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