for the contained owned value.

1.0.0 · Source§

### impl<B: ?Sized + ToOwned> Deref for Cow<'_, B>

Source§

#### type Target = B

The resulting type after dereferencing.
Source§

#### fn deref(&self) -> &B

Dereferences the value.
1.0.0 · Source§

### impl<B> Display for Cow<'_, B>
where B: Display + ToOwned<Owned: Display> + ?Sized,

Source§

#### fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter. Read more
1.19.0 · Source§

### impl<'a> Extend<Cow<'a, str>> for String

Source§

#### fn extend<I: IntoIterator<Item = Cow<'a, str>>>(&mut self, iter: I)

Extends a collection with the contents of an iterator. Read more
Source§

#### fn extend_one(&mut self, s: Cow<'a, str>)

🔬This is a nightly-only experimental API. (`extend_one` #72631)
Extends a collection with exactly one element.
Source§

#### fn extend_reserve(&mut self, additional: usize)

🔬This is a nightly-only experimental API. (`extend_one` #72631)
Reserves capacity in a collection for the given number of additional elements. Read more
1.8.0 · Source§

### impl<'a, T: Clone> From<&'a [T]> for Cow<'a, [T]>

Source§

#### fn from(s: &'a [T]) -> Cow<'a, [T]>

Creates a `Borrowed` variant of `Cow` from a slice.

This conversion does not allocate or clone the data.

1.77.0 · Source§

### impl<'a, T: Clone, const N: usize> From<&'a [T; N]> for Cow<'a, [T]>

Source§

#### fn from(s: &'a [T; N]) -> Cow<'a, [T]>

Creates a `Borrowed` variant of `Cow` from a reference to an array.

This conversion does not allocate or clone the data.

Source§

### impl<'a> From<&'a ByteStr> for Cow<'a, ByteStr>

Source§

#### fn from(s: &'a ByteStr) -> Self

Converts to this type from the input type.
Source§

### impl<'a> From<&'a ByteString> for Cow<'a, ByteStr>

Source§

#### fn from(s: &'a ByteString) -> Self

Converts to this type from the input type.
1.28.0 · Source§

### impl<'a> From<&'a CStr> for Cow<'a, CStr>

Source§

#### fn from(s: &'a CStr) -> Cow<'a, CStr>

Converts a `CStr` into a borrowed `Cow` without copying or allocating.

1.28.0 · Source§

### impl<'a> From<&'a CString> for Cow<'a, CStr>

Source§

#### fn from(s: &'a CString) -> Cow<'a, CStr>

Converts a `&``CString` into a borrowed `Cow` without copying or allocating.

1.28.0 · Source§

### impl<'a> From<&'a String> for Cow<'a, str>

Source§

#### fn from(s: &'a String) -> Cow<'a, str>

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"));

1.28.0 · Source§

### impl<'a, T: Clone> From<&'a Vec<T>> for Cow<'a, [T]>

Source§

#### fn from(v: &'a Vec<T>) -> Cow<'a, [T]>

Creates a `Borrowed` variant of `Cow` from a reference to `Vec`.

This conversion does not allocate or clone the data.

1.0.0 · Source§

### impl<'a> From<&'a str> for Cow<'a, str>

Source§

#### fn from(s: &'a str) -> Cow<'a, str>

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"));

Source§

### impl<'a> From<ByteString> for Cow<'a, ByteStr>

Source§

#### fn from(s: ByteString) -> Self

Converts to this type from the input type.
1.28.0 · Source§

### impl<'a> From<CString> for Cow<'a, CStr>

Source§

#### fn from(s: CString) -> Cow<'a, CStr>

Converts a `CString` into an owned `Cow` without copying or allocating.

1.45.0 · Source§

### impl<T: Clone> From<Cow<'_, [T]>> for Box<[T]>

Source§

#### fn from(cow: Cow<'_, [T]>) -> Box<[T]>

Converts a `Cow<'_, [T]>` into a `Box<[T]>`

When `cow` is the `Cow::Borrowed` variant, this conversion allocates on the heap and copies the underlying slice. Otherwise, it will try to reuse the owned `Vec`’s allocation.

1.45.0 · Source§

### impl From<Cow<'_, CStr>> for Box<CStr>

Source§

#### fn from(cow: Cow<'_, CStr>) -> Box<CStr>

Converts a `Cow<'a, CStr>` into a `Box<CStr>`, by copying the contents if they are borrowed.

1.45.0 · Source§

### impl From<Cow<'_, str>> for Box<str>

Source§

#### fn from(cow: Cow<'_, str>) -> Box<str>

Converts a `Cow<'_, str>` into a `Box<str>`

When `cow` is the `Cow::Borrowed` variant, this conversion allocates on the heap and copies the underlying `str`. Otherwise, it will try to reuse the owned `String`’s allocation.

