Trait gclient::ext::sp_core::sp_std::clone::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§

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 gclient::ext::sp_core::sp_std::clone::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 CostToken

impl Clone for ChargeError

impl Clone for ChargeResult

impl Clone for CounterType

impl Clone for LockId

impl Clone for gear_core::memory::AllocError

impl Clone for gear_core::memory::MemoryError

impl Clone for MemorySetupError

impl Clone for MessageDetails

impl Clone for DispatchKind

impl Clone for MessageWaitedType

impl Clone for GasReservationState

impl Clone for ExecutionError

impl Clone for ExtError

impl Clone for gear_core_errors::MemoryError

impl Clone for MessageError

impl Clone for ReservationError

impl Clone for ErrorReplyReason

impl Clone for gear_core_errors::simple::ReplyCode

impl Clone for SignalCode

impl Clone for SimpleExecutionError

impl Clone for SimpleProgramCreationError

impl Clone for SuccessReplyReason

impl Clone for BacktraceStatus

impl Clone for DispatchStatus

impl Clone for gclient::Event

impl Clone for gclient::metadata::runtime_types::gear_common::event::Reason<UserMessageReadRuntimeReason, UserMessageReadSystemReason>

impl Clone for gclient::metadata::runtime_types::gear_core_errors::simple::ReplyCode

impl Clone for DeriveError

impl Clone for DeriveJunction

impl Clone for SecretStringError

impl Clone for ArithmeticError

impl Clone for gclient::ext::sp_runtime::DigestItem

impl Clone for gclient::ext::sp_runtime::DispatchError

impl Clone for gclient::ext::sp_runtime::MultiSignature

impl Clone for MultiSigner

impl Clone for Rounding

impl Clone for RuntimeString

impl Clone for StateVersion

impl Clone for TokenError

impl Clone for TransactionalError

impl Clone for gclient::ext::sp_runtime::generic::Era

impl Clone for gclient::ext::sp_runtime::legacy::byte_sized_error::DispatchError

impl Clone for HttpError

impl Clone for HttpRequestStatus

impl Clone for OffchainOverlayedChange

impl Clone for StorageKind

impl Clone for gclient::ext::sp_runtime::offchain::http::Error

impl Clone for gclient::ext::sp_runtime::offchain::http::Method

impl Clone for TypeDefPrimitive

impl Clone for MetaForm

impl Clone for PortableForm

impl Clone for InvalidTransaction

impl Clone for TransactionSource

impl Clone for TransactionValidityError

impl Clone for UnknownTransaction

impl Clone for TryReserveErrorKind

impl Clone for SearchStep

impl Clone for PublicError

impl Clone for Ss58AddressFormatRegistry

impl Clone for LogLevel

impl Clone for LogLevelFilter

impl Clone for Void

impl Clone for ChildInfo

impl Clone for ChildType

impl Clone for CallContext

impl Clone for gclient::ext::sp_core::sp_std::cmp::Ordering

impl Clone for Infallible

impl Clone for FpCategory

§How can I implement `Clone`?