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  1. #include <utility>
  2. #include <iostream>
  3. #include <memory>
  4.  
  5.  
  6. template<class T>
  7. struct moved_value{
  8.     moved_value(T* v):pval(v){};
  9.  
  10. 	T& get(){return *pval;}
  11. 	const T& get()const{return *pval;}
  12.  
  13. private:
  14. 	T* pval;
  15.  
  16. };
  17. // Copied with removal of Parameter info from 
  18. // http://stackoverflow.com/questions/7943525/is-it-possible-to-figure-out-the-parameter-type-and-return-type-of-a-lambda
  19.  
  20.  
  21. template <typename T>
  22. struct function_traits
  23.     : public function_traits<decltype(&T::operator())>
  24. {};
  25. // For generic types, directly use the result of the signature of its 'operator()'
  26.  
  27. template <typename ClassType, typename ReturnType, typename... Args>
  28. struct function_traits<ReturnType(ClassType::*)(Args...) const>
  29. // we specialize for pointers to member function
  30. {
  31.     typedef ReturnType result_type;
  32.  
  33. };
  34.  
  35. template<class T,class F>
  36. struct move_lambda{
  37. 	T val;
  38. 	F f_;
  39.  
  40. 	typedef function_traits<F> traits;
  41. 	typedef typename traits::result_type result_type;
  42.  
  43.  
  44.  
  45. 	move_lambda(T&& v, F f):val(std::move(v)),f_(f){};
  46. 	move_lambda(move_lambda&& other):val(std::move(other.val)),f_(std::move(other.f_)){}
  47.  
  48. 	move_lambda& operator=(move_lambda&& other){
  49. 		val = std::move(other.val);
  50. 		f_ = std::move(other.f_);
  51.  
  52. 	}
  53.  
  54. 	template<class... Args>
  55. 	auto operator()(Args&& ...args) -> result_type
  56. 	{
  57. 	    moved_value<T> mv(&val);
  58. 		return f_(mv,std::forward<Args>(args)...);
  59.  
  60. 	}
  61.  
  62.  
  63.  
  64. private:
  65. 	move_lambda();
  66. 	move_lambda(const move_lambda&);
  67. 	move_lambda& operator=(const move_lambda&);
  68.  
  69.  
  70.  
  71.  
  72. };
  73.  
  74. template<class T,class F>
  75. move_lambda<T,F>create_move_lambda(T&& t, F f){
  76. 	return move_lambda<T,F>(std::move(t),f);
  77. }
  78.  
  79. // Unfortunately, std::function does not seem to support move-only callables
  80. // Here is our quick movable replacement
  81. template< class ReturnType, class... ParamTypes>
  82. struct movable_function_base{
  83. 	virtual ReturnType callFunc(ParamTypes&&... p) = 0;
  84.  
  85. };
  86.  
  87.  
  88. template<class F, class ReturnType, class... ParamTypes>
  89. struct movable_function_imp:public movable_function_base<ReturnType,ParamTypes...>{
  90. 		F f_;
  91. 	virtual ReturnType callFunc(ParamTypes&&... p){
  92. 		return f_(std::forward<ParamTypes>(p)...);
  93. 	}
  94.  
  95. 	explicit movable_function_imp(F&& f):f_(std::move(f)){};
  96.  
  97.  
  98.  
  99. private:
  100. 	movable_function_imp();
  101. 	movable_function_imp(const movable_function_imp&);
  102. 	movable_function_imp& operator=(const movable_function_imp&);
  103. };
  104.  
  105.  
  106. template<class FuncType>
  107. struct movable_function{};
  108.  
  109. template<class ReturnType, class... ParamTypes>
  110. struct movable_function<ReturnType(ParamTypes...)>{
  111. 	std::unique_ptr<movable_function_base<ReturnType,ParamTypes...>> ptr_;
  112.  
  113. 	template<class F>
  114. 	explicit movable_function(F&& f):ptr_(new movable_function_imp<F,ReturnType,ParamTypes...>(std::move(f))){}
  115. 	movable_function(movable_function&& other):ptr_(std::move(other.ptr_)){}
  116. 	movable_function& operator=(movable_function&& other){
  117. 		ptr_ = std::move(other.ptr_);
  118. 		return *this;
  119. 	}
  120.  
  121. 	template<class... Args>
  122. 	auto operator()(Args&& ...args) -> ReturnType
  123. 	{
  124. 	    return ptr_->callFunc(std::forward<Args>(args)...);
  125.  
  126. 	}
  127. private:
  128. 	movable_function();
  129. 	movable_function(const movable_function&);
  130. 	movable_function& operator=(const movable_function&);
  131.  
  132. };
  133.  
  134.  
  135.  
  136.  
  137. struct TestMove{
  138. 	TestMove():k(0){}
  139. 	TestMove(TestMove&& other):k(other.k){
  140. 		other.k = -1;
  141. 	}
  142. 	TestMove& operator=(TestMove&& other){
  143. 		k = other.k;
  144. 		other.k = -1;
  145. 		return *this;
  146. 	}
  147.  
  148. 	int k;
  149. private:
  150. 	TestMove(const TestMove&);
  151. 	TestMove& operator=(const TestMove&);
  152.  
  153.  
  154. };
  155.  
  156. movable_function<void()> CreateLambda()
  157.  
  158. {
  159.    typedef TestMove HugeObject;
  160.    HugeObject hugeObj;
  161.    hugeObj.k = 9;
  162.  
  163.     // ...preparation of hugeObj...
  164.  
  165.  
  166.    auto f = create_move_lambda(std::move(hugeObj),[](moved_value<HugeObject> hugeObj){// manipulate huge object
  167. 		std::cout << hugeObj.get().k << std::endl;
  168.  
  169.    });
  170.  
  171.   movable_function<void()> toReturn(std::move(f));
  172.  
  173.   return toReturn;
  174.  
  175. }
  176.  
  177.  
  178. int main(){
  179.  
  180. 	// A movable only type, not copyable
  181. 	TestMove m;
  182. 	m.k = 5;
  183.  
  184. 	// A movable only type, not copyable
  185. 	TestMove m2;
  186. 	m2.k = 6;
  187.  
  188. 	// Create a lambda that takes 2 parameters and returns int
  189. 	auto lambda = create_move_lambda(std::move(m),[](moved_value<TestMove> m,int i,int)->int{std::cout << m.get().k << " " << i << std::endl;return 7;});
  190.  
  191. 	// Create a lambda that takes 0 parameters and returns void
  192. 	auto lambda2 = create_move_lambda(std::move(m2),[](moved_value<TestMove> m){std::cout << m.get().k << std::endl;});
  193.  
  194.  
  195. 	std::cout <<  lambda(1,2) << std::endl;
  196.  
  197. 	lambda2();
  198.  
  199.  
  200.  
  201.  
  202. 	// Compiler error if you try to copy
  203. 	//auto lambda4 = lambda;
  204.  
  205. 	// Able to move
  206. 	auto lambda3 = std::move(lambda2);
  207. 	lambda3();
  208.  
  209. 	auto lambda4 = CreateLambda();
  210.  
  211. 	lambda4();
  212.  
  213. }
  214.  
Success #stdin #stdout 0s 3060KB
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https://ideone.com/OXYVyp
language:
C++14 (gcc 8.3)
created:
11 years ago
visibility:
secret

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