Cannot move field of FnOnce

help
#1

Hi, I'm beginner to rust. Can any one explain why this snippet doesn't work? and what's the best practice to do the same thing?
struct Foo where F: FnOnce() {
f: F,
}

impl<T> Foo<T> where T: FnOnce() {
    fn new(f: T) -> Self {
        Foo {
            f
        }
    }
}

impl<F> Drop for Foo<F> where F: FnOnce() {
    fn drop(&mut self) {
        let y = self.f;  //error: cannot move
        y();
    }
}
#2

The problem here is that self.f will be dropped after the Drop::drop function is run when dropping. You can wrap f in an Option and then use self.f.take().unwrap() in the Drop impl. Option::take replaces the option with a None and returns the old value.

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