cs431_homework::test::loom::prelude::rust_2024

Trait Clone

1.85.0 · 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.

Dyn Compatibility§

This trait is not dyn compatible.

In older versions of Rust, dyn compatibility was called "object safety", so this trait is not object safe.

Trait 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)

Dyn Compatibility§

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 crossbeam_channel::err::RecvTimeoutError

impl Clone for crossbeam_channel::err::TryRecvError

impl Clone for tpacket_versions

impl Clone for PrefilterConfig

impl Clone for BernoulliError

impl Clone for rand::distr::uniform::Error

impl Clone for rand::distr::weighted::Error

impl Clone for IndexVec

impl Clone for IndexVecIntoIter

impl Clone for regex::error::Error

impl Clone for StartError

impl Clone for WhichCaptures

impl Clone for State

impl Clone for regex_automata::util::look::Look

impl Clone for regex_automata::util::search::Anchored

impl Clone for regex_automata::util::search::MatchErrorKind

impl Clone for regex_automata::util::search::MatchKind

impl Clone for AssertionKind

impl Clone for Ast

impl Clone for ClassAsciiKind

impl Clone for ClassPerlKind

impl Clone for ClassSet

impl Clone for ClassSetBinaryOpKind

impl Clone for ClassSetItem

impl Clone for ClassUnicodeKind

impl Clone for ClassUnicodeOpKind

impl Clone for regex_syntax::ast::ErrorKind

impl Clone for Flag

impl Clone for FlagsItemKind

impl Clone for GroupKind

impl Clone for HexLiteralKind

impl Clone for LiteralKind

impl Clone for RepetitionKind

impl Clone for RepetitionRange

impl Clone for SpecialLiteralKind

impl Clone for regex_syntax::error::Error

impl Clone for Class

impl Clone for Dot

impl Clone for regex_syntax::hir::ErrorKind

impl Clone for HirKind

impl Clone for regex_syntax::hir::Look

impl Clone for ExtractKind

impl Clone for Utf8Sequence

impl Clone for zerocopy::byteorder::BigEndian

impl Clone for zerocopy::byteorder::LittleEndian

impl Clone for AsciiChar

impl Clone for cs431_homework::test::loom::cmp::Ordering

impl Clone for TryReserveErrorKind

impl Clone for Infallible

impl Clone for VarError

impl Clone for FromBytesWithNulError

impl Clone for cs431_homework::test::loom::fmt::Alignment

impl Clone for DebugAsHex

impl Clone for Sign

impl Clone for cs431_homework::test::loom::io::ErrorKind

impl Clone for SeekFrom

impl Clone for IpAddr

impl Clone for Ipv6MulticastScope

impl Clone for Shutdown

impl Clone for cs431_homework::test::loom::net::SocketAddr

impl Clone for FpCategory

impl Clone for IntErrorKind

Trait Clone

§How can I implement `Clone`?