It is a work in progress. I build what I need but make sure I can extend later.
BTW: there is a method enableInternalPullup on the DigitalInput class 
I've created these classes as an exercise (in Arduino dependency management ) and because I don't like all the static and sequential stuff that seems to be the norm. I understand that it is convenient for beginners, but I am an OO programmer 8) and like it when I don't have to keep all the low level details in my head XD I truly believe that you get better code if you use OO responsibly. But I also understand that it is not the only variable on a platform like the Arduino. That is why I want to learn a bit more on code optimization first, before getting too far ahead of myself. 
Also being a beginner in experimenting with the Arduino (although I had previous experience with other types of MCU's) I quickly found that I was repeating myself (in code). To me, that is always a sign 'something needs to be done'. This is my first pass at it.
I hope more people will see its value and find these classes useful.