src/test/ui/issues/issue-24535-allow-mutable-borrow-in-match-guard.rs

   1 // run-pass
   2 // This test illustrates that under NLL, we can remove our overly
   3 // conservative approach for disallowing mutations of match inputs.
   4
   5 // See further discussion on rust-lang/rust#24535,
   6 // rust-lang/rfcs#1006, and rust-lang/rfcs#107
   7
   8 fn main() {
   9     rust_issue_24535();
  10     rfcs_issue_1006_1();
  11     rfcs_issue_1006_2();
  12 }
  13
  14 fn rust_issue_24535() {
  15     fn compare(a: &u8, b: &mut u8) -> bool {
  16         a == b
  17     }
  18
  19     let a = 3u8;
  20
  21     match a {
  22         0 => panic!("nope"),
  23         3 if compare(&a, &mut 3) => (),
  24         _ => panic!("nope"),
  25     }
  26 }
  27
  28 fn rfcs_issue_1006_1() {
  29     let v = vec!["1".to_string(), "2".to_string(), "3".to_string()];
  30     match Some(&v) {
  31         Some(iv) if iv.iter().any(|x| &x[..]=="2") => true,
  32         _ => panic!("nope"),
  33     };
  34 }
  35
  36 fn rfcs_issue_1006_2() {
  37     #[inline(always)]
  38     fn check<'a, I: Iterator<Item=&'a i32>>(mut i: I) -> bool {
  39         i.any(|&x| x == 2)
  40     }
  41
  42     let slice = [1, 2, 3];
  43
  44     match 42 {
  45         _ if slice.iter().any(|&x| x == 2) => { true },
  46         _ => { panic!("nope"); }
  47     };
  48
  49     // (This match is just illustrating how easy it was to circumvent
  50     // the checking performed for the previous `match`.)
  51     match 42 {
  52         _ if check(slice.iter()) => { true },
  53         _ => { panic!("nope"); }
  54     };
  55 }