This technique predates object oriented programming. It is called an abstract data type or data abstraction. A key difference between data abstraction and object oriented programming is that you can leave functions unimplemented in your abstract data type while OOP requires that the functions always be implemented.

The sanest way to have optional functions in object oriented programming that occurs to me would be to have an additional class for each optional function and inherit each one you implement alongside your base class via multiple inheritance. Then you would need to check at runtime whether the object is an instance of the additional class before using an optional function. With an abstract data type, you would just be do a simple NULL check to see if the function pointer is present before using it.

I personally don't like implicit this. You are very much passing a this instance around, as opposed to a class method. Also explicit this eliminates the problem, that you don't know if the variable is an instance variable or a global/from somewhere else.

I wrote about this concept[1] for my own understanding as well -- just tracing the an instance of the pattern through the tmux code.

[0] https://raw.githubusercontent.com/tmux/tmux/1536b7e206e51488... [1] https://blog.drnll.com/tmux-obj-oriented-commands