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  1. #include <iostream>
  2. #include <sstream>
  3. #include <vector>
  4. #include <algorithm>
  5. #include <functional>
  6.  
  7. template <class T, class U>
  8. class Conversion {
  9. public:
  10.     Conversion(const std::function<U(const T&)>& f) : f(f) {}
  11.     U convert (const T& v) const { return f(v); }
  12. private:
  13.    std::function<U(const T&)>  f;
  14. };
  15. template <class T>
  16. class Conversion<T,T> {
  17. public:
  18.     T convert (const T& v) const { return v; }
  19. };
  20.  
  21.  
  22. template <class T>
  23. class ConvertFunctions0 : public Conversion<T,T> {};
  24.  
  25. template <class T, class V1>
  26. class ConvertFunctions1 : public Conversion<T,T>, public Conversion<T,V1> {
  27. public:
  28.   ConvertFunctions1(std::function<V1(const T&)> f1) : Conversion<T,V1>(f1) {}
  29. };
  30.  
  31. template <class T, class V1, class V2>
  32. class ConvertFunctions2 : public Conversion<T,T>, public Conversion<T,V1>, public Conversion<T,V2> {
  33. public:
  34.   ConvertFunctions2(std::function<V1(const T&)> f1, std::function<V2(const T&)> f2) 
  35.   : Conversion<T,V1>(f1), Conversion<T,V2>(f2) 
  36.   {}
  37. };
  38.  
  39. template <class T, class CF>
  40. class MultiUnitValue {
  41. public:
  42.    MultiUnitValue(T v, const CF& cf) : v(v), cf(cf) {}
  43.  
  44.    template <class U>
  45.    U in() const
  46.    {
  47.       return cf.Conversion<T,U>::convert(v);
  48.    }
  49.  
  50. private:
  51.    T v;
  52.    CF cf;
  53. };
  54.  
  55. int main(){
  56.   auto f1 = [](int i){return i*2.54;};
  57.   auto f2 = [](int i){ std::stringstream ss; ss << i; return ss.str(); };
  58.   typedef ConvertFunctions2<int, float, std::string> CF_f1_f2;
  59.   MultiUnitValue<int, CF_f1_f2>  vv(1, CF_f1_f2(f1, f2));
  60.   std::cout << vv.in<int>() << "\n";
  61.   std::cout << vv.in<float>() << "\n";
  62.   std::cout << vv.in<std::string>() << "\n";
  63.   // std::cout << vv.in<long>() << "\n"; // error to compile
  64. }
Success #stdin #stdout 0s 3024KB
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2.54
1
https://ideone.com/qhsDSR
language:
C++14 (gcc 8.3)
created:
11 years ago
visibility:
public

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