##### §Examples

    use std::borrow::Cow;

    let unboxed = Cow::Borrowed("hello");
    let boxed: Box<str> = Box::from(unboxed);
    println!("{boxed}");

    let unboxed = Cow::Owned("hello".to_string());
    let boxed: Box<str> = Box::from(unboxed);
    println!("{boxed}");

1.14.0 · Source§

### impl<'a, T> From<Cow<'a, [T]>> for Vec<T>
where [T]: ToOwned<Owned = Vec<T>>,

Source§

#### fn from(s: Cow<'a, [T]>) -> Vec<T>

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));

1.45.0 · Source§

### impl<'a, B> From<Cow<'a, B>> for Arc<B>
where B: ToOwned + ?Sized, Arc<B>: From<&'a B> + From<B::Owned>,

Source§

#### fn from(cow: Cow<'a, B>) -> Arc<B>

Creates an atomically reference-counted pointer from a clone-on-write pointer by copying its content.

##### §Example

    let cow: Cow<'_, str> = Cow::Borrowed("eggplant");
    let shared: Arc<str> = Arc::from(cow);
    assert_eq!("eggplant", &shared[..]);

1.45.0 · Source§

### impl<'a, B> From<Cow<'a, B>> for Rc<B>
where B: ToOwned + ?Sized, Rc<B>: From<&'a B> + From<B::Owned>,

Source§

#### fn from(cow: Cow<'a, B>) -> Rc<B>

Creates a reference-counted pointer from a clone-on-write pointer by copying its content.

##### §Example

    let cow: Cow<'_, str> = Cow::Borrowed("eggplant");
    let shared: Rc<str> = Rc::from(cow);
    assert_eq!("eggplant", &shared[..]);

1.28.0 · Source§

### impl<'a> From<Cow<'a, CStr>> for CString

Source§

#### fn from(s: Cow<'a, CStr>) -> Self

Converts a `Cow<'a, CStr>` into a `CString`, by copying the contents if they are borrowed.

1.14.0 · Source§

### impl<'a> From<Cow<'a, str>> for String

Source§

#### fn from(s: Cow<'a, str>) -> String

Converts a clone-on-write string to an owned instance of `String`.

This extracts the owned string, clones the string if it is not already owned.

##### §Example

    // If the string is not owned...
    let cow: Cow<'_, str> = Cow::Borrowed("eggplant");
    // It will allocate on the heap and copy the string.
    let owned: String = String::from(cow);
    assert_eq!(&owned[..], "eggplant");

1.22.0 · Source§

### impl<'a, 'b> From<Cow<'b, str>> for Box<dyn Error + 'a>

Source§

#### fn from(err: Cow<'b, str>) -> Box<dyn Error + 'a>

Converts a `Cow` into a box of dyn `Error`.

##### §Examples

    use std::error::Error;
    use std::borrow::Cow;

    let a_cow_str_error = Cow::from("a str error");
    let a_boxed_error = Box::<dyn Error>::from(a_cow_str_error);
    assert!(size_of::<Box<dyn Error>>() == size_of_val(&a_boxed_error))

1.22.0 · Source§

### impl<'a, 'b> From<Cow<'b, str>> for Box<dyn Error + Send + Sync + 'a>

Source§

#### fn from(err: Cow<'b, str>) -> Box<dyn Error + Send + Sync + 'a>

Converts a `Cow` into a box of dyn `Error` + `Send` + `Sync`.

##### §Examples

    use std::error::Error;
    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!(
        size_of::<Box<dyn Error + Send + Sync>>() == size_of_val(&a_boxed_error))

1.0.0 · Source§

### impl<'a> From<String> for Cow<'a, str>

Source§

#### fn from(s: String) -> Cow<'a, str>

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));

1.8.0 · Source§

### impl<'a, T: Clone> From<Vec<T>> for Cow<'a, [T]>

Source§

#### fn from(v: Vec<T>) -> Cow<'a, [T]>

Creates an `Owned` variant of `Cow` from an owned instance of `Vec`.

This conversion does not allocate or clone the data.

1.12.0 · Source§

### impl<'a, 'b> FromIterator<&'b str> for 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
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### impl<'a> FromIterator<AsciiChar> for Cow<'a, str>

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#### fn from_iter<T: IntoIterator<Item = Char>>(it: T) -> Self

