pub fn map_ref<T, U>(
    v: RwLockReadGuard<'_, RawRwLock, T>,
    f: impl FnOnce(&T) -> &U
) -> MappedRwLockReadGuard<'_, RawRwLock, U>where
    U: ?Sized,
Expand description

Map a read guard into a sub-type it contains.