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  1. #include <iostream>
  2. #include <sstream>
  3.  
  4. struct Statement;
  5. struct Logger;
  6. struct ComponentBase;
  7.  
  8. //------------------------------------------------------------------------------
  9.  
  10. struct ComponentBase {
  11. 	mutable ComponentBase *next;
  12. 	ComponentBase() : next(nullptr) { }
  13. 	virtual std::string toString() = 0;
  14. };
  15.  
  16. template <typename T>
  17. struct Component : ComponentBase {
  18. 	T value;
  19. 	Component(T value) : value(value) { }
  20. 	~Component() { }
  21. 	virtual std::string toString() {
  22. 		std::stringstream ss;
  23. 		ss << value;
  24. 		return ss.str();
  25. 	}
  26. };
  27.  
  28. struct ComponentIterator {
  29. 	ComponentBase *ptr;
  30. 	ComponentIterator(ComponentBase *ptr) : ptr(ptr) { }
  31. 	ComponentBase &operator*() { return *ptr; }
  32. 	void operator++() { ptr = ptr->next; }
  33. 	bool operator!=(ComponentIterator &other) { return (ptr != other.ptr); }
  34. };
  35.  
  36. //------------------------------------------------------------------------------
  37.  
  38. struct Statement {
  39. 	Logger *logger;
  40. 	ComponentBase *front;
  41. 	ComponentBase *back;
  42. 	ComponentIterator begin() { return front; }
  43. 	ComponentIterator end() { return nullptr; }
  44.  
  45. 	template <typename T>
  46. 	Statement(Logger &logger, Component<T> &component)
  47. 	: logger(&logger), front(&component), back(&component) { }
  48. 	~Statement();
  49.  
  50. 	template <typename T>
  51. 	Statement &operator<<(Component<T> &&component) {
  52. 		back->next = &component;
  53. 		back = &component;
  54. 		return *this;
  55. 	}
  56. };
  57.  
  58. //------------------------------------------------------------------------------
  59.  
  60. struct Logger {
  61. 	template <typename T>
  62. 	Statement operator<<(Component<T> &&component) {
  63. 		return {*this, component};
  64. 	}
  65.  
  66. 	virtual void log(Statement &statement) = 0;
  67. };
  68.  
  69. Statement::~Statement() {
  70. 	logger->log(*this);
  71. }
  72.  
  73. //------------------------------------------------------------------------------
  74.  
  75. template <typename T>
  76. Component<T const &> wrap(T const &value) {
  77. 	return value;
  78. }
  79. template <size_t N>
  80. Component<char const *> wrap(char const (&value)[N]) {
  81. 	return value;
  82. }
  83.  
  84. //------------------------------------------------------------------------------
  85.  
  86. struct MyLogger : public Logger {
  87. 	virtual void log(Statement &statement) override {
  88. 		for(auto &&component : statement) {
  89. 			std::cout << component.toString();
  90. 		}
  91. 		std::cout << std::endl;
  92. 	}
  93. };
  94.  
  95. int main() {
  96. 	std::string variable = "string";
  97. 	MyLogger logger;
  98. 	logger << wrap("Option ") << wrap(variable) << wrap(" is ") << wrap(42);
  99. }
  100.  
Success #stdin #stdout 0s 3464KB
comments (?)
stdin 
Standard input is empty
stdout 
Option string is 42
https://ideone.com/dom6vU
language:
C++14 (gcc 8.3)
created:
10 years ago
visibility:
public

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