Creates a value from an iterator. Read more
1.80.0 · Source§

### impl<'a> FromIterator<Cow<'a, str>> for Box<str>

Source§

#### fn from_iter<T: IntoIterator<Item = Cow<'a, str>>>(iter: T) -> Self

Creates a value from an iterator. Read more
1.19.0 · Source§

### impl<'a> FromIterator<Cow<'a, str>> for String

Source§

#### fn from_iter<I: IntoIterator<Item = Cow<'a, str>>>(iter: I) -> String

Creates a value from an iterator. Read more
1.12.0 · Source§

### impl<'a> FromIterator<String> for Cow<'a, str>

Source§

#### fn from_iter<I: IntoIterator<Item = String>>(it: I) -> Cow<'a, str>

Creates a value from an iterator. Read more
1.0.0 · Source§

### impl<'a, T> FromIterator<T> for Cow<'a, [T]>
where T: Clone,

Source§

#### fn from_iter<I: IntoIterator<Item = T>>(it: I) -> Cow<'a, [T]>

Creates a value from an iterator. Read more
1.12.0 · Source§

### impl<'a> FromIterator<char> for 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
1.0.0 · Source§

### impl<B> Hash for Cow<'_, B>
where B: Hash + ToOwned + ?Sized,

Source§

#### fn hash<H: Hasher>(&self, state: &mut H)

Feeds this value into the given `Hasher`. Read more
1.3.0 · Source§

#### fn hash_slice<H>(data: &[Self], state: &mut H)
where H: Hasher, Self: Sized,

Feeds a slice of this type into the given `Hasher`. Read more
1.0.0 · Source§

### impl<B> Ord for Cow<'_, B>
where B: Ord + ToOwned + ?Sized,

Source§

#### fn cmp(&self, other: &Self) -> Ordering

This method returns an `Ordering` between `self` and `other`. Read more
1.21.0 (const: unstable) · Source§

#### fn max(self, other: Self) -> Self
where Self: Sized,

Compares and returns the maximum of two values. Read more
1.21.0 (const: unstable) · Source§

#### fn min(self, other: Self) -> Self
where Self: Sized,

Compares and returns the minimum of two values. Read more
1.50.0 (const: unstable) · Source§

#### fn clamp(self, min: Self, max: Self) -> Self
where Self: Sized,

Restrict a value to a certain interval. Read more
1.0.0 · Source§

### impl<T, U> PartialEq<&[U]> for Cow<'_, [T]>
where T: PartialEq<U> + Clone,

Source§

#### fn eq(&self, other: &&[U]) -> bool

Tests for `self` and `other` values to be equal, and is used by `==`.
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#### fn ne(&self, other: &&[U]) -> bool

Tests for `!=`. The default implementation is almost always sufficient, and should not be overridden without very good reason.
Source§

### impl PartialEq<&ByteStr> for Cow<'_, [u8]>

Source§

#### fn eq(&self, other: &&ByteStr) -> bool

Tests for `self` and `other` values to be equal, and is used by `==`.
1.0.0 (const: unstable) · Source§

#### fn ne(&self, other: &Rhs) -> bool

Tests for `!=`. The default implementation is almost always sufficient, and should not be overridden without very good reason.
Source§

### impl PartialEq<&ByteStr> for Cow<'_, ByteStr>

Source§

#### fn eq(&self, other: &&ByteStr) -> bool

Tests for `self` and `other` values to be equal, and is used by `==`.
1.0.0 (const: unstable) · Source§

#### fn ne(&self, other: &Rhs) -> bool

Tests for `!=`. The default implementation is almost always sufficient, and should not be overridden without very good reason.
Source§

### impl PartialEq<&ByteStr> for Cow<'_, str>

Source§

#### fn eq(&self, other: &&ByteStr) -> bool

Tests for `self` and `other` values to be equal, and is used by `==`.
1.0.0 (const: unstable) · Source§

#### fn ne(&self, other: &Rhs) -> bool

Tests for `!=`. The default implementation is almost always sufficient, and should not be overridden without very good reason.
1.90.0 · Source§

### impl PartialEq<&CStr> for Cow<'_, CStr>

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#### fn eq(&self, other: &&CStr) -> bool

Tests for `self` and `other` values to be equal, and is used by `==`.
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#### fn ne(&self, other: &&CStr) -> bool

Tests for `!=`. The default implementation is almost always sufficient, and should not be overridden without very good reason.
1.0.0 · Source§

### impl<T, U> PartialEq<&mut [U]> for Cow<'_, [T]>
where T: PartialEq<U> + Clone,

Source§

#### fn eq(&self, other: &&mut [U]) -> bool

Tests for `self` and `other` values to be equal, and is used by `==`.
Source§

#### fn ne(&self, other: &&mut [U]) -> bool

Tests for `!=`. The default implementation is almost always sufficient, and should not be overridden without very good reason.
1.0.0 · Source§

### impl PartialEq<&str> for Cow<'_, str>

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#### fn eq(&self, other: &&str) -> bool

Tests for `self` and `other` values to be equal, and is used by `==`.
Source§

#### fn ne(&self, other: &&str) -> bool

Tests for `!=`. The default implementation is almost always sufficient, and should not be overridden without very good reason.
Source§

### impl PartialEq<ByteString> for Cow<'_, [u8]>

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#### fn eq(&self, other: &ByteString) -> bool

Tests for `self` and `other` values to be equal, and is used by `==`.
1.0.0 (const: unstable) · Source§

#### fn ne(&self, other: &Rhs) -> bool

Tests for `!=`. The default implementation is almost always sufficient, and should not be overridden without very good reason.
Source§

