fork download 
  1. #include <iostream>
  2.  
  3.     class Base {
  4.     public:
  5.       template <typename To>
  6.       bool isa() const {
  7.         return this->match(To::GetID());
  8.       }
  9.  
  10.     protected:
  11.       typedef size_t ID;
  12.  
  13.       static ID NextID() { static ID id = 0; return id++; }
  14.  
  15.       virtual bool match(ID) const { return false; }
  16.     };
  17.  
  18.     class Derived: public Base {
  19.     public:
  20.       static ID GetID() { static ID id = NextID(); return id; }
  21.  
  22.     protected:
  23.       virtual bool match(ID id) const { return id == GetID() || Base::match(id); }
  24.     };
  25.  
  26.     class MostDerived: public Derived {
  27.     public:
  28.       static ID GetID() { static ID id = NextID(); return id; }
  29.  
  30.     protected:
  31.       virtual bool match(ID id) const { return id == GetID() || Derived::match(id); }
  32.     };
  33.  
  34.     template <typename To, typename From>
  35.     To const* dyn_cast(From const* f) {
  36.       if (f and f->template isa<To>()) { return static_cast<To const*>(f); }
  37.       return 0;
  38.     }
  39.  
  40.     template <typename To, typename From>
  41.     To* dyn_cast(From* f) { return const_cast<To*>(dyn_cast<To>((From const*)f)); }
  42.  
  43. int main() {
  44.   Derived derived; MostDerived mostDerived;
  45.   Base* d = &derived, * md = &mostDerived;
  46.  
  47.   if (dyn_cast<Derived>(d)) { std::cout << "Derived -> Derived: ok\n"; }
  48.   else                      { std::cout << "Derived -> Derived: ko\n"; }
  49.  
  50.   if (dyn_cast<MostDerived>(md)) { std::cout << "MostDerived -> MostDerived : ok\n"; }
  51.   else                           { std::cout << "MostDerived -> MostDerived : ko\n"; }
  52.  
  53.   if (dyn_cast<Derived>(md)) { std::cout << "MostDerived -> Derived : ok\n"; }
  54.   else                       { std::cout << "MostDerived -> Derived : ko\n"; }
  55.  
  56.   if (dyn_cast<MostDerived>(d)) { std::cout << "Derived -> MostDerived: ko\n"; }
  57.   else                          { std::cout << "Derived -> MostDerived: ok\n"; }
  58. }
Success #stdin #stdout 0.02s 2724KB
comments (?)
stdin 
Standard input is empty
stdout 
Derived -> Derived: ok
MostDerived -> MostDerived : ok
MostDerived -> Derived : ok
Derived -> MostDerived: ok
https://ideone.com/yxPd3
language:
C++ (gcc 8.3)
created:
14 years ago
visibility:
public

Share or Embed source code

Discover > Sphere Engine API

The brand new service which powers Ideone!

Discover > IDE Widget

Widget for compiling and running the source code in a web browser!