Trait frame_support::dispatch::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

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.

Object Safety§

This trait is not object safe.

Trait frame_support::dispatch::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)

Object Safety§

Implementors§

impl Clone for AhoCorasickKind

impl Clone for aho_corasick::packed::api::MatchKind

impl Clone for aho_corasick::util::error::MatchErrorKind

impl Clone for Candidate

impl Clone for aho_corasick::util::search::Anchored

impl Clone for aho_corasick::util::search::MatchKind

impl Clone for StartKind

impl Clone for arbitrary::error::Error

impl Clone for PrintFmt

impl Clone for DecodeError

impl Clone for DecodeSliceError

impl Clone for EncodeSliceError

impl Clone for DecodePaddingMode

impl Clone for Language

impl Clone for MnemonicType

impl Clone for bs58::alphabet::Error

impl Clone for bs58::decode::Error

impl Clone for bs58::encode::Error

impl Clone for byte_slice_cast::Error

impl Clone for byteorder::BigEndian

impl Clone for byteorder::LittleEndian

impl Clone for const_oid::error::Error

impl Clone for cpp_demangle::ast::ArrayType

impl Clone for BaseUnresolvedName

impl Clone for BuiltinType

impl Clone for CallOffset

impl Clone for ClassEnumType

impl Clone for CtorDtorName

impl Clone for Decltype

impl Clone for DestructorName

impl Clone for cpp_demangle::ast::Encoding

impl Clone for ExprPrimary

impl Clone for cpp_demangle::ast::Expression

impl Clone for GlobalCtorDtor

impl Clone for LocalName

impl Clone for MangledName

impl Clone for cpp_demangle::ast::Name

impl Clone for NestedName

impl Clone for OperatorName

impl Clone for cpp_demangle::ast::Prefix

impl Clone for PrefixHandle

impl Clone for RefQualifier

impl Clone for SimpleOperatorName

impl Clone for SpecialName

impl Clone for StandardBuiltinType

impl Clone for Substitution

impl Clone for TemplateArg

impl Clone for TemplateTemplateParamHandle

impl Clone for cpp_demangle::ast::Type

impl Clone for TypeHandle

impl Clone for UnqualifiedName

impl Clone for UnresolvedName

impl Clone for UnresolvedType

impl Clone for UnresolvedTypeHandle

impl Clone for UnscopedName

impl Clone for UnscopedTemplateNameHandle

impl Clone for VectorType

impl Clone for WellKnownComponent

impl Clone for DemangleNodeType

impl Clone for cpp_demangle::error::Error

impl Clone for Reloc

impl Clone for CursorPosition

impl Clone for DataValue

impl Clone for AtomicRmwOp

impl Clone for FloatCC

impl Clone for IntCC

impl Clone for ValueDef

impl Clone for AnyEntity

impl Clone for ValueLabelAssignments

Trait frame_support::dispatch::Clone

§How can I implement `Clone`?