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  1. #include <iostream>
  2. #include <array>
  3. #include <limits>
  4. #include <string>
  5. #include <tuple>
  6. #include <vector>
  7. #include <functional>
  8.  
  9.         template<class Tx, class ... Tr> class VariantIndex;
  10.  
  11.                 template<class Tx> class VariantIndex<Tx>
  12.                 {
  13.                 public:
  14.                 private:
  15.                 };
  16.  
  17.                 template<class Tx, class ... Tr> class VariantIndex<Tx, Tx, Tr ...>
  18.                 {
  19.                 public:
  20.                         static constexpr std::size_t index = 1;
  21.                 private:
  22.                 };
  23.  
  24.                 template<class Tx, class Ty, class ... Tr> class VariantIndex<Tx, Ty, Tr ...>
  25.                 {
  26.                 public:
  27.                         static constexpr std::size_t index = VariantIndex<Tx, Tr ...>::index + 1;
  28.                 private:
  29.                 };
  30.  
  31.                 template<class ... Tl>
  32.                 class Variant
  33.                 {
  34.                 public:
  35.                         Variant()
  36.                         : m_Type(0)
  37.                         , m_Deleter(nullptr)
  38.                         , m_Data(nullptr)
  39.                         {
  40.                         }
  41.  
  42.                         ~Variant()
  43.                         {
  44.                                 if(m_Type && m_Deleter && m_Data)
  45.                                 {
  46.                                         m_Deleter(m_Data);
  47.                                 }
  48.                                 else
  49.                                 {
  50.                                         if(m_Type || m_Deleter || m_Data)
  51.                                         {
  52.                                                 //LOG << "Type, deleter and data must be set together.";
  53.                                         }
  54.                                 }
  55.                         }
  56.  
  57.     		template<class T> static Variant MakeByType(const T& t)
  58.                         {
  59.                                 return Make<VariantIndex<T, Tl ...>::index, T>(t);
  60.                         }
  61.                         std::size_t m_Type; ///< Index of type.
  62.                         std::function<void(void*)> m_Deleter; ///< 
  63.                         void *m_Data; ///< Pointer to data.
  64.  
  65. 			template<class T> bool IsType() const
  66. 			{
  67. 				return m_Type == VariantIndex<T, Tl ...>::index;
  68. 			}
  69.  
  70. 			template<class T> const T& GetType() const
  71. 			{
  72. 				return *reinterpret_cast<const T*>(m_Data);
  73. 			}
  74.                 private:
  75. 			template<std::size_t I, class T> static Variant Make(const T& t)
  76.                         {
  77.                                 return Variant(I, [](void *ptr){ std::cout << "Delete type " << I << std::endl; delete reinterpret_cast<T*>(ptr); }, new T(t));
  78.                         }
  79.                         Variant(std::size_t type, std::function<void(void*)>&& deleter, void *data)
  80.                         : m_Type(type)
  81.                         , m_Deleter(std::move(deleter))
  82.                         , m_Data(data)
  83.                         {
  84.                         }
  85.                 };
  86.  
  87.  
  88. typedef Variant<int, std::string, char> TestVar;
  89.  
  90. int main(int,char**)
  91. {
  92.     TestVar v = TestVar::MakeByType<int>('a');
  93.     std::cout << v.m_Type << std::endl;
  94.     if(v.IsType<int>())
  95.     {
  96.     	std::cout << "int: " << v.GetType<int>() << std::endl;
  97.     }
  98.     return 0;
  99. }
Success #stdin #stdout 0s 2988KB
comments (?)
stdin 
Standard input is empty
stdout 
1
int: 97
Delete type 1
https://ideone.com/Itoky6
language:
C++14 (gcc 8.3)
created:
11 years ago
visibility:
public

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