src/test/ui/regions/regions-ret-borrowed.rs

   1 // Ensure that you cannot use generic types to return a region outside
   2 // of its bound.  Here, in the `return_it()` fn, we call with() but
   3 // with R bound to &isize from the return_it.  Meanwhile, with()
   4 // provides a value that is only good within its own stack frame. This
   5 // used to successfully compile because we failed to account for the
   6 // fact that fn(x: &isize) rebound the region &.
   7
   8 fn with<R, F>(f: F) -> R where F: FnOnce(&isize) -> R {
   9     f(&3)
  10 }
  11
  12 fn return_it<'a>() -> &'a isize {
  13     with(|o| o)
  14     //~^ ERROR lifetime may not live long enough
  15 }
  16
  17 fn main() {
  18     let x = return_it();
  19     println!("foo={}", *x);
  20 }