Trait devela::code::Clone

1.0.0 · source ·

pub trait Clone: Sized {
    // Required method
    fn clone(&self) -> Self;

    // Provided method
    fn clone_from(&mut self, source: &Self) { ... }
}

Expand description

core 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,
}

§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
    }
}

If we derive:

#[derive(Copy, Clone)]
struct Generate<T>(fn() -> T);

the auto-derived implementations will have unnecessary T: Copy and T: Clone bounds:


// Automatically derived
impl<T: Copy> Copy for Generate<T> { }

// Automatically derived
impl<T: Clone> Clone for Generate<T> {
    fn clone(&self) -> Generate<T> {
        Generate(Clone::clone(&self.0))
    }
}

The bounds are unnecessary because clearly the function itself should be copy- and cloneable even if its return type is not:

#[derive(Copy, Clone)]
struct Generate<T>(fn() -> T);

struct NotCloneable;

fn generate_not_cloneable() -> NotCloneable {
    NotCloneable
}

Generate(generate_not_cloneable).clone(); // error: trait bounds were not satisfied
// Note: With the manual implementations the above line will compile.

§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§

source

fn clone(&self) -> Self

Returns a copy of the value.

§Examples

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

assert_eq!("Hello", hello.clone());

Provided Methods§

source

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

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.

Object Safety§

This trait is not object safe.

Trait devela::code::Clone

§Derivable

§How can I implement Clone?

§Additional implementors

Required Methods§

fn clone(&self) -> Self

§Examples

Provided Methods§

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

Object Safety§

Implementors§

impl Clone for devela::_deps::bytemuck::__core::ascii::Char

impl Clone for devela::_deps::bytemuck::__core::fmt::Alignment

impl Clone for IpAddr

impl Clone for Ipv6MulticastScope

impl Clone for devela::_deps::bytemuck::__core::net::SocketAddr

impl Clone for FpCategory

impl Clone for IntErrorKind

impl Clone for SearchStep

impl Clone for CheckedCastError

impl Clone for PodCastError

impl Clone for SetCursorStyle

impl Clone for Attribute

impl Clone for Color

impl Clone for Colored

impl Clone for ClearType

impl Clone for devela::_deps::hashbrown::TryReserveError

impl Clone for PrefilterConfig

impl Clone for AppleGfxApi

impl Clone for Backend

impl Clone for BlendFactor

impl Clone for BlendValue

impl Clone for BufferType

impl Clone for BufferUsage

impl Clone for CompareFunc

impl Clone for Comparison

impl Clone for CullFace

impl Clone for CursorIcon

impl Clone for Equation

impl Clone for FilterMode

impl Clone for FrontFaceOrder

impl Clone for KeyCode

impl Clone for MipmapFilterMode

impl Clone for MouseButton

impl Clone for PrimitiveType

impl Clone for RawId

impl Clone for ShaderError

impl Clone for ShaderType

impl Clone for StencilOp

impl Clone for TextureAccess

impl Clone for TextureFormat

impl Clone for TextureKind

impl Clone for TextureWrap

impl Clone for TouchPhase

impl Clone for UniformType

impl Clone for VertexFormat

impl Clone for VertexStep

impl Clone for TryReserveErrorKind

impl Clone for VarError

impl Clone for SeekFrom

impl Clone for Shutdown

impl Clone for BacktraceStyle

impl Clone for RecvTimeoutError

impl Clone for TryRecvError

impl Clone for devela::all::AtomicOrdering

impl Clone for ErrorKind

impl Clone for Infallible

impl Clone for devela::all::Ordering

impl Clone for DataError

impl Clone for ColorErrors

impl Clone for GfxError

impl Clone for NumError

impl Clone for Sign

impl Clone for NeverOk

impl Clone for devela::text::AsciiChar

impl Clone for Month

impl Clone for TimeError

impl Clone for Weekday

impl Clone for AnsiColor3b

impl Clone for _Unwind_Action

§How can I implement `Clone`?