Crate dyn_clone

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This crate provides a DynClone trait that can be used in trait objects, and a clone_box function that can clone any sized or dynamically sized implementation of DynClone. Types that implement the standard library’s std::clone::Clone trait are automatically usable by a DynClone trait object.


use dyn_clone::DynClone;

trait MyTrait: DynClone {
    fn recite(&self);

impl MyTrait for String {
    fn recite(&self) {
        println!("{} ♫", self);

fn main() {
    let line = "The slithy structs did gyre and gimble the namespace";

    // Build a trait object holding a String.
    // This requires String to implement MyTrait and std::clone::Clone.
    let x: Box<dyn MyTrait> = Box::new(String::from(line));


    // The type of x2 is a Box<dyn MyTrait> cloned from x.
    let x2 = dyn_clone::clone_box(&*x);


This crate includes a macro for concisely implementing impl std::clone::Clone for Box<dyn MyTrait> in terms of dyn_clone::clone_box.

// As before.
trait MyTrait: DynClone {
    /* ... */


// Now data structures containing Box<dyn MyTrait> can derive Clone:
struct Container {
    trait_object: Box<dyn MyTrait>,

The clone_trait_object! macro expands to just the following, which you can handwrite instead if you prefer:

impl Clone for Box<dyn MyTrait> {
    fn clone(&self) -> Self {

// and similar for Box<dyn MyTrait + Send>, Box<dyn MyTrait + Sync>, Box<dyn MyTrait + Send + Sync>


  • Implement the standard library Clone for a trait object that has DynClone as a supertrait.