Template, inheritance, sizeof on incomplete type

[tni]

I'm trying to achieve the following:

template<int size>
class A {
};

class B : public A<sizeof(B)> {
};

This obviously doesn't work. Is there some reasonably clean template
magic to achieve this effect?

 

[Johannes Schaub (litb)]

I'm trying to achieve the following:

template<int size>
class A {
};

class B : public A<sizeof(B)> {
};

This obviously doesn't work. Is there some reasonably clean template
magic to achieve this effect?

It depends where you need "size". You may delay the sizeof application

template<typename D>
class A {
void f() { ... sizeof(D); ... }
};

Doing it that way is valid if "f" is instantiated at a point where "B" is
complete.