Re: Calling a non-virtual member function for a NULL instance

Ivan Kolev wrote:


Yes, more or less. The basic idea is to implement the static function
for each derived class, then use a CRTP-based idiom to "automatically"
implement the virtual version. For example:

   #include <iostream>

   struct base {
      virtual int info() = 0;
      virtual ~base() {};
   };

   template <class T>
   struct base_impl: public base {
      virtual int info() { return T::information(); }
   };

   struct derived1: public base_impl<derived1> {
      static int information() { return 1; }
   };

   struct derived2: public base_impl<derived2> {
      static int information() { return 2; }
   };

   int main()
   {
      base* p1 = new derived1;
      base* p2 = new derived2;

      std::cout << p1->info()
                << ", "
                << p2->info()
                << '\n';
      std::cout << derived1::information()
                << ", "
                << derived2::information()
                << std::endl;
   }

The derived classes derive from base_impl<> instead of deriving
directly from base. base_impl<> provides the required override of the
virtual function, which simply calls the correct static function.

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