pub fn push(&mut self, key: K, val: V) {
        let len = self.len_mut();
        let idx = usize::from(*len);
        assert!(idx < CAPACITY);
        *len += 1;
        unsafe {
            self.key_area_mut(idx).write(key);
            self.val_area_mut(idx).write(val);
        }
    }
Unsafely asserts to the compiler the static information that this node is an `Internal`.
benchmarks/haystacks/code/rust-library.rs