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  1. #include <cassert>
  2. #include <iostream>
  3.  
  4. template<typename T, typename R=void>
  5. struct ExtMethod {
  6.     ExtMethod& operator - () {
  7.         return *this;
  8.     }
  9.  
  10.     template<typename U>
  11.     R operator()( U& obj ) {
  12.         return static_cast<T*>(this)->operator()( obj );
  13.     }
  14. };
  15.  
  16. template<typename Derived>
  17. struct Extendible
  18. {
  19.     template<typename T, typename ReturnT>
  20.     ReturnT operator < ( ExtMethod<T, ReturnT>& extMethod ) {
  21.         return extMethod( static_cast<Derived&>( *this ) );
  22.     }
  23. };
  24.  
  25. struct Widget : Extendible<Widget> {
  26.     Widget( int size, int weight ) : size( size ), weight( weight ) {}
  27.  
  28.     int size;
  29.     int weight;
  30. };
  31. struct print : ExtMethod<print> {
  32.     void operator()( Widget& w ) {
  33.         std::cout << "size: " << w.size << ", weight: " << w.weight << std::endl;
  34.     }
  35. };
  36. struct density : ExtMethod<density, float> {
  37.     float operator()( Widget& w ) {
  38.        return (float)(w.weight / w.size);
  39.     }
  40. };
  41.  
  42. int main() {
  43.  
  44.     Widget w( 4, 10 );
  45.     w<-print();
  46.  
  47.     float d = w<-density();
  48.     assert( d - 10/4 < 0.01 );
  49. }
Success #stdin #stdout 0s 2852KB
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size: 4, weight: 10
https://ideone.com/jWHxu2
language:
C++ (gcc 8.3)
created:
11 years ago
visibility:
public

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