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  1. #include <algorithm>
  2. #include <iostream>
  3.  
  4. template <typename T>
  5. struct A {
  6.  
  7. 	A(std::size_t size) 
  8. 	: size_(size), 
  9. 	  t_(new T[size]) { 
  10. 	}
  11.  
  12. 	~A() {
  13. 		delete[] t_;
  14. 	}
  15.  
  16. 	A(const A &a) {
  17. 		t_ = new T[a.size_];
  18. 		std::copy(a.t_, a.t_ + a.size_, t_);
  19. 	}
  20.  
  21. 	A(A &&a) {
  22. 		t_ = a.t_;
  23. 		size_ = a.size_;
  24.  
  25. 		a.t_ = 0; 
  26. 	}
  27.  
  28. 	A& operator = (A a) {
  29. 		//  unified assignment operator, only need one assignment operator
  30. 		//  If the value is passed as rvalue, the move ctor will be invoked
  31. 		//  If the value is passed as lvalue, the copy ctor will be invoked
  32. 		swap(*this, a);
  33. 		return *this;
  34. 	}
  35.  
  36. 	T& operator [](size_t element) {
  37. 		return t_[element];
  38. 	}
  39.  
  40. 	const T& operator[](size_t element) const {
  41. 		return t_[element];
  42. 	}
  43.  
  44. 	size_t size() {
  45. 		return size_;
  46. 	}
  47.  
  48. private:
  49.  
  50. 	friend void swap(A &first, A &second) {
  51. 		//  custom swap function, used to reduce code duplication		
  52. 		std::swap(first.t_,second.t_);
  53. 		std::swap(first.size_, second.size_);
  54. 	}
  55.  
  56. 	T *t_; 
  57. 	std::size_t size_;
  58. };
  59.  
  60. template <typename T>
  61. struct B {
  62.  
  63. 	B(A<T> a1, A<T> a2) 
  64. 	: a1_(a1), 
  65. 	  a2_(a2) {
  66.  
  67. 	}
  68.  
  69. 	B(const B& b) 
  70. 	: a1_(b.a1_),
  71. 	  a2_(b.a2_) {
  72.  
  73. 	}
  74.  
  75. 	B(B && b) 
  76. 	: a1_(std::move(b.a1_)),
  77. 	  a2_(std::move(b.a2_)) {
  78.  
  79. 	}
  80.  
  81. 	B& operator = (B b) {
  82. 		//  unified assignment operator, only need one assignment operator
  83. 		//  If the value is passed as rvalue, the move ctor will be invoked
  84. 		//  If the value is passed as lvalue, the copy ctor will be invoked
  85. 		swap(*this, b);
  86. 		return *this;
  87. 	}
  88.  
  89. private:
  90.  
  91. 	friend void swap(B &first, B& second) {
  92. 		std::swap(first.a1_, second.a1_);
  93. 		std::swap(first.a2_, second.a2_);
  94. 	}
  95.  
  96. 	A<T> a1_;
  97. 	A<T> a2_;
  98.  
  99. };
  100.  
  101. int main() {
  102.     A<int> c(3);
  103.     B<int> d(c, c);
  104.     swap(d, c);
  105. }
Compilation error #stdin compilation error #stdout 0s 0KB
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stdin
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Standard input is empty
compilation info 
prog.cpp: In function 'int main()':
prog.cpp:104:14: error: no matching function for call to 'swap(B<int>&, A<int>&)'
prog.cpp:91:14: note: candidates are: void swap(B<int>&, B<int>&)
prog.cpp:50:14: note:                 void swap(A<int>&, A<int>&)
stdout
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Standard output is empty
https://ideone.com/tIUYy
language:
C++14 (gcc 8.3)
created:
13 years ago
visibility:
secret

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