flams_router_vscode::server_fn::inventory::core::clone

Trait Clone

pub trait Clone: Sized {
    // Required method
    fn clone(&self) -> Self;

    // Provided method
    fn clone_from(&mut self, source: &Self) { ... }
}

Expand description

A common trait that allows explicit creation of a duplicate value.

Calling clone always produces a new value. However, for types that are references to other data (such as smart pointers or references), the new value may still point to the same underlying data, rather than duplicating it. See Clone::clone for more details.

This distinction is especially important when using #[derive(Clone)] on structs containing smart pointers like Arc<Mutex<T>> - the cloned struct will share mutable state with the original.

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 duplicate of the value.

Note that what “duplicate” means varies by type:

For most types, this creates a deep, independent copy
For reference types like &T, this creates another reference to the same value
For smart pointers like Arc or Rc, this increments the reference count but still points to the same underlying data

§Examples

let hello = "Hello"; // &str implements Clone

assert_eq!("Hello", hello.clone());

Example with a reference-counted type:

use std::sync::{Arc, Mutex};

let data = Arc::new(Mutex::new(vec![1, 2, 3]));
let data_clone = data.clone(); // Creates another Arc pointing to the same Mutex

{
    let mut lock = data.lock().unwrap();
    lock.push(4);
}

// Changes are visible through the clone because they share the same underlying data
assert_eq!(*data_clone.lock().unwrap(), vec![1, 2, 3, 4]);

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 LoginError

impl Clone for ArchiveDatum

impl Clone for ArchiveIndex

impl Clone for DocumentKind

impl Clone for Institution

impl Clone for flams_ontology::content::declarations::symbols::AssocType

impl Clone for ArgMode

impl Clone for Informal

impl Clone for flams_ontology::content::terms::Term

impl Clone for flams_ontology::content::terms::Var

impl Clone for SlideElement

impl Clone for FTMLKey

impl Clone for flams_ontology::languages::Language

impl Clone for LOKind

impl Clone for NotationComponent

impl Clone for ParagraphFormatting

impl Clone for ParagraphKind

impl Clone for AnswerKind

impl Clone for CheckedResult

impl Clone for CognitiveDimension

impl Clone for FillInSolOption

impl Clone for FillinFeedbackKind

impl Clone for ProblemResponseType

impl Clone for QuizElement

impl Clone for SolutionData

impl Clone for SectionLevel

impl Clone for SearchIndex

impl Clone for SearchResult

impl Clone for SearchResultKind

impl Clone for ContentURI

impl Clone for URI

impl Clone for NarrativeURI

impl Clone for TermURI

impl Clone for LoginState

impl Clone for DocURIComponents

impl Clone for SymURIComponents

impl Clone for URIComponents

impl Clone for URIKind

impl Clone for FileState

impl Clone for AnyBackend

impl Clone for BackendChange

impl Clone for SandboxedRepository

impl Clone for Dependency

impl Clone for QueueMessage

impl Clone for TaskState

impl Clone for QueueName

impl Clone for CSS

impl Clone for CowStr

impl Clone for LogFileLine

impl Clone for LogLevel

impl Clone for LogTreeElem

impl Clone for flams_web_utils::components::drawer::DrawerSize

impl Clone for flams_web_utils::components::spinner::SpinnerSize

impl Clone for ThemeType

impl Clone for Env

impl Clone for flams_router_vscode::FromUtf8Error

impl Clone for ReloadWSProtocol

impl Clone for ServerFnErrorErr

impl Clone for LeptosConfigError

impl Clone for flams_router_vscode::server_fn::axum_export::extract::ws::Message

impl Clone for flams_router_vscode::server_fn::const_format::Case

impl Clone for AsciiChar

impl Clone for flams_router_vscode::server_fn::inventory::core::cmp::Ordering

impl Clone for flams_router_vscode::server_fn::inventory::core::convert::Infallible

impl Clone for FromBytesWithNulError

impl Clone for flams_router_vscode::server_fn::inventory::core::fmt::Alignment

impl Clone for DebugAsHex

impl Clone for flams_router_vscode::server_fn::inventory::core::fmt::Sign

impl Clone for flams_router_vscode::server_fn::inventory::core::net::IpAddr

Trait Clone

§How can I implement `Clone`?