### impl PartialEq<ByteString> for Cow<'_, ByteStr>

Source§

#### fn eq(&self, other: &ByteString) -> bool

Tests for `self` and `other` values to be equal, and is used by `==`.
1.0.0 (const: unstable) · Source§

#### fn ne(&self, other: &Rhs) -> bool

Tests for `!=`. The default implementation is almost always sufficient, and should not be overridden without very good reason.
Source§

### impl PartialEq<ByteString> for Cow<'_, str>

Source§

#### fn eq(&self, other: &ByteString) -> bool

Tests for `self` and `other` values to be equal, and is used by `==`.
1.0.0 (const: unstable) · Source§

#### fn ne(&self, other: &Rhs) -> bool

Tests for `!=`. The default implementation is almost always sufficient, and should not be overridden without very good reason.
1.90.0 · Source§

### impl PartialEq<CStr> for Cow<'_, CStr>

Source§

#### fn eq(&self, other: &CStr) -> bool

Tests for `self` and `other` values to be equal, and is used by `==`.
Source§

#### fn ne(&self, other: &CStr) -> bool

Tests for `!=`. The default implementation is almost always sufficient, and should not be overridden without very good reason.
1.90.0 · Source§

### impl PartialEq<CString> for Cow<'_, CStr>

Source§

#### fn eq(&self, other: &CString) -> bool

Tests for `self` and `other` values to be equal, and is used by `==`.
Source§

#### fn ne(&self, other: &CString) -> bool

Tests for `!=`. The default implementation is almost always sufficient, and should not be overridden without very good reason.
Source§

### impl PartialEq<Cow<'_, [u8]>> for &ByteStr

Source§

#### fn eq(&self, other: &Cow<'_, [u8]>) -> bool

Tests for `self` and `other` values to be equal, and is used by `==`.
1.0.0 (const: unstable) · Source§

#### fn ne(&self, other: &Rhs) -> bool

Tests for `!=`. The default implementation is almost always sufficient, and should not be overridden without very good reason.
Source§

### impl PartialEq<Cow<'_, [u8]>> for ByteString

Source§

#### fn eq(&self, other: &Cow<'_, [u8]>) -> bool

Tests for `self` and `other` values to be equal, and is used by `==`.
1.0.0 (const: unstable) · Source§

#### fn ne(&self, other: &Rhs) -> bool

Tests for `!=`. The default implementation is almost always sufficient, and should not be overridden without very good reason.
Source§

### impl PartialEq<Cow<'_, ByteStr>> for &ByteStr

Source§

#### fn eq(&self, other: &Cow<'_, ByteStr>) -> bool

Tests for `self` and `other` values to be equal, and is used by `==`.
1.0.0 (const: unstable) · Source§

#### fn ne(&self, other: &Rhs) -> bool

Tests for `!=`. The default implementation is almost always sufficient, and should not be overridden without very good reason.
Source§

### impl PartialEq<Cow<'_, ByteStr>> for ByteString

Source§

#### fn eq(&self, other: &Cow<'_, ByteStr>) -> bool

Tests for `self` and `other` values to be equal, and is used by `==`.
1.0.0 (const: unstable) · Source§

#### fn ne(&self, other: &Rhs) -> bool

Tests for `!=`. The default implementation is almost always sufficient, and should not be overridden without very good reason.
1.90.0 · Source§

### impl PartialEq<Cow<'_, CStr>> for CStr

Source§

#### fn eq(&self, other: &Cow<'_, Self>) -> bool

Tests for `self` and `other` values to be equal, and is used by `==`.
Source§

#### fn ne(&self, other: &Cow<'_, Self>) -> bool

Tests for `!=`. The default implementation is almost always sufficient, and should not be overridden without very good reason.
1.90.0 · Source§

### impl PartialEq<Cow<'_, CStr>> for CString

Source§

#### fn eq(&self, other: &Cow<'_, CStr>) -> bool

Tests for `self` and `other` values to be equal, and is used by `==`.
Source§

#### fn ne(&self, other: &Cow<'_, CStr>) -> bool

Tests for `!=`. The default implementation is almost always sufficient, and should not be overridden without very good reason.
Source§

### impl PartialEq<Cow<'_, str>> for &ByteStr

Source§

#### fn eq(&self, other: &Cow<'_, str>) -> bool

Tests for `self` and `other` values to be equal, and is used by `==`.
1.0.0 (const: unstable) · Source§

#### fn ne(&self, other: &Rhs) -> bool

Tests for `!=`. The default implementation is almost always sufficient, and should not be overridden without very good reason.
1.0.0 · Source§

### impl PartialEq<Cow<'_, str>> for &str

Source§

#### fn eq(&self, other: &Cow<'_, str>) -> bool

Tests for `self` and `other` values to be equal, and is used by `==`.
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#### fn ne(&self, other: &Cow<'_, str>) -> bool

