tests/ui/dropck/issue-28498-ugeh-with-lifetime-param.rs

   1 // run-pass
   2
   3 // Demonstrate the use of the unguarded escape hatch with a lifetime param
   4 // to assert that destructor will not access any dead data.
   5 //
   6 // Compare with ui/span/issue28498-reject-lifetime-param.rs
   7
   8 #![feature(dropck_eyepatch)]
   9
  10 #[derive(Debug)]
  11 struct ScribbleOnDrop(String);
  12
  13 impl Drop for ScribbleOnDrop {
  14     fn drop(&mut self) {
  15         self.0 = format!("DROPPED");
  16     }
  17 }
  18
  19 struct Foo<'a>(u32, &'a ScribbleOnDrop);
  20
  21 unsafe impl<#[may_dangle] 'a> Drop for Foo<'a> {
  22     fn drop(&mut self) {
  23         // Use of `may_dangle` is sound, because destructor never accesses `self.1`.
  24         println!("Dropping Foo({}, _)", self.0);
  25     }
  26 }
  27
  28 fn main() {
  29     let (last_dropped, foo0);
  30     let (foo1, first_dropped);
  31
  32     last_dropped = ScribbleOnDrop(format!("last"));
  33     first_dropped = ScribbleOnDrop(format!("first"));
  34     foo0 = Foo(0, &last_dropped);
  35     foo1 = Foo(1, &first_dropped);
  36
  37     println!("foo0.1: {:?} foo1.1: {:?}", foo0.1, foo1.1);
  38 }