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 it 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);
}