tests/ui/deriving/deriving-cmp-shortcircuit.rs

   1 // run-pass
   2 // check that the derived impls for the comparison traits shortcircuit
   3 // where possible, by having a type that panics when compared as the
   4 // second element, so this passes iff the instances shortcircuit.
   5
   6
   7 use std::cmp::Ordering;
   8
   9 pub struct FailCmp;
  10 impl PartialEq for FailCmp {
  11     fn eq(&self, _: &FailCmp) -> bool { panic!("eq") }
  12 }
  13
  14 impl PartialOrd for FailCmp {
  15     fn partial_cmp(&self, _: &FailCmp) -> Option<Ordering> { panic!("partial_cmp") }
  16 }
  17
  18 impl Eq for FailCmp {}
  19
  20 impl Ord for FailCmp {
  21     fn cmp(&self, _: &FailCmp) -> Ordering { panic!("cmp") }
  22 }
  23
  24 #[derive(PartialEq,PartialOrd,Eq,Ord)]
  25 struct ShortCircuit {
  26     x: isize,
  27     y: FailCmp
  28 }
  29
  30 pub fn main() {
  31     let a = ShortCircuit { x: 1, y: FailCmp };
  32     let b = ShortCircuit { x: 2, y: FailCmp };
  33
  34     assert!(a != b);
  35     assert!(a < b);
  36     assert_eq!(a.cmp(&b), ::std::cmp::Ordering::Less);
  37 }