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//@ run-pass
// Demonstrate the use of the unguarded escape hatch with a trait bound
// to assert that destructor will not access any dead data.
//
// Compare with ui/span/issue28498-reject-trait-bound.rs
#![feature(dropck_eyepatch)]
use std::fmt;
#[derive(Debug)]
struct ScribbleOnDrop(String);
impl Drop for ScribbleOnDrop {
fn drop(&mut self) {
self.0 = format!("DROPPED");
}
}
struct Foo<T: fmt::Debug>(u32, T);
unsafe impl<#[may_dangle] T: fmt::Debug> Drop for Foo<T> {
fn drop(&mut self) {
// Use of `may_dangle` is sound, because destructor never accesses
// the `Debug::fmt` method of `T`, despite having it available.
println!("Dropping Foo({}, _)", self.0);
}
}
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);
foo1 = Foo(1, &first_dropped);
println!("foo0.1: {:?} foo1.1: {:?}", foo0.1, foo1.1);
}
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