The Copy trait marks Rust types whose values can be duplicated implicitly, allowing the original binding to remain usable instead of transferring ownership. It matters when a value must be passed to a function more than once. section 2.1
Admiring the same artwork twice
An artwork containing a String is passed to admire_art twice. The first call moves art1 into the function, so the second call fails with “use of moved value”; the diagnostic notes that Artwork does not implement Copy. section 2.1
Listing 2.5 A program attempting to admire the same art twice
struct Artwork {
name: String,
}
fn admire_art(art: Artwork) {
println!("Wow, {} really makes you think.", art.name);
}
fn main() {
let art1 = Artwork { name: "The Ordeal of Owain".to_string() };
admire_art(art1);
admire_art(art1);
}
Inspect the failing program that attempts to pass the same artwork to admire_art twice. section 2.1
$ cargo run
error[E0382]: use of moved value: `art1`
--> src/main.rs:11:16
|
8 | let art1 = Artwork {};
| ---- move occurs because `art1` has type `Artwork`, which
| does not implement the `Copy` trait
9 |
10 | admire_art(art1);
| ---- value moved here
11 | admire_art(art1);
| ^^^^ value used here after move
error: aborting due to previous error; 1 warning emitted
Read the compiler diagnostic identifying the move, the later invalid use, and the missing Copy implementation. section 2.1
