Trying to get familiar with Rust's pointers and closures by implementing a thunk data type

thunk-fail

enum ThunkData<T> {
    Val (T),
    Fun (~fn() -> T)
}
 
struct Thunk<T> {
    thunkData: ThunkData<T>
}
 
impl<T : Clone> Thunk<T> {
    fn force (&mut self) -> &T {
        match self.thunkData {
            Val (x) => return x,
            Fun (f) => {
                let x = f ();
                self.thunkData = Val (x);
                return x;
            }
        }
    }
}