Can I use a slim version of my header to be included with the library?

Question

What I mean is my real header file can look like this:

#include "some_internal_class.h"

class MyLibrary {
    Type private_member;

    void private_function();
public:

    MyLibrary();
    void function_to_be_called_by_library_users();
};

Now I want to produce a dynamic library containing all the necessary definitions. and I want to ship with it a single header instead of shipping every single header I have in my library.

So I was thinking I could create a slim version of my header like so:

class MyLibrary {
public:     
    MyLibrary();
    void function_to_be_called_by_library_users();
};

Headers are just declarations anyway right? they're never passed to the compiler. And I've declared what the user will be using.

Is that possible? If not, why not?

Answer 1

This is a One Definition Rule violation. The moment you deviate by a single token.

[basic.def.odr]/6

There can be more than one definition of a class type, [...] in a program provided that each definition appears in a different translation unit, and provided the definitions satisfy the following requirements. Given such an entity named D defined in more than one translation unit, then

• each definition of D shall consist of the same sequence of tokens; and

Your program may easily break if you violate the ODR like that. And your build system isn't at all obligated to even warn you about it.

Answer 2

You cannot define a class twice. It breaks the One Definition Rule (ODT). MyLibrary does that, unfortunately.

they're never passed to the compiler

They will. Members of a class must be known at compile time, so that the compiler can determine the class's size.