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  1. #include <iostream>
  2. #include <string>
  3. using namespace std;
  4.  
  5. #include <boost/variant.hpp>
  6.  
  7. class Value {
  8. 	int x;
  9. public:
  10. 	explicit Value(int x) : x(x) {}
  11. 	Value(Value&&) = default;
  12. 	Value(const Value&) = delete;
  13. 	~Value() { x = 100500; }
  14.  
  15. 	int peek() const { return x; }
  16. };
  17.  
  18. Value fa() {
  19. 	Value a(1);
  20. 	return a;
  21. }
  22. Value ga() {
  23. 	Value a(1);
  24. 	Value& ra = a;
  25. 	return move(ra);
  26. }
  27. auto ha() {
  28. 	Value a(1);
  29. 	return [aa(move(a))]() mutable -> Value { return move(aa); };
  30. }
  31.  
  32. using Either = boost::variant<Value, string>;
  33.  
  34. Either&& emove(Either& e) { return static_cast<Either&&>(e); }
  35.  
  36. Either fe() {
  37. 	Either a("aaa");
  38. 	return a;
  39. }
  40. Either ge() {
  41. 	Either a(Value(123));
  42. 	Either& ra = a;
  43. 	// cannot explicitly move, had to trick with static-cast
  44. 	// return move(ra);
  45. 	return emove(ra);
  46. }
  47. auto he() {
  48. 	Either a(Value(456));
  49. 	cout << "he : " << &a << endl;
  50. 	// cannot bind to moved
  51. 	// return [=]() mutable -> Either { return a; };
  52. 	// return [a(move(a))]() mutable -> Either { return move(a); }
  53. 	return [&a, aa(emove(a))]() mutable -> Either {
  54. 		cout << "ll : " << &aa << " != " << &a << endl;
  55. 		return emove(aa);
  56. 	};
  57. }
  58.  
  59. Value peek(Either&& e) {
  60. 	return boost::get<Value>(emove(e));
  61. }
  62. Value peekpeek(Either e) {
  63. 	return peek(emove(e));
  64. }
  65.  
  66.  
  67. int main() {
  68. 	cout << boost::get<Value>(ge()).peek() << endl;
  69. 	cout << boost::get<Value>(he()()).peek() << endl;
  70. }
Success #stdin #stdout 0s 4504KB
comments (?)
stdin 
Standard input is empty
stdout 
123
he : 0x7ffdf9defad0
ll : 0x7ffdf9defb78 != 0x7ffdf9defad0
456
https://ideone.com/uF57MI
damned boost::variant with move semantics
language:
C++14 (gcc 8.3)
created:
4 years ago
visibility:
public

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