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// run-pass
// Demonstrate the use of the unguarded escape hatch with a type param in negative position
// to assert that destructor will not access any dead data.
// Compare with compile-fail/
// Demonstrate that a type param in negative position causes dropck to reject code
// that might indirectly access previously dropped value.
// Compare with run-pass/
struct ScribbleOnDrop(String);
impl Drop for ScribbleOnDrop {
fn drop(&mut self) {
self.0 = format!("DROPPED");
struct Foo<T>(u32, T, Box<for <'r> fn(&'r T) -> String>);
unsafe impl<#[may_dangle] T> Drop for Foo<T> {
fn drop(&mut self) {
// Use of `may_dangle` is sound, because destructor never passes a `self.1`
// to the callback (in `self.2`) despite having it available.
println!("Dropping Foo({}, _)", self.0);
fn callback(s: & &ScribbleOnDrop) -> String { format!("{:?}", s) }
fn main() {
let (last_dropped, foo0);
let (foo1, first_dropped);
last_dropped = ScribbleOnDrop(format!("last"));
first_dropped = ScribbleOnDrop(format!("first"));
foo0 = Foo(0, &last_dropped, Box::new(callback));
foo1 = Foo(1, &first_dropped, Box::new(callback));
println!("foo0.1: {:?} foo1.1: {:?}", foo0.1, foo1.1);
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