If you are doing this for a Linux platform, there's actually a gpio matrix keypad driver that works really well. The driver shows up as a regular keyboard input device that can interface with any program that knows how to read /dev/input things.
I do not like the idea of sending an interrupt and cause a havoc on OS side every time two metal plates bounce off each other.
I can understand this when this happens to a device that is created to monitor the switch (switch matrix controller, keyboard controller, etc.) but when this happens to a machine that may have something more important to do it feels at the very least inelegant.
Agreed, just as encapsulation/abstraction is an important and indispensible concept in software engineering, it is also equally if not more critical in hardware applications. For most electronics, there is usually an IC that can solve a problem better than you can develop, often cheaper. 25 discrete components can be encapsulated by a single IC sometimes (with a couple of bypass caps).
