Why we need to copy-and-paste functions declaration into inherited class header

Question

This is for C++.

Usually we have our function declaration in header file and definition in source file. Say we have a class A with some functions:

//< A.hpp
class A
{
public:
   virtual funcA();
   virtual funcB();
}

And we want to have a class inherit from A and override its functions.

//< childA.hpp
class childA
{
   virtual funcA();
   virtual funcB();
}

Everytime we change the declarations of funcA() funcB(), we need to copy-and-paste the new declarations to the child classes header files. If the inheritance chain is long, it's quite bother.

I remember we don't have this problem with Object-C, do we?

Answer 1

You don't need to copy a member function declaration to the child class's header file unless you want to override it. In that case, I believe the main reason you're required to declare it is to inform anyone reading your header file that the child class is providing a different implementation. In principle, the compiler can figure it out automatically, but it could be a real pain for a human to do the same thing manually.

Note that in many cases, people reading your header files may not have access to the actual source code for the body (e.g., if it's a proprietary library that is delivered to them as compiled objects), so they can't just go look at the body to figure it out.

Answer 2

From the Objective-C article on Wikipedia:

Objective-C, like Smalltalk, can use dynamic typing: an object can be sent a message that is not specified in its interface.

http://en.wikipedia.org/wiki/Type_system#Dynamic_typing

C++, on the other hand, is statically typed. It's a stricter compile-time restraint.