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// Various unsuccessful attempts to put the unboxed closure kind
// inference into an awkward position that might require fixed point
// iteration (basically where inferring the kind of a closure `c`
// would require knowing the kind of `c`). I currently believe this is
// impossible.
fn a() {
// This case of recursion wouldn't even require fixed-point
// iteration, but it still doesn't work. The weird structure with
// the `Option` is to avoid giving any useful hints about the `Fn`
// kind via the expected type.
let mut factorial: Option<Box<dyn Fn(u32) -> u32>> = None;
let f = |x: u32| -> u32 {
let g = factorial.as_ref().unwrap();
//~^ ERROR `factorial` does not live long enough
if x == 0 {1} else {x * g(x-1)}
};
factorial = Some(Box::new(f));
//~^ ERROR cannot assign to `factorial` because it is borrowed
}
fn b() {
let mut factorial: Option<Box<dyn Fn(u32) -> u32 + 'static>> = None;
let f = |x: u32| -> u32 {
let g = factorial.as_ref().unwrap();
//~^ ERROR `factorial` does not live long enough
if x == 0 {1} else {x * g(x-1)}
};
factorial = Some(Box::new(f));
//~^ ERROR cannot assign to `factorial` because it is borrowed
}
fn main() { }
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