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.

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// A unit struct without resources
#[derive(Debug, Clone, Copy)]
struct Unit;
// A tuple struct with resources that implements the `Clone` trait
#[derive(Clone, Debug)]
struct Pair(Box<i32>, Box<i32>);
fn main() {
    // Instantiate `Unit`
    let unit = Unit;
    // Copy `Unit`, there are no resources to move
    let copied_unit = unit;
    // Both `Unit`s can be used independently
    println!("original: {:?}", unit);
    println!("copy: {:?}", copied_unit);
    // Instantiate `Pair`
    let pair = Pair(Box::new(1), Box::new(2));
    println!("original: {:?}", pair);
    // Move `pair` into `moved_pair`, moves resources
    let moved_pair = pair;
    println!("moved: {:?}", 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);
}
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