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by moth-fuzz
1099 days ago
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One thing that's bothered me for a few years about Object-Oriented code, is the question of why the dichotomy of 'implementation' vs 'interface' is drawn on the exact same line as 'variables' and 'functions'. Everyone who's ever worked in a functional programming languages knows that functions can easily be considered 'state', and everybody who's spent time in real-life plugging in various electronic devices knows that data itself can be considered an 'interface'. So why does OOP dogma conflate these ideas together? Why couldn't a single variable or property be virtual and polymorphic? Why couldn't a member method be reassignable like a member variable? The philosophy and the actual implementations just self-reference each other. Interfaces are great because they keep interfaces separate from state. I agree. But strictly in terms of language features, why are functions considered interface while variables are considered state? Well, because that's just how they're defined, I guess. But if you're doing OOP in C, and you have a VTABLE full of pointers, well, it doesn't really matter what those pointers point do, do they? They could be function pointers, they could be variables/memory locations, they could even be references to other structs. It's not quite as delineated when you do it from the bottom up. |
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> the dichotomy of 'implementation' vs 'interface' is drawn on the exact same line as 'variables' and 'functions'.
That's not true; They are orthogonal to each other.
OOP is just a way of structuring Procedural/Imperative programming; "variables" maintain state while "functions" change/read state. You are just bundling them together to gain fine-grained modularity. An "interface" is anything (i.e. can be both variables and functions) which is "publicly" accessible by a client. An "implementation" is conversely not accessible by the client (i.e. encapsulated) but can also consist of "variables" and "functions".
> Why couldn't a single variable or property be virtual and polymorphic?
Not sure what you mean here but you do have tagged unions/variants/sum types which gives you what you maybe looking for.
> Why couldn't a member method be reassignable like a member variable?
It is possible in certain object models. Lookup "Metaclasses" in your favourite language for possible support. If you want to see example code in C++, checkout the classic Advanced C++ Programming Styles and Idioms by James Coplien. The book contains lots of examples of mind-bending OO trickery using C++.