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  1. #include <iostream>
  2. #include <type_traits>
  3. #include <cstddef>
  4. #include <cstdint>
  5. #include <utility>
  6.  
  7. template <typename Type>
  8. struct LinkExtension;
  9.  
  10. template <typename Type>
  11. struct TypeEx {
  12. 	using Extension = typename LinkExtension<Type>::Type;
  13.  
  14. 	alignas(Type) uint8_t objectData[sizeof(Type)];
  15. 	alignas(Extension) uint8_t extensionData[sizeof(Extension)];
  16.  
  17. 	Type* getObject() { return reinterpret_cast<Type*>(objectData); }
  18. 	const Type* getObject() const { return reinterpret_cast<const Type*>(objectData); }
  19. 	Extension* getExtension() { return reinterpret_cast<Extension*>(extensionData); }
  20. 	const Extension* getExtension() const { return reinterpret_cast<const Extension*>(extensionData); }
  21.  
  22.     template <class... Args>
  23.     TypeEx(Args&&... args) 
  24.     {
  25.     	new (objectData) Type(std::forward<Args>(args)...);
  26.     	new (extensionData) Extension();
  27.     }
  28.     ~TypeEx() 
  29.     {
  30.     	getObject()->~Type();
  31.     	getExtension()->~Extension();
  32.     }
  33.     TypeEx(const TypeEx&) = delete;
  34.     TypeEx& operator = (const TypeEx&) = delete;
  35. };
  36.  
  37. template <typename Type, class... Args>
  38. Type* createObjectEx(Args&&... args)
  39. {
  40.    TypeEx<Type>* retVal = new TypeEx<Type>(std::forward<Args>(args)...);
  41.    return retVal->getObject();
  42. }
  43.  
  44. template <typename Type>
  45. typename LinkExtension<Type>::Type& getObjectEx(Type* obj)
  46. {
  47.    static_assert(std::is_standard_layout<TypeEx<Type>>::value, "Oops");
  48.    static_assert(offsetof(TypeEx<Type>, objectData) == 0, "Oops");
  49.    TypeEx<Type>* retVal = static_cast<TypeEx<Type>*>((void*)obj);
  50.     return *(retVal->getExtension());
  51. }
  52.  
  53. template <typename Type>
  54. const typename LinkExtension<Type>::Type& getObjectEx(const Type* obj)
  55. {
  56.     static_assert(std::is_standard_layout<TypeEx<Type>>::value, "Oops");
  57.     static_assert(offsetof(TypeEx<Type>, objectData) == 0, "Oops");
  58.     const TypeEx<Type>* retVal = static_cast<const TypeEx<Type>*>((const void*)obj);
  59.     return *(retVal->getExtension());
  60. }
  61.  
  62. template <typename Type>
  63. void deleteObjectEx(const Type* obj)
  64. {
  65.     const TypeEx<Type>* objectEx = static_cast<const TypeEx<Type>*>((const void*)obj);
  66.     delete objectEx;
  67. }
  68.  
  69.  
  70. class MyClass {
  71. public:
  72. 	virtual ~MyClass() = default;
  73. };
  74. struct MyClassExtension {
  75.     int a;
  76.     int b;
  77. };
  78. template <>
  79. struct LinkExtension<MyClass> {
  80.     typedef MyClassExtension Type;  
  81. };
  82.  
  83. void printExtension(MyClass* object);
  84. int main() {
  85.     MyClass* object = createObjectEx<MyClass>();
  86.     MyClassExtension& extension = getObjectEx(object);
  87.     extension.a = 1;
  88.     extension.b = 2;
  89.     printExtension(object);
  90.     deleteObjectEx(object);
  91.  
  92.     TypeEx<MyClass> objectEx;
  93.     objectEx.getExtension()->a = 3;
  94.     objectEx.getExtension()->b = 4;
  95.     printExtension(objectEx.getObject());
  96. }
  97.  
  98. void printExtension(MyClass* object)
  99. {
  100.     MyClassExtension& extension = getObjectEx(object);
  101.     std::cout << extension.a << ' ' << extension.b << std::endl;
  102. }
  103.  
Success #stdin #stdout 0s 16064KB
comments ()
stdin 
Standard input is empty
stdout 
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https://ideone.com/mmfK83
language:
C++14 (gcc 8.3)
created:
7 years ago
visibility:
public

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