Trait radix_engine::types::radix_engine_common::prelude::rust::prelude::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 radix_engine::types::radix_engine_common::prelude::rust::prelude::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 DatabaseUpdate

impl Clone for PartitionDatabaseUpdates

impl Clone for AccessControllerCollection

impl Clone for AccessControllerFeature

impl Clone for AccessControllerField

impl Clone for AccessControllerTypedSubstateKey

impl Clone for AccessControllerError

impl Clone for PrimaryRoleBadgeWithdrawAttemptState

impl Clone for PrimaryRoleLockingState

impl Clone for PrimaryRoleRecoveryAttemptState

impl Clone for RecoveryRoleBadgeWithdrawAttemptState

impl Clone for RecoveryRoleRecoveryAttemptState

impl Clone for RecoveryRoleRecoveryState

impl Clone for AccountCollection

impl Clone for AccountFeature

impl Clone for AccountField

impl Clone for AccountTypedSubstateKey

impl Clone for AccountError

impl Clone for ConsensusManagerCollection

impl Clone for ConsensusManagerFeature

impl Clone for ConsensusManagerField

impl Clone for ConsensusManagerTypedSubstateKey

impl Clone for ConsensusManagerError

impl Clone for UpdateSecondaryIndex

impl Clone for ValidatorError

impl Clone for ValidatorCollection

impl Clone for ValidatorFeature

impl Clone for ValidatorField

impl Clone for ValidatorTypedSubstateKey

impl Clone for PackageError

impl Clone for PackageCollection

impl Clone for PackageFeature

impl Clone for PackageField

impl Clone for PackageTypedSubstateKey

impl Clone for radix_engine::blueprints::pool::v1::errors::multi_resource_pool::Error

impl Clone for radix_engine::blueprints::pool::v1::errors::one_resource_pool::Error

impl Clone for radix_engine::blueprints::pool::v1::errors::two_resource_pool::Error

impl Clone for PoolV1MinorVersion

impl Clone for MultiResourcePoolCollection

impl Clone for MultiResourcePoolFeature

impl Clone for MultiResourcePoolField

impl Clone for MultiResourcePoolTypedSubstateKey

impl Clone for OneResourcePoolCollection

impl Clone for OneResourcePoolFeature

impl Clone for OneResourcePoolField

impl Clone for OneResourcePoolTypedSubstateKey

impl Clone for TwoResourcePoolCollection

impl Clone for TwoResourcePoolFeature

impl Clone for TwoResourcePoolField

impl Clone for TwoResourcePoolTypedSubstateKey

impl Clone for ComposeProofError

impl Clone for AuthZoneError

impl Clone for BucketError

impl Clone for FungibleResourceManagerError

impl Clone for FungibleResourceManagerCollection

impl Clone for FungibleResourceManagerFeature

impl Clone for FungibleResourceManagerField

impl Clone for FungibleResourceManagerTypedSubstateKey

impl Clone for FungibleVaultCollection

impl Clone for FungibleVaultFeature

impl Clone for FungibleVaultField

impl Clone for FungibleVaultTypedSubstateKey

impl Clone for InvalidNonFungibleSchema

impl Clone for NonFungibleResourceManagerError

impl Clone for NonFungibleResourceManagerCollection

impl Clone for NonFungibleResourceManagerFeature

impl Clone for NonFungibleResourceManagerField

impl Clone for NonFungibleResourceManagerGeneric

impl Clone for NonFungibleResourceManagerTypedSubstateKey

§How can I implement `Clone`?