Tests for `!=`. The default implementation is almost always sufficient, and should not be overridden without very good reason.
Source§

### impl PartialEq<Cow<'_, str>> for ByteString

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#### fn eq(&self, other: &Cow<'_, str>) -> bool

Tests for `self` and `other` values to be equal, and is used by `==`.
1.0.0 (const: unstable) · Source§

#### fn ne(&self, other: &Rhs) -> bool

Tests for `!=`. The default implementation is almost always sufficient, and should not be overridden without very good reason.
1.0.0 · Source§

### impl PartialEq<Cow<'_, str>> for String

Source§

#### fn eq(&self, other: &Cow<'_, str>) -> bool

Tests for `self` and `other` values to be equal, and is used by `==`.
Source§

#### fn ne(&self, other: &Cow<'_, str>) -> bool

Tests for `!=`. The default implementation is almost always sufficient, and should not be overridden without very good reason.
1.0.0 · Source§

### impl PartialEq<Cow<'_, str>> for str

Source§

#### fn eq(&self, other: &Cow<'_, str>) -> bool

Tests for `self` and `other` values to be equal, and is used by `==`.
Source§

#### fn ne(&self, other: &Cow<'_, str>) -> bool

Tests for `!=`. The default implementation is almost always sufficient, and should not be overridden without very good reason.
1.0.0 · Source§

### impl<'a, 'b, B, C> PartialEq<Cow<'b, C>> for Cow<'a, B>
where B: PartialEq<C> + ToOwned + ?Sized, C: ToOwned + ?Sized,

Source§

#### fn eq(&self, other: &Cow<'b, C>) -> bool

Tests for `self` and `other` values to be equal, and is used by `==`.
1.0.0 (const: unstable) · Source§

#### fn ne(&self, other: &Rhs) -> bool

Tests for `!=`. The default implementation is almost always sufficient, and should not be overridden without very good reason.
1.0.0 · Source§

### impl PartialEq<String> for Cow<'_, str>

Source§

#### fn eq(&self, other: &String) -> bool

Tests for `self` and `other` values to be equal, and is used by `==`.
Source§

#### fn ne(&self, other: &String) -> bool

Tests for `!=`. The default implementation is almost always sufficient, and should not be overridden without very good reason.
1.0.0 · Source§

### impl<T, U, A: Allocator> PartialEq<Vec<U, A>> for Cow<'_, [T]>
where T: PartialEq<U> + Clone,

Source§

#### fn eq(&self, other: &Vec<U, A>) -> bool

Tests for `self` and `other` values to be equal, and is used by `==`.
Source§

#### fn ne(&self, other: &Vec<U, A>) -> bool

Tests for `!=`. The default implementation is almost always sufficient, and should not be overridden without very good reason.
1.0.0 · Source§

### impl PartialEq<str> for Cow<'_, str>

Source§

#### fn eq(&self, other: &str) -> bool

Tests for `self` and `other` values to be equal, and is used by `==`.
Source§

#### fn ne(&self, other: &str) -> bool

Tests for `!=`. The default implementation is almost always sufficient, and should not be overridden without very good reason.
Source§

### impl PartialOrd<&ByteStr> for Cow<'_, [u8]>

Source§

#### fn partial_cmp(&self, other: &&ByteStr) -> Option<Ordering>

This method returns an ordering between `self` and `other` values if one exists. Read more
1.0.0 (const: unstable) · Source§

#### fn lt(&self, other: &Rhs) -> bool

Tests less than (for `self` and `other`) and is used by the `<` operator. Read more
1.0.0 (const: unstable) · Source§

#### fn le(&self, other: &Rhs) -> bool

Tests less than or equal to (for `self` and `other`) and is used by the `<=` operator. Read more
1.0.0 (const: unstable) · Source§

#### fn gt(&self, other: &Rhs) -> bool

Tests greater than (for `self` and `other`) and is used by the `>` operator. Read more
1.0.0 (const: unstable) · Source§

#### fn ge(&self, other: &Rhs) -> bool

Tests greater than or equal to (for `self` and `other`) and is used by the `>=` operator. Read more
Source§

### impl PartialOrd<&ByteStr> for Cow<'_, ByteStr>

Source§

#### fn partial_cmp(&self, other: &&ByteStr) -> Option<Ordering>

This method returns an ordering between `self` and `other` values if one exists. Read more
1.0.0 (const: unstable) · Source§

#### fn lt(&self, other: &Rhs) -> bool

Tests less than (for `self` and `other`) and is used by the `<` operator. Read more
1.0.0 (const: unstable) · Source§

#### fn le(&self, other: &Rhs) -> bool

Tests less than or equal to (for `self` and `other`) and is used by the `<=` operator. Read more
1.0.0 (const: unstable) · Source§

#### fn gt(&self, other: &Rhs) -> bool

Tests greater than (for `self` and `other`) and is used by the `>` operator. Read more
1.0.0 (const: unstable) · Source§

