src/test/ui/regions/regions-variance-contravariant-use-covariant.rs

   1 // Test that a type which is covariant with respect to its region
   2 // parameter yields an error when used in a contravariant way.
   3 //
   4 // Note: see variance-regions-*.rs for the tests that check that the
   5 // variance inference works in the first place.
   6
   7 // This is contravariant with respect to 'a, meaning that
   8 // Contravariant<'long> <: Contravariant<'short> iff
   9 // 'short <= 'long
  10 struct Contravariant<'a> {
  11     f: &'a isize
  12 }
  13
  14 fn use_<'short,'long>(c: Contravariant<'short>,
  15                       s: &'short isize,
  16                       l: &'long isize,
  17                       _where:Option<&'short &'long ()>) {
  18
  19     // Test whether Contravariant<'short> <: Contravariant<'long>.  Since
  20     // 'short <= 'long, this would be true if the Contravariant type were
  21     // covariant with respect to its parameter 'a.
  22
  23     let _: Contravariant<'long> = c;
  24     //~^ ERROR lifetime may not live long enough
  25 }
  26
  27 fn main() {}