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  1. #include <iostream>
  2. #include <memory>
  3.  
  4. class any_ptr
  5. {
  6.     struct WrapperBase
  7.     {
  8.     	virtual ~WrapperBase(){}
  9.     };
  10.  
  11.     template<typename T>
  12.     struct Wrapper : WrapperBase, T
  13.     {
  14. 		template<typename ... Args>
  15.     	Wrapper( Args&&... args ):
  16.     		T( std::forward<Args>(args)... ) {}
  17.     };
  18.  
  19.     std::unique_ptr<WrapperBase> mPtr;
  20.  
  21. 	any_ptr( std::unique_ptr<WrapperBase> ptr ):
  22. 		mPtr{ std::move(ptr) } {}
  23.  
  24. public:
  25.  
  26. 	template< typename T >
  27. 	explicit operator T*()
  28. 	{
  29. 		return dynamic_cast<T*>(mPtr.get());
  30. 	}
  31.  
  32. 	template< typename T >
  33. 	explicit operator T const*() const
  34. 	{
  35. 		return dynamic_cast<T*>(mPtr.get());
  36. 	}
  37.  
  38. 	template<typename T>
  39. 	friend any_ptr make_any_ptr( T&& t )
  40. 	{
  41. 		return std::unique_ptr<WrapperBase>{ new Wrapper<T>{ std::forward<T>(t) } };
  42. 	}
  43.  
  44. 	template< typename T,
  45. 	          typename ... Args >
  46. 	friend any_ptr make_any_ptr( Args&&... args )
  47. 	{
  48. 		return std::unique_ptr<WrapperBase>{ new Wrapper<T>{ std::forward<Args>(args)... } };
  49. 	}
  50. };
  51.  
  52. ////////////////////////////////////////////////////////////////////////////////
  53.  
  54. template <class T>
  55. bool inspect(any_ptr& p, void (&fun)(T))
  56. {
  57. 	using actual_t = typename std::remove_reference<T>::type;
  58.  
  59. 	if( actual_t* t = static_cast<actual_t*>(p) )
  60. 		fun(*t);
  61.  
  62. 	return false;
  63. }
  64.  
  65. ////////////////////////////////////////////////////////////////////////////////
  66.  
  67. class printable
  68. {
  69. public:
  70. 	virtual void print() const = 0;
  71. };
  72.  
  73. ////////////////////////////////////////////////////////////////////////////////
  74.  
  75. #include <string>
  76. using namespace std;
  77.  
  78. class foo : public printable
  79. {
  80. public:
  81. 	foo(string const& s) : m_s(s) {}
  82.  
  83. 	virtual void print() const
  84. 	{
  85. 		cout << "foo: " << m_s << "\n";
  86. 	}
  87.  
  88. private:
  89. 	string m_s;
  90. };
  91.  
  92. class bar : public printable
  93. {
  94. public:
  95. 	bar(int i) : m_i(i) {}
  96.  
  97. 	virtual void print() const
  98. 	{
  99. 		cout << "bar: " << m_i << "\n";
  100. 	}
  101.  
  102. private:
  103. 	int m_i;
  104. };
  105.  
  106. ////////////////////////////////////////////////////////////////////////////////
  107.  
  108. void print_printable(printable& p)
  109. {
  110. 	p.print();
  111. }
  112.  
  113. ////////////////////////////////////////////////////////////////////////////////
  114.  
  115. int main()
  116. {
  117. 	auto f = make_any_ptr(foo("foo"));
  118. 	auto b = make_any_ptr(bar(42));
  119.  
  120. 	inspect(f, print_printable);
  121. 	inspect(b, print_printable);
  122. }
Success #stdin #stdout 0s 3476KB
comments (?)
stdin 
Standard input is empty
stdout 
foo: foo
bar: 42
https://ideone.com/yMrCqb
language:
C++14 (gcc 8.3)
created:
12 years ago
visibility:
public

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