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  1. #include <iostream>
  2. #include <type_traits>
  3. #include <typeinfo>
  4.  
  5. template <class T> struct type_printer { static void print() { std::cout << typeid(T).name(); } };
  6. template <class T> struct type_printer<T const> { static void print() { type_printer<T>::print(); std::cout << " const"; } };
  7. template <class T> struct type_printer<T*> { static void print() { type_printer<T>::print(); std::cout << " *"; } };
  8. template <class T> struct type_printer<T&> { static void print() { type_printer<T>::print(); std::cout << " &"; } };
  9.  
  10. #define printtype(...) type_printer<__VA_ARGS__>::print()
  11. #define printtype_line(...) do { std::cout << #__VA_ARGS__ ": " << std::endl; printtype(__VA_ARGS__); std::cout << std::endl; } while (0)
  12.  
  13. template<typename Derived>
  14. struct base
  15. {
  16.     void const_method() const
  17.     {
  18.         static_cast<Derived*>(this)->method();
  19.     }
  20.  
  21.     void fixed_const_method() const
  22.     {
  23.         // base<derived> const*
  24.         printtype_line(decltype(this));
  25.         // base<derived>
  26.         printtype_line(typename std::remove_pointer<decltype(this)>::type);
  27.         // base<derived>
  28.         printtype_line(decltype(*this));
  29.         // derived const*
  30.         printtype_line(typename std::conditional<
  31.                                 std::is_const<
  32.                                     typename std::remove_pointer<decltype(this)>::type>::value,
  33.                                 Derived const* const,
  34.                                 Derived* const>::type);
  35.  
  36.         static_cast<
  37.             typename std::conditional<
  38.                 std::is_const<
  39.                     typename std::remove_pointer<decltype(this)>::type>::value,
  40.                 Derived const* const,
  41.                 Derived* const>::type>(this)->method();
  42.     }
  43. };
  44.  
  45. struct derived : public base<derived>
  46. {
  47.     void method() const
  48.     {
  49.         std::cout << "const method" << std::endl;
  50.     }
  51.  
  52.     void method()
  53.     {
  54.         std::cout << "non-const method" << std::endl;
  55.     }
  56. };
  57.  
  58. int main()
  59. {
  60.     derived d;
  61.     d.fixed_const_method();
  62.  
  63.     return 0;
  64. }
Success #stdin #stdout 0s 2856KB
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decltype(this): 
4baseI7derivedE const *
typename std::remove_pointer<decltype(this)>::type: 
4baseI7derivedE const
decltype(*this): 
4baseI7derivedE const &
typename std::conditional< std::is_const< typename std::remove_pointer<decltype(this)>::type>::value, Derived const* const, Derived* const>::type: 
7derived const * const
const method
https://ideone.com/af993A
language:
C++14 (gcc 8.3)
created:
11 years ago
visibility:
secret

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