How to enforce template parameter class to derive from super with an anonymous template parameter

Question

I have a couple of template classes

template < class Cost >
class Transition {
  public:
    virtual Cost getCost() = 0;
};

template < class Transition         


        

Answer 1

One way is to use the return type of getCost() (but it may give you an uglier error messgae if TransactionCl() doesn't have such a public member function).

std::is_base_of< Transition< decltype(TransitionCl().getCost()) >, TransitionCl >::value,

Another option is adding a typedef to the base class:

template < class Cost >
class Transition {
  public:
    typedef Cost Cost_Type;    // <-------
    virtual Cost getCost() = 0;
};

Then you can remove State's typename Cost parameter and use the typedef instead in your static assert...

std::is_base_of< Transition< typename TransitionCl::Cost_Type >, TransitionCl >::value,