Question

Ok, this is really difficult to confess, but I do have a strong temptation at the moment to inherit from std::vector.

I need about 10 customized algorithms for vector and I want them to be directly members of the vector. But naturally I want also to have the rest of std::vector‘s interface. Well, my first idea, as a law-abiding citizen, was to have an std::vector member in MyVector class. But then I would have to manually reprovide all of the std::vector’s interface. Too much to type. Next, I thought about private inheritance, so that instead of reproviding methods I would write a bunch of using std::vector::member‘s in the public section. This is tedious too actually.

And here I am, I really do think that I can simply inherit publicly from std::vector, but provide a warning in the documentation that this class should not be used polymorphically. I think most developers are competent enough to understand that this shouldn’t be used polymorphically anyway.

Is my decision absolutely unjustifiable? If so, why? Can you provide an alternative which would have the additional members actually members but would not involve retyping all of vector’s interface? I doubt it, but if you can, I’ll just be happy.

Also, apart from the fact that some idiot can write something like

std::vector<int>* p  = new MyVector

is there any other realistic peril in using MyVector? By saying realistic I discard things like imagine a function which takes a pointer to vector …

Well, I’ve stated my case. I have sinned. Now it’s up to you to forgive me or not 🙂

Answer 1

Actually, there is nothing wrong with public inheritance of std::vector. If you need this, just do that.

I would suggest doing that only if it is really necessary. Only if you can’t do what you want with free functions (e.g. should keep some state).

The problem is that MyVector is a new entity. It means a new C++ developer should know what the hell it is before using it. What’s the difference between std::vector and MyVector? Which one is better to use here and there? What if I need to move std::vector to MyVector? May I just use swap() or not?

Do not produce new entities just to make something to look better. These entities (especially, such common) aren’t going to live in vacuum. They will live in mixed environment with constantly increased entropy.