Idea: `let _ = ` vs `_ = `

[ChayimFriedman2]

Discovered today: both let _ = and _ = (destructuring assignment) can be used to ignore #[must_use], however because the former is a statement while the latter is an expression they have a difference with temporary lifetime extension:

struct NoisyDrop;
impl Drop for NoisyDrop {
    fn drop(&mut self) {
        println!("NoisyDrop drop");
    }
}

fn main() {
    let _ = &NoisyDrop;
    println!("after");
}

Prints:

after
NoisyDrop drop

While:

struct NoisyDrop;
impl Drop for NoisyDrop {
    fn drop(&mut self) {
        println!("NoisyDrop drop");
    }
}

fn main() {
    _ = &NoisyDrop;
    println!("after");
}

Prints:

NoisyDrop drop
after