#### fn ge(&self, other: &Rhs) -> bool

Tests greater than or equal to (for `self` and `other`) and is used by the `>=` operator. Read more
Source§

### impl PartialOrd<&ByteStr> for Cow<'_, str>

Source§

#### fn partial_cmp(&self, other: &&ByteStr) -> Option<Ordering>

This method returns an ordering between `self` and `other` values if one exists. Read more
1.0.0 (const: unstable) · Source§

#### fn lt(&self, other: &Rhs) -> bool

Tests less than (for `self` and `other`) and is used by the `<` operator. Read more
1.0.0 (const: unstable) · Source§

#### fn le(&self, other: &Rhs) -> bool

Tests less than or equal to (for `self` and `other`) and is used by the `<=` operator. Read more
1.0.0 (const: unstable) · Source§

#### fn gt(&self, other: &Rhs) -> bool

Tests greater than (for `self` and `other`) and is used by the `>` operator. Read more
1.0.0 (const: unstable) · Source§

#### fn ge(&self, other: &Rhs) -> bool

Tests greater than or equal to (for `self` and `other`) and is used by the `>=` operator. Read more
Source§

### impl PartialOrd<ByteString> for Cow<'_, [u8]>

Source§

#### fn partial_cmp(&self, other: &ByteString) -> Option<Ordering>

This method returns an ordering between `self` and `other` values if one exists. Read more
1.0.0 (const: unstable) · Source§

#### fn lt(&self, other: &Rhs) -> bool

Tests less than (for `self` and `other`) and is used by the `<` operator. Read more
1.0.0 (const: unstable) · Source§

#### fn le(&self, other: &Rhs) -> bool

Tests less than or equal to (for `self` and `other`) and is used by the `<=` operator. Read more
1.0.0 (const: unstable) · Source§

#### fn gt(&self, other: &Rhs) -> bool

Tests greater than (for `self` and `other`) and is used by the `>` operator. Read more
1.0.0 (const: unstable) · Source§

#### fn ge(&self, other: &Rhs) -> bool

Tests greater than or equal to (for `self` and `other`) and is used by the `>=` operator. Read more
Source§

### impl PartialOrd<ByteString> for Cow<'_, ByteStr>

Source§

#### fn partial_cmp(&self, other: &ByteString) -> Option<Ordering>

This method returns an ordering between `self` and `other` values if one exists. Read more
1.0.0 (const: unstable) · Source§

#### fn lt(&self, other: &Rhs) -> bool

Tests less than (for `self` and `other`) and is used by the `<` operator. Read more
1.0.0 (const: unstable) · Source§

#### fn le(&self, other: &Rhs) -> bool

Tests less than or equal to (for `self` and `other`) and is used by the `<=` operator. Read more
1.0.0 (const: unstable) · Source§

#### fn gt(&self, other: &Rhs) -> bool

Tests greater than (for `self` and `other`) and is used by the `>` operator. Read more
1.0.0 (const: unstable) · Source§

#### fn ge(&self, other: &Rhs) -> bool

Tests greater than or equal to (for `self` and `other`) and is used by the `>=` operator. Read more
Source§

### impl PartialOrd<ByteString> for Cow<'_, str>

Source§

#### fn partial_cmp(&self, other: &ByteString) -> Option<Ordering>

This method returns an ordering between `self` and `other` values if one exists. Read more
1.0.0 (const: unstable) · Source§

#### fn lt(&self, other: &Rhs) -> bool

Tests less than (for `self` and `other`) and is used by the `<` operator. Read more
1.0.0 (const: unstable) · Source§

#### fn le(&self, other: &Rhs) -> bool

Tests less than or equal to (for `self` and `other`) and is used by the `<=` operator. Read more
1.0.0 (const: unstable) · Source§

#### fn gt(&self, other: &Rhs) -> bool

Tests greater than (for `self` and `other`) and is used by the `>` operator. Read more
1.0.0 (const: unstable) · Source§

#### fn ge(&self, other: &Rhs) -> bool

Tests greater than or equal to (for `self` and `other`) and is used by the `>=` operator. Read more
Source§

### impl PartialOrd<Cow<'_, [u8]>> for &ByteStr

Source§

#### fn partial_cmp(&self, other: &Cow<'_, [u8]>) -> Option<Ordering>

This method returns an ordering between `self` and `other` values if one exists. Read more
1.0.0 (const: unstable) · Source§

#### fn lt(&self, other: &Rhs) -> bool

Tests less than (for `self` and `other`) and is used by the `<` operator. Read more
1.0.0 (const: unstable) · Source§

#### fn le(&self, other: &Rhs) -> bool

Tests less than or equal to (for `self` and `other`) and is used by the `<=` operator. Read more
1.0.0 (const: unstable) · Source§

#### fn gt(&self, other: &Rhs) -> bool

Tests greater than (for `self` and `other`) and is used by the `>` operator. Read more
1.0.0 (const: unstable) · Source§

