dropping

drop.rs

//
// Option1 - Explicit destruction
//
struct A;
struct B;

impl A {
    fn shutdown(self) {
        println!("Do some destruction");
    }
}

impl Drop for A {
    fn drop(&mut self) {
        panic!("You must have called shutdown() before")
    }
}

impl B {
    fn shutdown(self) {
        println!("Do some destruction");
    }
}

impl Drop for B {
    fn drop(&mut self) {
        panic!("You must have called shutdown() before")
    }
}

struct S {
    a: Option<A>,
    b: Option<B>
}

impl S {
    fn shutdown(mut self) {
        self.a.take().unwrap().shutdown();
        self.b.take().unwrap().shutdown();
    } 
}

impl Drop for S {
    fn drop(&mut self) {
        panic!("You must have called shutdown() before")
    }
}

//
// Option2 - Implicit destruction
//
struct A_;
struct B_;

impl Drop for A_ {
    fn drop(&mut self) {
        println!("Do some destruction");
    }
}

impl Drop for B_ {
    fn drop(&mut self) {
        println!("Do some destruction");
    }
}

struct S_ {
    a: A_,
    b: B_,
}

// no need to impl Drop for S_