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  1. template<class T, template<class> class Functor>
  2. class FunctorInterface_1 {
  3.    private:
  4.       const Functor<T> &f_cref;
  5.    public:
  6.       FunctorInterface_1() : f_cref(static_cast<const Functor<T>&>(*this)) {}
  7.       T operator() ( T val ) const { return f_cref(val); }
  8. }; // FunctorInterface_1 (works)
  9.  
  10. // Declare a traits class.
  11. template <typename T> struct FunctorTraits;
  12.  
  13. template<class Functor>
  14. class FunctorInterface_2 {
  15.    private:
  16.       const Functor &f_cref;
  17.    public:
  18.  
  19.       // Use the traits class to define Ftype
  20.       using Ftype = typename FunctorTraits<Functor>::type;
  21.  
  22.       FunctorInterface_2() : f_cref(static_cast<const Functor&>(*this)) {}
  23.       Ftype operator() ( Ftype val ) const { return f_cref(val); }
  24. }; // FunctorInterface_2 (no type in Functor!)
  25.  
  26. // Forward declare Cube to specialize FunctorTraits
  27. template<class T> struct Cube;
  28.  
  29. // Specialize FunctorTraits for Cube
  30. template <typename T> struct FunctorTraits<Cube<T>>
  31. {
  32.    using type = T; 
  33. };
  34.  
  35. template<class T>
  36. struct Cube : public FunctorInterface_2<Cube<T>> {
  37.    using type = T; 
  38.    T operator() ( T val ) const { return val*val*val; }
  39. }; // Cube
  40.  
  41. int main()
  42. {
  43.    Cube<int> a;
  44. }
  45.  
Success #stdin #stdout 0s 15240KB
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https://ideone.com/C1L4YW
language:
C++14 (gcc 8.3)
created:
7 years ago
visibility:
secret

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