Rust by Example

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 Unit;

// A tuple struct with resources that implements the `Clone` trait

#[derive(Clone, Debug)]

struct Pair(Box, Box);

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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