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));

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));

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)
);

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

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

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

Converts the string reference into a Cow::Borrowed.

Converts the string reference into a Cow::Borrowed.

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.

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

This conversion does not allocate or clone the data.

Creates a Borrowed variant of Cow from a slice.

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

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

Creates a boxed Path from a clone-on-write pointer.

Converting from a Cow::Owned does not clone or allocate.

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.

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}");

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[..]);

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[..]);

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

Converts a Cow<'a, OsStr> into an OsString, by copying the contents if they are borrowed.

Converts a clone-on-write pointer to an owned path.

Converting from a Cow::Owned does not clone or allocate.

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 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");

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))

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))

Moves the string into a Cow::Owned.

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.