core::traits::Copy

A trait for copying values. By default, variables in Cairo have ‘move semantics’, meaning they are moved when used. However, types implementing Copy have ‘copy semantics’, allowing the value to be duplicated instead of moved.

Signature

pub trait Copy

Examples

Without Copy (move semantics):

#[derive(Drop)]
struct Point {
    x: u128,
    y: u128,
}

fn main() {
    let p1 = Point { x: 5, y: 10 };
    foo(p1);
    foo(p1); // error: Variable was previously moved.
}

fn foo(p: Point) {}

With Copy (copy semantics):

#[derive(Copy, Drop)]
struct Point {
    x: u128,
    y: u128,
}

fn main() {
    let p1 = Point { x: 5, y: 10 };
    foo(p1);
    foo(p1); // works: `p1` is copied when passed to `foo`
}

fn foo(p: Point) {}