mirror of https://github.com/rust-lang/rust
67 lines
1.6 KiB
Rust
67 lines
1.6 KiB
Rust
//@ 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>>>());
|
|
}
|