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  1. #include <exception>
  2. #include <utility>
  3. #include <type_traits>
  4.  
  5. template<typename F, typename CleanupPolicy>
  6. class scope_guard : CleanupPolicy, CleanupPolicy::installer
  7. {
  8.     using CleanupPolicy::cleanup;
  9.     using CleanupPolicy::installer::install;
  10.  
  11.     typename std::remove_reference<F>::type f_;
  12.  
  13. public:
  14.     scope_guard(F&& f) : f_(std::forward<F>(f)) { 
  15.         install();
  16.     }
  17.     ~scope_guard() {
  18.     	cleanup(f_);
  19. 	}
  20. };
  21.  
  22. struct unchecked_install_policy {
  23. 	void install() { }
  24. };
  25.  
  26. struct checked_install_policy {
  27. 	void install() {
  28. 		if (std::uncaught_exception()) {
  29. 			std::terminate(); // sorry
  30. 		}
  31. 	}
  32. };
  33.  
  34. struct exit_policy {
  35. 	typedef unchecked_install_policy installer;
  36.  
  37.     template<typename F>
  38.     void cleanup(F& f) {
  39.         f();
  40.     }
  41. };
  42.  
  43. struct failure_policy {
  44. 	typedef checked_install_policy installer;
  45.  
  46.     template<typename F>
  47.     void cleanup(F& f) {
  48.         // Only cleanup if we're exiting from an exception.
  49.         if (std::uncaught_exception()) {
  50.             f();
  51.         }
  52.     }
  53. };
  54.  
  55. struct success_policy {
  56. 	typedef checked_install_policy installer;
  57.  
  58.     template<typename F>
  59.     void cleanup(F& f) {
  60.         // Only cleanup if we're NOT exiting from an exception.
  61.         if (!std::uncaught_exception()) {
  62.            f();
  63.         }
  64.     }
  65. };
  66.  
  67. //////////////////////////////////////////////
  68. // Syntactical sugar
  69. //////////////////////////////////////////////
  70.  
  71. template<typename CleanupPolicy>
  72. struct scope_guard_builder { };
  73.  
  74. template<typename F, typename CleanupPolicy>
  75. scope_guard<F,CleanupPolicy> 
  76. operator+(
  77. 	scope_guard_builder<CleanupPolicy> builder,
  78. 	F&& f
  79. 	)
  80. {
  81. 	return std::forward<F>(f);
  82. }
  83.  
  84. // typical preprocessor utility stuff.
  85. #define PASTE_TOKENS2(a,b) a ## b
  86. #define PASTE_TOKENS(a,b) PASTE_TOKENS2(a,b)
  87.  
  88. #define scope(condition) \
  89.     auto PASTE_TOKENS(_scopeGuard, __LINE__) = \
  90.         scope_guard_builder<condition##_policy>() + [&]
  91.  
  92. //////////////////////////////////////////////
  93. // User code from here on
  94. //////////////////////////////////////////////
  95.  
  96. #include <iostream>
  97.  
  98. struct HasScopeExitInDtor {
  99. 	~HasScopeExitInDtor() {
  100. 		scope (exit) {
  101. 			std::cout << "scope (exit) in dtor success test\n";
  102. 		};
  103. 		try {
  104. 			std::cout << "scope (exit) in dtor failure test\n";
  105. 			throw 1;
  106. 		} catch (...) { }
  107. 	}
  108. };
  109.  
  110. struct HasScopeSuccessInDtor {
  111. 	~HasScopeSuccessInDtor() {
  112. 		std::cout << std::flush;
  113. 		scope (success) {
  114. 			std::cout << "error: scope (success) used in dtor\n";
  115. 		};
  116. 	}
  117. };
  118.  
  119. int main()
  120. {
  121. 	{
  122. 		const char* captureTest = nullptr;
  123. 		scope (exit) {
  124. 			std::cout << "scope (exit) success test\n";
  125. 			std::cout << "captureTest: " << captureTest;
  126. 		};
  127. 		scope (success) {
  128. 			std::cout << "scope (success) success test\n";
  129. 		};
  130. 		scope (failure) {
  131. 			std::cout << "scope (failure) success test\n";
  132. 		};
  133. 		captureTest = "ok\n";
  134. 	}
  135. 	try {
  136. 		HasScopeSuccessInDtor s;
  137.  
  138. 		scope (exit) {
  139. 			std::cout << "scope (exit) failure test\n";
  140. 		};
  141. 		scope (success) {
  142. 			std::cout << "scope (success) failure test\n";
  143. 		};
  144. 		scope (failure) {
  145. 			std::cout << "scope (failure) failure test\n";
  146. 		};
  147.  
  148. 		HasScopeExitInDtor e;
  149.  
  150. 		throw 1;
  151. 	} catch (...) {	}
  152. }
Runtime error #stdin #stdout #stderr 0s 3428KB
comments (?)
stdin
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Standard input is empty
stdout
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scope (success) success test
scope (exit) success test
captureTest: ok
scope (exit) in dtor failure test
scope (exit) in dtor success test
scope (failure) failure test
scope (exit) failure test
stderr
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terminate called without an active exception
https://ideone.com/2IpHBG
language:
C++14 (gcc 8.3)
created:
10 years ago
visibility:
public

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