Is it safe to implement a rwlock_filter_map

[lucassardois]

This crate: https://docs.rs/ref_filter_map/1.0.1/ref_filter_map/ allow to deal with guard and options using an unsafe operation.
The core of the crate is this code:

pub fn ref_filter_map<
    T: ?Sized,
    U: ?Sized,
    F: FnOnce(&T) -> Option<&U>
>(orig: Ref<T>, f: F) -> Option<Ref<U>> {
    f(&orig)
        .map(|new| new as *const U)
        .map(|raw| Ref::map(orig, |_| unsafe { &*raw }))
}

Would translating the previous code snipped to RwLock works safely?

pub fn rwlock_filter_map<
    T: ?Sized,
    U: ?Sized,
    F: FnOnce(&T) -> Option<&U>
>(orig: MappedRwLockReadGuard<T>, f: F) -> Option<MappedRwLockReadGuard<U>> {
    f(&orig)
        .map(|new| new as *const U)
        .map(|raw| MappedRwLockReadGuard::map(orig, |_| unsafe { &*raw }))
}