Rust-specific Patterns

Recipe	Crates	Categories
Clone a Struct Storing a Boxed Trait Object
pin-project and pin-project-lite

Clone a Struct Storing a Boxed Trait Object

The dyn-clone⮳ 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.

//! Demonstrates how to clone trait objects using the `dyn_clone` crate.

use dyn_clone::DynClone;

// Define a trait named `MyTrait` that requires implementors to also implement
// `DynClone`.
trait MyTrait: DynClone {
    fn recite(&self);
}

// Implement `MyTrait` for `String``.
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`.
    let original_trait_object: Box<dyn MyTrait> = Box::new(String::from(line));

    // Call the `MyTrait` function.
    original_trait_object.recite();

    // Clone the trait object.
    let cloned_trait_object: Box<dyn MyTrait> =
        dyn_clone::clone_box(&*original_trait_object);

    // Call the `MyTrait` function on the cloned object.
    cloned_trait_object.recite();
}

pin-project and pin-project-lite

pin-project⮳ is a crate for safe and ergonomic pin-projection. The #[pin_project] attribute creates projection types covering all the fields of struct or enum.

pin-project-lite is a lightweight version of pin-project written with declarative macros. The pin_project! macro creates a projection type covering all the fields of struct.

// // COMING SOON

See also:

• Projections and Structural Pinning⮳.
• std::pin::Pin⮳.