Encoder as PIDSource

[jwakeman]

WPILib question.

Is there a reason that the Encoder class doesn't implement the PIDSource interface? I see that it includes the header file but it doesn't actually inherit from PIDSource. Is this just a "TODO" for the lib or is there something fundamental that prevents using an encoder as PIDSource?

I'm asking because I was thinking we might want to use a PIDController to control the position of a "elevator" on our robot. Example, I might have a victor (the PIDOutput) that controls a motor for a chain drive that moves the elevator up and down and an encoder that tells me when i have reached my desired position.