src/test/ui/borrowck/borrow-immutable-upvar-mutation.rs

   1 #![feature(unboxed_closures)]
   2
   3 // Tests that we can't assign to or mutably borrow upvars from `Fn`
   4 // closures (issue #17780)
   5
   6 fn set(x: &mut usize) {
   7     *x = 5;
   8 }
   9
  10 fn to_fn<A, F: Fn<A>>(f: F) -> F {
  11     f
  12 }
  13 fn to_fn_mut<A, F: FnMut<A>>(f: F) -> F {
  14     f
  15 }
  16
  17 fn main() {
  18     // By-ref captures
  19     {
  20         let mut x = 0;
  21         let _f = to_fn(|| x = 42); //~ ERROR cannot assign
  22
  23         let mut y = 0;
  24         let _g = to_fn(|| set(&mut y)); //~ ERROR cannot borrow
  25
  26         let mut z = 0;
  27         let _h = to_fn_mut(|| {
  28             set(&mut z);
  29             to_fn(|| z = 42); //~ ERROR cannot assign
  30         });
  31     }
  32
  33     // By-value captures
  34     {
  35         let mut x = 0;
  36         let _f = to_fn(move || x = 42); //~ ERROR cannot assign
  37
  38         let mut y = 0;
  39         let _g = to_fn(move || set(&mut y)); //~ ERROR cannot borrow
  40
  41         let mut z = 0;
  42         let _h = to_fn_mut(move || {
  43             set(&mut z);
  44             to_fn(move || z = 42);
  45             //~^ ERROR cannot assign
  46         });
  47     }
  48 }
  49
  50 fn foo() -> Box<dyn Fn() -> usize> {
  51     let mut x = 0;
  52     Box::new(move || {
  53         x += 1; //~ ERROR cannot assign
  54         x
  55     })
  56 }