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  1. #include <iostream>
  2. using namespace std;
  3.  
  4. struct MultiCallToken
  5. {
  6. private:
  7. 	bool inUse = false;
  8.  
  9. 	friend class MultiCallGuard;
  10. };
  11.  
  12. // guards against multiple calls
  13. class MultiCallGuard
  14. {
  15. public:
  16. 	~MultiCallGuard()
  17. 	{
  18. 		if(token && free)
  19. 		{
  20. 			token->inUse = false;
  21. 		}
  22. 	}
  23.  
  24. 	operator bool()
  25. 	{
  26. 		if(token->inUse)
  27. 			return false;
  28.  
  29. 		return token->inUse = free = true;
  30. 	}
  31.  
  32. 	MultiCallGuard(const MultiCallGuard&) = delete;
  33. 	MultiCallGuard& operator=(const MultiCallGuard&) = delete;
  34. 	MultiCallGuard(MultiCallGuard&& g) : token(g.token), free(g.free)
  35. 	{
  36. 		g.token = nullptr;
  37. 	}
  38.  
  39. 	MultiCallGuard& operator=(MultiCallGuard&& g)
  40. 	{
  41. 		token = g.token;
  42. 		free = g.free;
  43. 		g.token = nullptr;
  44. 	}
  45.  
  46. private:
  47. 	MultiCallGuard(MultiCallToken& token) : token(&token), free(false) {}
  48.  
  49. 	MultiCallToken* token;
  50. 	bool free;
  51.  
  52. 	friend MultiCallGuard guard(MultiCallToken&);
  53. };
  54.  
  55. MultiCallGuard guard(MultiCallToken& t)
  56. {
  57. 	MultiCallGuard g(t);
  58. 	return g;
  59. }
  60.  
  61. MultiCallToken fooToken;
  62. MultiCallToken barToken;
  63.  
  64. void bar();
  65.  
  66. void foo()
  67. {
  68. 	if(auto g = guard(fooToken))
  69. 	{
  70. 		cout << "foo called\n";
  71.  
  72. 		bar();
  73. 	}
  74. }
  75.  
  76. void bar()
  77. {
  78. 	if(auto g = guard(barToken))
  79. 	{
  80. 		cout << "bar called\n";
  81.  
  82. 		foo();
  83. 	}
  84. }
  85.  
  86. int main()
  87. {
  88. 	cout << ">> explicit call to foo:\n";
  89.  
  90. 	foo();
  91.  
  92. 	cout << "\n>> explicit call to bar\n";
  93.  
  94. 	bar();
  95.  
  96. 	return 0;
  97. }
Success #stdin #stdout 0s 3456KB
comments (?)
stdin
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Standard input is empty
stdout
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>> explicit call to foo:
foo called
bar called

>> explicit call to bar
bar called
foo called
https://ideone.com/MEBxar
language:
C++14 (gcc 8.3)
created:
8 years ago
visibility:
public

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