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  1. #include <iostream>
  2. using namespace std;
  3.  
  4.  
  5. template <typename T>
  6. struct St1
  7. {
  8.     St1 () = default;
  9.  
  10.     St1 (const St1& other) : hasValue (other.hasValue) { if (hasValue) value = other.value; }
  11.  
  12.     St1 (St1&& other) : hasValue (other.hasValue) { if (hasValue) value = std::move(other.value); }
  13.  
  14. 	template <typename Arg0, typename... Args >
  15.     explicit St1 (Arg0 arg0, Args&&... args) : hasValue (true) { value = T(std::forward<Arg0>(arg0), std::forward<Args>(args)...); }
  16.  
  17. 	T value;
  18. 	bool hasValue { false };
  19. };
  20.  
  21. template <typename T>
  22. struct St2
  23. {
  24.     St2 () = default;
  25.  
  26.     St2 (const St2& other) : hasValue (other.hasValue) { if (hasValue) value = other.value; }
  27.  
  28.     St2 (St2&& other) : hasValue (other.hasValue) { if (hasValue) value = std::move(other.value); }
  29.  
  30.     explicit St2 (const T &value) : hasValue (true) { this->hasValue = value; }
  31.  
  32.     explicit St2 (T &&value) : hasValue (true) { this->value = std::move(value); }
  33.  
  34. 	T value;
  35. 	bool hasValue { false };
  36. };
  37.  
  38. template <typename T>
  39. struct St3
  40. {
  41.     St3 () = default;
  42.  
  43.     St3 (const St3& other) : hasValue (other.hasValue) { if (hasValue) value = other.value; }
  44.  
  45.     St3 (St3&& other) : hasValue (other.hasValue) { if (hasValue) value = std::move(other.value); }
  46.  
  47. 	template <typename... Args >
  48.     explicit St3 (Args&&... args) : hasValue (true) { value = T(std::forward<Args>(args)...); }
  49.  
  50. 	T value;
  51. 	bool hasValue { false };
  52. };
  53.  
  54. template <typename T>
  55. struct St4
  56. {
  57.     St4 () = default;
  58.  
  59.     St4 (const St4& other) : hasValue (other.hasValue) { if (hasValue) value = other.value; }
  60.  
  61.     St4 (St4&& other) : hasValue (other.hasValue) { if (hasValue) value = std::move(other.value); }
  62.  
  63. 	explicit St4 (T value) : hasValue (true) { this->value = value; }
  64.  
  65. 	template <typename... Args >
  66.     explicit St4 (Args&&... args) : hasValue (true) { value = T(std::forward<Args>(args)...); }
  67.  
  68. 	T value;
  69. 	bool hasValue { false };
  70. };
  71.  
  72. template <typename T>
  73. struct St5
  74. {
  75. 	St5 () {};
  76.  
  77.     St5 (const St5& other) : hasValue (other.hasValue) { if (hasValue) value = other.value; }
  78.  
  79.     St5 (St5&& other) : hasValue (other.hasValue) { if (hasValue) value = std::move(other.value); }
  80.  
  81. 	explicit St5 (T value) : hasValue (true) { this->value = value; }
  82.  
  83. 	template <typename... Args >
  84.     explicit St5 (Args&&... args) : hasValue (true) { value = T(std::forward<Args>(args)...); }
  85.  
  86. 	T value;
  87. 	bool hasValue { false };
  88. };
  89.  
  90.  
  91. int main() {
  92.  
  93. 	St1<int> a1;
  94. 	St1<int> a2 {2};
  95. 	St1<int> a3 {};
  96.  
  97. 	St2<int> b1;
  98. 	St2<int> b2 {2};
  99. 	St2<int> b3 {};
  100.  
  101. 	St3<int> c1;
  102. 	St3<int> c2 {2};
  103. 	St3<int> c3 {};
  104.  
  105. 	St4<int> d1;
  106. 	St4<int> d2 {2};
  107. 	St4<int> d3 {};
  108.  
  109. 	St5<int> e1;
  110. 	St5<int> e2 {2};
  111. 	St5<int> e3 {};
  112.  
  113. 	cout << "St1:\n";
  114. 	cout << (a1.hasValue == 0) << '\n';
  115. 	cout << (a2.hasValue == 1) << '\n';
  116. 	cout << (a2.value == 2) << '\n';
  117. 	cout << (a3.hasValue == 0) << '\n';
  118.  
  119. 	cout << "St2:\n";
  120. 	cout << (b1.hasValue == 0) << '\n';
  121. 	cout << (b2.hasValue == 1) << '\n';
  122. 	cout << (b2.value == 2) << '\n';
  123. 	cout << (b3.hasValue == 0) << '\n';
  124.  
  125. 	cout << "St3:\n";
  126. 	cout << (c1.hasValue == 0) << '\n';	// failed in VS
  127. 	cout << (c2.hasValue == 1) << '\n';	// failed in VS
  128. 	cout << (c2.value == 2) << '\n';	// failed in VS
  129. 	cout << (c3.hasValue == 0) << '\n';
  130.  
  131. 	cout << "St4:\n";
  132. 	cout << (d1.hasValue == 0) << '\n';	// failed in VS
  133. 	cout << (d2.hasValue == 1) << '\n';
  134. 	cout << (d2.value == 2) << '\n';
  135. 	cout << (d3.hasValue == 0) << '\n';
  136.  
  137. 	cout << "St5:\n";
  138. 	cout << (e1.hasValue == 0) << '\n';
  139. 	cout << (e2.hasValue == 1) << '\n';
  140. 	cout << (e2.value == 2) << '\n';
  141. 	cout << (e3.hasValue == 0) << '\n';
  142.  
  143. 	return 0;
  144. }
Success #stdin #stdout 0s 16064KB
comments (?)
stdin
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Standard input is empty
stdout
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St1:
1
1
1
1
St2:
1
1
1
1
St3:
1
1
1
1
St4:
1
1
1
1
St5:
1
1
1
1
https://ideone.com/rPkhd5
language:
C++14 (gcc 8.3)
created:
6 years ago
visibility:
public

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