quest – Rust: Moving out

Borrow checker Advanced

26 Moving out

You can't move a value out from behind a reference -- that would leave a hole. The fix is to swap something valid into its place and hand back the old value. std gives you take for exactly this.

Step 1 / 2

Fix take_at: return the String at index i, leaving an empty String behind. You can't move out of a Vec by indexing.

Hints

std::mem::take(&mut v[i]) swaps in String::default() (empty) and returns the old value.

26_move_out.rs

// BROKEN: `let s = v[i];` tries to move a String out of the Vec,
// leaving a hole. Run it to see the error, then use std::mem::take.
fn take_at(v: &mut Vec<String>, i: usize) -> String {
    let s = v[i];
    s
}

Reset to starterCompiled in a sandbox; hidden checks must pass.

Reveal solution

fn take_at(v: &mut Vec<String>, i: usize) -> String {
    std::mem::take(&mut v[i])
}