1 // Various unsuccessful attempts to put the unboxed closure kind
2 // inference into an awkward position that might require fixed point
3 // iteration (basically where inferring the kind of a closure `c`
4 // would require knowing the kind of `c`). I currently believe this is
5 // impossible.
6
a()7 fn a() {
8 // This case of recursion wouldn't even require fixed-point
9 // iteration, but it still doesn't work. The weird structure with
10 // the `Option` is to avoid giving any useful hints about the `Fn`
11 // kind via the expected type.
12 let mut factorial: Option<Box<dyn Fn(u32) -> u32>> = None;
13
14 let f = |x: u32| -> u32 {
15 let g = factorial.as_ref().unwrap();
16 //~^ ERROR `factorial` does not live long enough
17 if x == 0 {1} else {x * g(x-1)}
18 };
19
20 factorial = Some(Box::new(f));
21 //~^ ERROR cannot assign to `factorial` because it is borrowed
22 }
23
b()24 fn b() {
25 let mut factorial: Option<Box<dyn Fn(u32) -> u32 + 'static>> = None;
26
27 let f = |x: u32| -> u32 {
28 let g = factorial.as_ref().unwrap();
29 //~^ ERROR `factorial` does not live long enough
30 if x == 0 {1} else {x * g(x-1)}
31 };
32
33 factorial = Some(Box::new(f));
34 //~^ ERROR cannot assign to `factorial` because it is borrowed
35 }
36
main()37 fn main() { }
38