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#![feature(fn_traits, unboxed_closures)]
use std::marker::PhantomData;
// An erroneous variant of `run-pass/unboxed_closures-infer-recursive-fn.rs`
// where we attempt to perform mutation in the recursive function. This fails to compile
// because it winds up requiring `FnMut` which enforces linearity.
struct YCombinator<F,A,R> {
func: F,
marker: PhantomData<(A,R)>,
}
impl<F,A,R> YCombinator<F,A,R> {
fn new(f: F) -> YCombinator<F,A,R> {
YCombinator { func: f, marker: PhantomData }
}
}
impl<A,R,F : FnMut(&mut dyn FnMut(A) -> R, A) -> R> FnMut<(A,)> for YCombinator<F,A,R> {
extern "rust-call" fn call_mut(&mut self, (arg,): (A,)) -> R {
(self.func)(self, arg)
//~^ ERROR cannot borrow `*self` as mutable more than once at a time
}
}
impl<A,R,F : FnMut(&mut dyn FnMut(A) -> R, A) -> R> FnOnce<(A,)> for YCombinator<F,A,R> {
type Output = R;
extern "rust-call" fn call_once(mut self, args: (A,)) -> R {
self.call_mut(args)
}
}
fn main() {
let mut counter = 0;
let factorial = |recur: &mut dyn FnMut(u32) -> u32, arg: u32| -> u32 {
counter += 1;
if arg == 0 {1} else {arg * recur(arg-1)}
};
let mut factorial: YCombinator<_,u32,u32> = YCombinator::new(factorial);
let mut r = factorial(10);
assert_eq!(3628800, r);
}
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