LYR-SEM0178

the value of a '@MustUse' call is dropped

warning · spec 11-metaprogramming · lint unused-result, group unused, warn unless said

An expression statement drops the non-void value of a call to a function marked @MustUse, or a value whose type is marked @MustUse (such as a Result or a task handle from std.task.spawn).

Explanation

@MustUse says that ignoring the value is almost always a mistake: a Result carries an error, a task handle is the only way to the task's error. A call written as a statement throws that value away without a word.

Use the value, or drop it on purpose with let _ = ….

Wrong

@MustUse
fn token(): int {
    return 7;
}

fn main(): void {
    token();
}

Right

@MustUse
fn token(): int {
    return 7;
}

fn main(): void {
    let _ = token();
}