LYR-SEM0158

a place outlives the call that handed it over

error · spec 03-types

A coroutine function or a generator lambda takes a place parameter, or a lambda captures a place parameter.

Explanation

A place belongs to the call and ends with it. A coroutine's or generator's body runs after the call that created it has returned, and a lambda may be called after the function it was made in has returned, so neither may hold the caller's place.

Take the parameter by value, or read the place into a local and capture or yield that.

Wrong

fn counts(&n: int): Coroutine<int> {
    yield n;
}

fn main(): void {
    var x = 1;
    let _ = counts(&x);
}

Right

fn counts(n: int): Coroutine<int> {
    yield n;
}

fn main(): void {
    let x = 1;
    let _ = counts(x);
}