Comment by bluGill
5 hours ago
I'm not sure who invented "object oriented", but objects were invented by Simula in 1967 (or before, but first released then?) and that is where C++ takes the term from. Smalltalk-80 did some interesting things on top of objects that allow for object oriented programming.
In any case, Alan Kay is constantly clear that object oriented programming is about messages, which you can do in C++ in a number of ways. (I'm not sure exactly what Alan Kay means here, but it appears to exclude function calls, but would allow QT signal/slots)
The specific thing you can do in Smalltalk (or Ruby, Python, Objective-C, Erights E, or JS) that you can't do in C++ (even Qt C++, and not Simula either) is define a proxy class you can call arbitrary methods on, so that it can, for example, forward the method call to another object across the network, or deserialize an object stored on disk, or simply log all the methods called on a given object.
This is because, conceptually, the object has total freedom to handle the message it was sent however it sees fit. Even if it's never heard of the method name before.
You can do that in C++ too - it is just a lot of manual work. Those other languages just hide (or make easy) all the work needed to do that. There are trade offs though - just because you can in C++ doesn't mean you should: C++ is best where the performance cost of that is unacceptable.
No, in C++ it's literally impossible. The language provides no way to define a proxy class you can call arbitrary methods on. You have to generate a fresh proxy class every time you have a new abstract base class you want to interpose, either by hand, with a macro processor, or with run-time code generation. There's no language mechanism to compile code that calls .fhqwhgads() successfully on a class that doesn't have a .fhqwhgads() method declared.
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