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//@ run-pass
#![allow(dead_code)]
use std::mem::needs_drop;
use std::mem::ManuallyDrop;
struct NeedDrop;
impl Drop for NeedDrop {
fn drop(&mut self) {}
}
// Constant expressios allow `NoDrop` to go out of scope,
// unlike a value of the interior type implementing `Drop`.
static X: () = (NoDrop { inner: ManuallyDrop::new(NeedDrop) }, ()).1;
const Y: () = (NoDrop { inner: ManuallyDrop::new(NeedDrop) }, ()).1;
const fn _f() {
(NoDrop { inner: ManuallyDrop::new(NeedDrop) }, ()).1
}
// A union that scrubs the drop glue from its inner type
union NoDrop<T> {
inner: ManuallyDrop<T>,
}
// Copy currently can't be implemented on drop-containing unions,
// this may change later
// https://github.com/rust-lang/rust/pull/38934#issuecomment-271219289
// // We should be able to implement Copy for NoDrop
// impl<T> Copy for NoDrop<T> {}
// impl<T> Clone for NoDrop<T> {fn clone(&self) -> Self { *self }}
// // We should be able to implement Copy for things using NoDrop
// #[derive(Copy, Clone)]
struct Foo {
x: NoDrop<Box<u8>>,
}
struct Baz {
x: NoDrop<Box<u8>>,
y: Box<u8>,
}
union ActuallyDrop<T> {
inner: ManuallyDrop<T>,
}
impl<T> Drop for ActuallyDrop<T> {
fn drop(&mut self) {}
}
fn main() {
// NoDrop should not make needs_drop true
assert!(!needs_drop::<Foo>());
assert!(!needs_drop::<NoDrop<u8>>());
assert!(!needs_drop::<NoDrop<Box<u8>>>());
// presence of other drop types should still work
assert!(needs_drop::<Baz>());
// drop impl on union itself should work
assert!(needs_drop::<ActuallyDrop<u8>>());
assert!(needs_drop::<ActuallyDrop<Box<u8>>>());
}
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