Question

I have a class Foo which is used in a small standalone project. It has a class definition in Foo.h with the implementation for the class’ member functions in an implementation file Foo.cpp.

First question – one of the member functions of class Foo is a template method Foo::doSomething(), is it correct that the implementation of this method should appear with the declaration of the function in Foo.h ?

The template parameter which Foo::doSomething() will be instantiated with is one of two Functor types – class CalcA and CalcB.

Should I:

• (A) put the defintion and implementation of the two Functor classes all together in Foo.cpp (where they are actually used by the implementation of other Foo member functions to call Foo::doSomething).
• (B) put the definition and implementation of the two Functor classes in Foo.h.
• (C) should I put split the definition and implementation of the two Functors across Foo.h and Foo.cpp as would be done with an ordinary class?

Answer 1

General rule:

If foo::doSomething() is used outside foo.cpp (i.e. if it’s public or protected, usually), it must go in the header.

If not, putting in in the cpp file is perfectly ok, and even a good idea (as it keeps the clutter away from the header file).

So, if the functors are only used in the cpp file, by all means put the template function there too. One can always refactor things later if this changes.