Myujth

I have two classes A and B like below, B have to inherit from A. The classType() function of class B is not provided, If call B::classType(), will get the class type of A. I would like to get a compiler error here instead of calling into the classType() function of class A. How do I do it?

In general, the sub classes of A should provide the function classType(), in case the author forgets to write the classType() function, it's best to report a compiler error. This is the purpose. Maybe, I can use static_assert in TypeOf() function.

class A

public:
 static const char* classType()
 
 static const char* s_classType = "A";
 return s_classType;
 
;

class B : public A

;

template <class T>
const char* TypeOf()

 return T::classType();


int main()

 const char* type = TypeOf<B>(); // I would like to get compiler error here, not get "A".

Alternatively, make A::classType() private in B:

class B : public A 
private:
 using A::classType;

Edit. After the question has been clarified, I suggest that you use type traits technique instead of static member functions.

template<class>
struct Traits;

template<>
struct Traits<A> 
 static const char* classType() 
 return "A";
 
;

template<class T>
const char* TypeOf() 
 return Traits<T>::classType();

Now the user has to define his own type trait for B, otherwise

const char* type = TypeOf<B>(); 

will not compile.

Apart from a couple of typos in your code ... add the following to the definition of class B

static const char* classType() = delete;

Live Demo

I got the idea from @Evg, thanks Evg.
Use template like below:

class A

public:
 template <class T>
 static const char* classType() static_assert(false, "classType not implemented"); 
 template <>
 static const char* classType<A>()
 
 static const char* s_classType = "A";
 return s_classType;
 
;

template <class T>
const char* TypeOf()

 return T::classType<T>();

Declare the function as pure virtual.

class A

public:
 virtual static const char* classType() =0;
;

Then all instantiated classes inheriting from A have to implement this.