Template specialization based on inherit class

Question

I want to make this specialized w/o changing main. Is it possible to specialize something based on its base class? I hope so.

-edit-

I\'ll have several class

Answer 1

This article describes a neat trick: http://www.gotw.ca/publications/mxc++-item-4.htm

Here's the basic idea. You first need an IsDerivedFrom class (this provides runtime and compile-time checking):

template
class IsDerivedFrom
{
  class No { };
  class Yes { No no[3]; }; 

  static Yes Test( B* ); // not defined
  static No Test( ... ); // not defined 

  static void Constraints(D* p) { B* pb = p; pb = p; } 

public:
  enum { Is = sizeof(Test(static_cast(0))) == sizeof(Yes) }; 

  IsDerivedFrom() { void(*p)(D*) = Constraints; }
};

Then your MyClass needs an implementation that's potentially specialized:

template
class MyClassImpl
{
  // general case: T is not derived from SomeTag
}; 

template
class MyClassImpl
{
  // T is derived from SomeTag
  public:
     typedef int isSpecialized;
}; 

and MyClass actually looks like:

template
class MyClass: public MyClassImpl::Is>
{
};

Then your main will be fine the way it is:

int main()
{
    MyClass::isSpecialized test1; //ok
    MyClass::isSpecialized test2; //ok also
    return 0;
}