#### fn ge(&self, other: &Rhs) -> bool

Tests greater than or equal to (for `self` and `other`) and is used by the `>=` operator. Read more
Source§

### impl PartialOrd<Cow<'_, [u8]>> for ByteString

Source§

#### fn partial_cmp(&self, other: &Cow<'_, [u8]>) -> Option<Ordering>

This method returns an ordering between `self` and `other` values if one exists. Read more
1.0.0 (const: unstable) · Source§

#### fn lt(&self, other: &Rhs) -> bool

Tests less than (for `self` and `other`) and is used by the `<` operator. Read more
1.0.0 (const: unstable) · Source§

#### fn le(&self, other: &Rhs) -> bool

Tests less than or equal to (for `self` and `other`) and is used by the `<=` operator. Read more
1.0.0 (const: unstable) · Source§

#### fn gt(&self, other: &Rhs) -> bool

Tests greater than (for `self` and `other`) and is used by the `>` operator. Read more
1.0.0 (const: unstable) · Source§

#### fn ge(&self, other: &Rhs) -> bool

Tests greater than or equal to (for `self` and `other`) and is used by the `>=` operator. Read more
Source§

### impl PartialOrd<Cow<'_, ByteStr>> for &ByteStr

Source§

#### fn partial_cmp(&self, other: &Cow<'_, ByteStr>) -> Option<Ordering>

This method returns an ordering between `self` and `other` values if one exists. Read more
1.0.0 (const: unstable) · Source§

#### fn lt(&self, other: &Rhs) -> bool

Tests less than (for `self` and `other`) and is used by the `<` operator. Read more
1.0.0 (const: unstable) · Source§

#### fn le(&self, other: &Rhs) -> bool

Tests less than or equal to (for `self` and `other`) and is used by the `<=` operator. Read more
1.0.0 (const: unstable) · Source§

#### fn gt(&self, other: &Rhs) -> bool

Tests greater than (for `self` and `other`) and is used by the `>` operator. Read more
1.0.0 (const: unstable) · Source§

#### fn ge(&self, other: &Rhs) -> bool

Tests greater than or equal to (for `self` and `other`) and is used by the `>=` operator. Read more
Source§

### impl PartialOrd<Cow<'_, ByteStr>> for ByteString

Source§

#### fn partial_cmp(&self, other: &Cow<'_, ByteStr>) -> Option<Ordering>

This method returns an ordering between `self` and `other` values if one exists. Read more
1.0.0 (const: unstable) · Source§

#### fn lt(&self, other: &Rhs) -> bool

Tests less than (for `self` and `other`) and is used by the `<` operator. Read more
1.0.0 (const: unstable) · Source§

#### fn le(&self, other: &Rhs) -> bool

Tests less than or equal to (for `self` and `other`) and is used by the `<=` operator. Read more
1.0.0 (const: unstable) · Source§

#### fn gt(&self, other: &Rhs) -> bool

Tests greater than (for `self` and `other`) and is used by the `>` operator. Read more
1.0.0 (const: unstable) · Source§

#### fn ge(&self, other: &Rhs) -> bool

Tests greater than or equal to (for `self` and `other`) and is used by the `>=` operator. Read more
Source§

### impl PartialOrd<Cow<'_, str>> for &ByteStr

Source§

#### fn partial_cmp(&self, other: &Cow<'_, str>) -> Option<Ordering>

This method returns an ordering between `self` and `other` values if one exists. Read more
1.0.0 (const: unstable) · Source§

#### fn lt(&self, other: &Rhs) -> bool

Tests less than (for `self` and `other`) and is used by the `<` operator. Read more
1.0.0 (const: unstable) · Source§

#### fn le(&self, other: &Rhs) -> bool

Tests less than or equal to (for `self` and `other`) and is used by the `<=` operator. Read more
1.0.0 (const: unstable) · Source§

#### fn gt(&self, other: &Rhs) -> bool

Tests greater than (for `self` and `other`) and is used by the `>` operator. Read more
1.0.0 (const: unstable) · Source§

#### fn ge(&self, other: &Rhs) -> bool

Tests greater than or equal to (for `self` and `other`) and is used by the `>=` operator. Read more
Source§

### impl PartialOrd<Cow<'_, str>> for ByteString

Source§

#### fn partial_cmp(&self, other: &Cow<'_, str>) -> Option<Ordering>

This method returns an ordering between `self` and `other` values if one exists. Read more
1.0.0 (const: unstable) · Source§

#### fn lt(&self, other: &Rhs) -> bool

Tests less than (for `self` and `other`) and is used by the `<` operator. Read more
1.0.0 (const: unstable) · Source§

#### fn le(&self, other: &Rhs) -> bool

Tests less than or equal to (for `self` and `other`) and is used by the `<=` operator. Read more
1.0.0 (const: unstable) · Source§

