Trait std::clone::Clone

1.0.0 · source · 
pub trait Clone: Sized {
    fn clone(&self) -> Self;

    fn clone_from(&mut self, source: &Self) { ... }
}
Expand description

A common trait for the ability to explicitly duplicate an object.

Differs from Copy in that Copy is implicit and an inexpensive bit-wise copy, while Clone is always explicit and may or may not be expensive. In order to enforce these characteristics, Rust does not allow you to reimplement Copy, but you may reimplement Clone and run arbitrary code.

Since Clone is more general than Copy, you can automatically make anything Copy be Clone as well.

Derivable

This trait can be used with #[derive] if all fields are Clone. The derived implementation of Clone calls clone on each field.

For a generic struct, #[derive] implements Clone conditionally by adding bound Clone on generic parameters.

// `derive` implements Clone for Reading<T> when T is Clone.
#[derive(Clone)]
struct Reading<T> {
    frequency: T,
}
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How can I implement Clone?

Types that are Copy should have a trivial implementation of Clone. More formally: if T: Copy, x: T, and y: &T, then let x = y.clone(); is equivalent to let x = *y;. Manual implementations should be careful to uphold this invariant; however, unsafe code must not rely on it to ensure memory safety.

An example is a generic struct holding a function pointer. In this case, the implementation of Clone cannot be derived, but can be implemented as:

struct Generate<T>(fn() -> T);

impl<T> Copy for Generate<T> {}

impl<T> Clone for Generate<T> {
    fn clone(&self) -> Self {
        *self
    }
}
Run

Additional implementors

In addition to the implementors listed below, the following types also implement Clone:

  • Function item types (i.e., the distinct types defined for each function)
  • Function pointer types (e.g., fn() -> i32)
  • Closure types, if they capture no value from the environment or if all such captured values implement Clone themselves. Note that variables captured by shared reference always implement Clone (even if the referent doesn’t), while variables captured by mutable reference never implement Clone.

Required Methods§

Returns a copy of the value.

Examples
let hello = "Hello"; // &str implements Clone

assert_eq!("Hello", hello.clone());
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Provided Methods§

Performs copy-assignment from source.

a.clone_from(&b) is equivalent to a = b.clone() in functionality, but can be overridden to reuse the resources of a to avoid unnecessary allocations.

Implementors§

1.27.0 · source§

impl Clone for __m128

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impl Clone for __m128bh

1.27.0 · source§

impl Clone for __m128d

1.27.0 · source§

impl Clone for __m128i

1.27.0 · source§

impl Clone for __m256

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impl Clone for __m256bh

1.27.0 · source§

impl Clone for __m256d

1.27.0 · source§

impl Clone for __m256i

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impl Clone for __m512

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impl Clone for __m512bh

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impl Clone for __m512d

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impl Clone for __m512i

This trait is implemented on function pointers with any number of arguments.

Shared references can be cloned, but mutable references cannot!

Shared references can be cloned, but mutable references cannot!

This trait is implemented on arbitrary-length tuples.