Trait scrypto::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 scrypto::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 AddressBech32DecodeError

impl Clone for AddressBech32EncodeError

impl Clone for AttachedModuleId

impl Clone for KeyValueStoreDataSchema

impl Clone for ModuleId

impl Clone for FallToOwner

impl Clone for MetadataConversionError

impl Clone for Proposer

impl Clone for Role

impl Clone for DefaultDepositRule

impl Clone for ResourcePreference

impl Clone for TimePrecisionV1

impl Clone for TimePrecisionV2

impl Clone for BlueprintPartitionType

impl Clone for BlueprintPayloadDef

impl Clone for BlueprintPayloadIdentifier

impl Clone for BlueprintType

impl Clone for FunctionAuth

impl Clone for InputOrOutput

impl Clone for KeyOrValue

impl Clone for MethodAuthTemplate

impl Clone for PartitionDescription

impl Clone for RoleSpecification

impl Clone for SystemInstruction

impl Clone for VmType

impl Clone for AccessRule

impl Clone for AccessRuleNode

impl Clone for GlobalCaller

impl Clone for MethodAccessibility

impl Clone for NonFungibleDataSchema

impl Clone for OwnerRole

impl Clone for OwnerRoleUpdater

impl Clone for ParseNonFungibleGlobalIdError

impl Clone for ProofRule

impl Clone for ResourceError

impl Clone for ResourceFeature

impl Clone for ResourceOrNonFungible

impl Clone for ResourceType

impl Clone for WithdrawStrategy

impl Clone for InstructionOutput

impl Clone for ComponentCastError

impl Clone for ObjectStubHandle

impl Clone for ParseBlsPublicKeyError

impl Clone for ParseBlsSignatureError

impl Clone for ParseEd25519PublicKeyError

impl Clone for ParseEd25519SignatureError

impl Clone for ParseHashError

impl Clone for ParseSecp256k1PublicKeyError

impl Clone for ParseSecp256k1SignatureError

impl Clone for scrypto::crypto::PublicKey

impl Clone for PublicKeyHash

impl Clone for ManifestCustomExtension

impl Clone for ManifestCustomTraversal

impl Clone for ManifestCustomValue

impl Clone for ManifestCustomValueKind

impl Clone for ManifestToRustValueError

impl Clone for RustToManifestValueError

impl Clone for ManifestAddress

impl Clone for ManifestExpression

impl Clone for ManifestNonFungibleLocalId

impl Clone for ManifestNonFungibleLocalIdValidationError

impl Clone for ParseManifestAddressReservationError

impl Clone for ParseManifestBlobRefError

impl Clone for ParseManifestBucketError

impl Clone for ParseManifestDecimalError

impl Clone for ParseManifestExpressionError

impl Clone for ParseManifestPreciseDecimalError

impl Clone for ParseManifestProofError

impl Clone for OwnValidation

§How can I implement `Clone`?