#### fn gt(&self, other: &Rhs) -> bool

Tests greater than (for `self` and `other`) and is used by the `>` operator. Read more
1.0.0 (const: unstable) · Source§

#### fn ge(&self, other: &Rhs) -> bool

Tests greater than or equal to (for `self` and `other`) and is used by the `>=` operator. Read more
1.0.0 · Source§

### impl<'a, B> PartialOrd for Cow<'a, B>
where B: PartialOrd + ToOwned + ?Sized,

Source§

#### 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
1.0.0 (const: unstable) · Source§

#### fn lt(&self, other: &Rhs) -> bool

Tests less than (for `self` and `other`) and is used by the `<` operator. Read more
1.0.0 (const: unstable) · Source§

#### fn le(&self, other: &Rhs) -> bool

Tests less than or equal to (for `self` and `other`) and is used by the `<=` operator. Read more
1.0.0 (const: unstable) · Source§

#### fn gt(&self, other: &Rhs) -> bool

Tests greater than (for `self` and `other`) and is used by the `>` operator. Read more
1.0.0 (const: unstable) · Source§

#### fn ge(&self, other: &Rhs) -> bool

Tests greater than or equal to (for `self` and `other`) and is used by the `>=` operator. Read more
Source§

### impl<T: Clone> DerefPure for Cow<'_, [T]>

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### impl<T: Clone> DerefPure for Cow<'_, T>

Source§

### impl DerefPure for Cow<'_, str>

1.0.0 · Source§

### impl<B> Eq for Cow<'_, B>
where B: Eq + ToOwned + ?Sized,

## Auto Trait Implementations§

§

### impl<'a, B> Freeze for Cow<'a, B>
where <B as ToOwned>::Owned: Freeze, B: ?Sized,

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### impl<'a, B> RefUnwindSafe for Cow<'a, B>
where <B as ToOwned>::Owned: RefUnwindSafe, B: RefUnwindSafe + ?Sized,

§

### impl<'a, B> Send for Cow<'a, B>
where <B as ToOwned>::Owned: Send, B: Sync + ?Sized,

§

### impl<'a, B> Sync for Cow<'a, B>
where <B as ToOwned>::Owned: Sync, B: Sync + ?Sized,

§

### impl<'a, B> Unpin for Cow<'a, B>
where <B as ToOwned>::Owned: Unpin, B: ?Sized,

§

### impl<'a, B> UnsafeUnpin for Cow<'a, B>
where <B as ToOwned>::Owned: UnsafeUnpin, B: ?Sized,

§

### impl<'a, B> UnwindSafe for Cow<'a, B>
where <B as ToOwned>::Owned: UnwindSafe, B: RefUnwindSafe + ?Sized,

## Blanket Implementations§

Source§

### impl<T> Any for T
where T: 'static + ?Sized,

Source§

#### fn type_id(&self) -> TypeId

Gets the `TypeId` of `self`. Read more
Source§

### impl<T> Borrow<T> for T
where T: ?Sized,

Source§

#### fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
Source§

### impl<T> BorrowMut<T> for T
where T: ?Sized,

Source§

#### fn borrow_mut(&mut self) -> &mut T

Mutably borrows from an owned value. Read more
Source§

### impl<T> CloneToUninit for T
where T: Clone,

Source§

#### unsafe fn clone_to_uninit(&self, dest: *mut u8)

🔬This is a nightly-only experimental API. (`clone_to_uninit` #126799)
Performs copy-assignment from `self` to `dest`. Read more
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### impl<T> From<T> for T

Source§

#### fn from(t: T) -> T

Returns the argument unchanged.

Source§

### impl<T, U> Into<U> for T
where U: From<T>,

Source§

#### fn into(self) -> U

Calls `U::from(self)`.

That is, this conversion is whatever the implementation of `From<T> for U` chooses to do.

Source§

### impl<P, T> Receiver for P
where P: Deref<Target = T> + ?Sized, T: ?Sized,

Source§

#### type Target = T

🔬This is a nightly-only experimental API. (`arbitrary_self_types` #44874)
The target type on which the method may be called.
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### impl<T> ToOwned for T
where T: Clone,

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#### type Owned = T

The resulting type after obtaining ownership.
Source§

#### fn to_owned(&self) -> T

Creates owned data from borrowed data, usually by cloning. Read more
Source§

#### fn clone_into(&self, target: &mut T)

Uses borrowed data to replace owned data, usually by cloning. Read more
Source§

### impl<T> ToString for T
where T: Display + ?Sized,

Source§

#### fn to_string(&self) -> String

Converts the given value to a `String`. Read more
Source§

### impl<T, U> TryFrom<U> for T
where U: Into<T>,

Source§

#### type Error = Infallible

The type returned in the event of a conversion error.
Source§

#### fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.
Source§

### impl<T, U> TryInto<U> for T
where U: TryFrom<T>,

Source§

#### type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.
Source§

#### fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.