Trait radix_engine_common::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_common::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 Bech32Case

impl Clone for AddressBech32DecodeError

impl Clone for AddressBech32EncodeError

impl Clone for ParseBlsPublicKeyError

impl Clone for ParseBlsSignatureError

impl Clone for ParseEd25519PublicKeyError

impl Clone for ParseEd25519SignatureError

impl Clone for ParseHashError

impl Clone for radix_engine_common::crypto::public_key::PublicKey

impl Clone for PublicKeyHash

impl Clone for ParseSecp256k1PublicKeyError

impl Clone for ParseSecp256k1SignatureError

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 ParseManifestAddressReservationError

impl Clone for ParseManifestBlobRefError

impl Clone for ParseManifestBucketError

impl Clone for ParseManifestDecimalError

impl Clone for ManifestExpression

impl Clone for ParseManifestExpressionError

impl Clone for ManifestNonFungibleLocalId

impl Clone for ManifestNonFungibleLocalIdValidationError

impl Clone for ParseManifestPreciseDecimalError

impl Clone for ParseManifestProofError

impl Clone for OwnValidation

impl Clone for ReferenceValidation

impl Clone for ScryptoCustomTypeKind

impl Clone for ScryptoCustomTypeValidation

impl Clone for ScryptoCustomTraversal

impl Clone for ScryptoCustomValue

impl Clone for ScryptoCustomValueKind

impl Clone for NonFungibleIdType

impl Clone for ContentValidationError

impl Clone for NonFungibleLocalId

impl Clone for ParseNonFungibleLocalIdError

impl Clone for ParseOwnError

impl Clone for ParseReferenceError

impl Clone for DisplayMode

impl Clone for FormattingError

impl Clone for PrintMode

impl Clone for SerializationMode

impl Clone for ValueContext

impl Clone for ParseI192Error

impl Clone for ParseI256Error

impl Clone for ParseI320Error

impl Clone for ParseI384Error

impl Clone for ParseI448Error

impl Clone for ParseI512Error

impl Clone for ParseI768Error

impl Clone for ParseU192Error

impl Clone for ParseU256Error

impl Clone for ParseU320Error

impl Clone for ParseU384Error

impl Clone for ParseU448Error

impl Clone for ParseU512Error

impl Clone for ParseU768Error

impl Clone for ParseDecimalError

impl Clone for ParsePreciseDecimalError

impl Clone for RoundingMode

impl Clone for TimeComparisonOperator

impl Clone for DateTimeError

impl Clone for ParseUtcDateTimeError

impl Clone for ParseComponentAddressError

impl Clone for ParseGlobalAddressError

§How can I implement `Clone`?