uniffi::deps::static_assertions::_core::prelude::rust_2021

Trait Clone

1.55.0 · Source

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

    // Provided method
    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,
}

§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§

1.0.0 · 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§

1.0.0 · 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.

Dyn Compatibility§

This trait is not dyn compatible.

In older versions of Rust, dyn compatibility was called "object safety", so this trait is not object safe.

Trait CloneCopy item path

§Derivable

§How can I implement Clone?

§Additional implementors

Required Methods§

fn clone(&self) -> Self

§Examples

Provided Methods§

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

Dyn Compatibility§

Implementors§

impl Clone for AnsiColor

impl Clone for Color

impl Clone for Action

impl Clone for State

impl Clone for DependencyKind

impl Clone for Applicability

impl Clone for DiagnosticLevel

impl Clone for CargoOpt

impl Clone for Edition

impl Clone for Message

impl Clone for Cfg

impl Clone for CfgExpr

impl Clone for Platform

impl Clone for ArgAction

impl Clone for ArgPredicate

impl Clone for ValueHint

impl Clone for ContextKind

impl Clone for ContextValue

impl Clone for clap_builder::error::kind::ErrorKind

impl Clone for MatchesError

impl Clone for ValueSource

impl Clone for clap_builder::util::color::ColorChoice

impl Clone for colorchoice::ColorChoice

impl Clone for Container

impl Clone for StackFrameOffset

impl Clone for UnwindOperation

impl Clone for PrefilterConfig

impl Clone for nom::error::ErrorKind

impl Clone for VerboseErrorKind

impl Clone for Needed

impl Clone for Endianness

impl Clone for oneshot_uniffi::errors::RecvTimeoutError

impl Clone for oneshot_uniffi::errors::TryRecvError

impl Clone for plain::error::Error

impl Clone for StrCtx

impl Clone for Endian

impl Clone for Op

impl Clone for Category

impl Clone for serde_json::value::Value

impl Clone for Offset

impl Clone for toml::ser::Error

impl Clone for toml::value::Value

impl Clone for uniffi_bindgen::bindings::kotlin::gen_kotlin::ImportRequirement

impl Clone for uniffi_bindgen::bindings::python::gen_python::ImportRequirement

impl Clone for FfiType

impl Clone for UniffiTrait

impl Clone for ErrorMetadata

impl Clone for LiteralMetadata

impl Clone for uniffi_meta::Metadata

impl Clone for Radix

impl Clone for UniffiTraitMetadata

impl Clone for ExternalKind

impl Clone for ObjectImpl

impl Clone for uniffi_meta::types::Type

impl Clone for Special

impl Clone for StringifierOrInheritOrStatic

impl Clone for StringifierOrStatic

impl Clone for FloatingPointType

impl Clone for IntegerType

impl Clone for TargetLanguage

impl Clone for Level

impl Clone for LevelFilter

impl Clone for AsciiChar

impl Clone for uniffi::deps::static_assertions::_core::cmp::Ordering

impl Clone for Infallible

impl Clone for uniffi::deps::static_assertions::_core::fmt::Alignment

impl Clone for DebugAsHex

impl Clone for Sign

impl Clone for IpAddr

Trait Clone

§How can I implement `Clone`?