That's really odd. I have a Sketch with a pure virtual function...
class TrdApplication
{
public:
virtual void Run( bool& OkToSleep ) = 0;
};
...and I haven't had any problems.
I prefer declarations and code separated so that might make a difference.
The compiler / linker must think that you've created an instance of DebouncedButton.
Oh well. I'm glad you found a solution.
- Brian