Clone - Rust By Example
Description: A description

# Clone

When dealing with resources, the default behavior is to transfer them during assignments or function calls. However, sometimes we need to make a copy of the resource as well.

The `Clone` trait helps us do exactly this. Most commonly, we can use the `.clone()` method defined by the `Clone` trait.

    // A unit struct without resources
    #[derive(Debug, Clone, Copy)]
    struct Nil;

    // A tuple struct with resources that implements the `Clone` trait
    #[derive(Clone, Debug)]
    struct Pair(Box<i32>, Box<i32>);

    fn main() {
        // Instantiate `Nil`
        let nil = Nil;
        // Copy `Nil`, there are no resources to move
        let copied_nil = nil;

        // Both `Nil`s can be used independently
        println!("original: {:?}", nil);
        println!("copy: {:?}", copied_nil);

        // Instantiate `Pair`
        let pair = Pair(Box::new(1), Box::new(2));
        println!("original: {:?}", pair);

        // Copy `pair` into `moved_pair`, moves resources
        let moved_pair = pair;
        println!("copy: {:?}", moved_pair);

        // Error! `pair` has lost its resources
        //println!("original: {:?}", pair);
        // TODO ^ Try uncommenting this line

        // Clone `moved_pair` into `cloned_pair` (resources are included)
        let cloned_pair = moved_pair.clone();
        // Drop the original pair using std::mem::drop
        drop(moved_pair);

        // Error! `moved_pair` has been dropped
        //println!("copy: {:?}", moved_pair);
        // TODO ^ Try uncommenting this line

        // The result from .clone() can still be used!
        println!("clone: {:?}", cloned_pair);
    }