clone-on-capture

This crate provides a macro that makes all captures clone automatically.

Use case

Given this code snippet:

fn foo() {
    let a = "a".to_string();
    let _closure = move || {
        println!("{}, a");
    };
    println!("{}, a");
}

You will get an error that a was moved. To fix it you can clone a in a temporary scope:

fn foo() {
    let a = "a".to_string();
    let _closure = {
        let a = a.clone();
        move || {
            println!("{}, a");
        }
    };
    println!("{}, a");
}

Cloning can get tedious, clone-on-capture macro can automatically generate that code for you:

#[clone_on_capture]
fn foo() {
    let a = "a".to_string();
    let _closure = move || {
        println!("{}, a");
    };
    println!("{}, a");
}

This will also clone variables that implement Copy, but it is not a problem as .clone() is just an explicit way to do the same as Copy. https://doc.rust-lang.org/std/marker/trait.Copy.html#whats-the-difference-between-copy-and-clone

Do not clone prefix

Use dc_ prefix to prevent variable from being cloned.

#[clone_on_capture]
fn do_not_clone_prefix() {
    let dc_a = "a".to_string();
    let dc_a_address = dc_a.as_ptr();

    let closure = move || {
        let b = dc_a;
        let b_address = b.as_ptr();
        assert_eq!(dc_a_address, b_address);
    };

    closure();
}

Known caveats

Capturing arguments in string-formatting macros doesn't work:

#[clone_on_capture]
fn foo() {
    let a = "a".to_string();
    let _closure = move || {
        println!("{a}");
    };
    println!("{a}");
}