Electronic – C++ classes for I/O pin abstraction

I am looking for C++ abstractions for hardware I/O points or pins. Things like in_pin, out_pin, inout_pin, maybe open_collector_pin, etc.

I surely can come up with such a set of abstractions myself, so I am not looking for 'hey, you might do it this way' type of answers, but rather the 'look at this library that has been used in this and this and this project'.

Google did not turn up anything, maybe because I don't know how others would call this.

My aim is to build I/O libraries that are based on such points, but also provide such points, so it would be easy to for instance connect an HD44780 LCd to either the IO pins of the chip, or an I2C (or SPI) I/O extender, or any other point that can somehow be controlled, without any change to the LCD class.

I know this is on the electronics/software edge, sorry if it does not belong here.

@leon: wiring
That is a big bag of software, I will need to look closer. But is seems they do not use a pin abstraction like I want. For instance in the keypad implementation I see

digitalWrite(columnPins[c], LOW);   // Activate the current column.

This implies that there is one function (digitalWrite) that knows how to write to an I/O pin. This makes it impossible to add a new type of I/O pin (for instance one that is on an MCP23017, so it has to be written via I2C) without rewriting the digitalWrite function.

@Oli: I googled an Arduino IO example, but the seem to use about the same approach as the Wiring library:

int ledPin = 13;                 // LED connected to digital pin 13
void setup(){
    pinMode(ledPin, OUTPUT);      // sets the digital pin as output
}