lazy_ref_for_thunk.rs

impl<T> LazyRef for Thunk<T> {
    #[inline]
    fn defer<'a, F: FnBox() -> T + 'a>(f: F) -> Thunk<T>
        where T: 'a
    {
        let thunk =
            unsafe { Box::from_raw(Box::into_raw(Box::new(f)) as *mut (FnBox() -> T + 'static)) };

        Thunk {
            flag: Cell::new(Flag::Deferred),
            data: UnsafeCell::new(Cache { deferred: thunk }),
        }
    }


    #[inline]
    fn force(&self) {
        match self.flag.get() {
            Flag::Deferred => {
                unsafe {
                    (*self.data.get()).evaluate_thunk();
                }

                self.flag.set(Flag::Evaluated);
            }
            Flag::Evaluated => {}
            Flag::Empty => unsafe { unreachable() },
        }
    }
}

error[E0310]: the parameter type `F` may not live long enough
   --> src/unsync.rs:144:36
    |
144 |             unsafe { Box::from_raw(Box::into_raw(Box::new(f)) as *mut (FnBox() -> T + 'static)) };
    |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
    = help: consider adding an explicit lifetime bound `F: 'static`...
note: ...so that the type `F` will meet its required lifetime bounds
   --> src/unsync.rs:144:36
    |
144 |             unsafe { Box::from_raw(Box::into_raw(Box::new(f)) as *mut (FnBox() -> T + 'static)) };
    |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^