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trait Foo {} struct Bar; static mut DROP_CALLED: bool = false; impl Drop for Bar { fn drop(&mut self) { unsafe { DROP_CALLED = true; } } } impl Foo for Bar {} use std::rc::Rc; fn main() { let b: Rc<dyn Foo> = Rc::new(Bar); assert!(unsafe { !DROP_CALLED }); drop(b); assert!(unsafe { DROP_CALLED }); }