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  1. #include <iostream>
  2. #include <vector>
  3. #include <initializer_list>
  4.  
  5. struct Test {
  6. 	std::string pString;
  7. 	Test(){
  8. 		std::cout << "construct" << std::endl;
  9. 	}
  10. 	Test(const std::string& aString):pString(aString){
  11. 		std::cout << "construct(prepare)" << std::endl;
  12. 	}
  13. 	Test(std::nullptr_t){
  14. 		std::cout << "construct(nullptr)" << std::endl;
  15. 	}
  16. 	Test& operator = (std::nullptr_t){
  17. 		std::cout << "assign(nullptr)" << std::endl;
  18. 		return *this;
  19. 	}
  20. 	Test(const Test& aTest){
  21. 		std::cout << "construct(const self&)" << std::endl;
  22. 		pString = aTest.pString;
  23. 	}
  24. 	Test& operator = (const Test& aTest){
  25. 		std::cout << "assign(const self&)" << std::endl;
  26. 		if(&aTest != this){
  27. 			pString = aTest.pString;
  28. 		}
  29. 		return *this;
  30. 	}
  31. 	Test(Test&& aTest){
  32. 		std::cout << "construct(self&&)" << std::endl;
  33. 		std::swap(pString, aTest.pString);
  34. 	}
  35. 	Test& operator = (Test&& aTest){
  36. 		std::cout << "assign(self&&)" << std::endl;
  37. 		if(&aTest != this){
  38. 			std::swap(pString, aTest.pString);
  39. 		}
  40. 		return *this;
  41. 	}
  42. 	~Test(){
  43. 		std::cout << "destroy" << std::endl;
  44. 	}
  45. };
  46.  
  47. template <typename Output_t, typename ...Input_t>
  48. inline Output_t& Compact(Output_t& aOutput, Input_t&& ...aInput){
  49. 	// should I do this?
  50. 	if(!sizeof...(aInput)){
  51. 		return aOutput;
  52. 	}
  53.  
  54. 	// I like typedefs as they shorten the code :)
  55. 	typedef typename Output_t::value_type Type_t;
  56.  
  57. 	// can be either lvalues or rvalues in the initializer_list when it's populated.
  58. 	std::initializer_list<Type_t> vInput = { std::forward<Input_t>(aInput)... };
  59.  
  60. 	// now move the initializer_list into the vector.
  61. 	aOutput.reserve(aOutput.size() + vInput.size());
  62. 	for(auto vIter(vInput.begin()), vEnd(vInput.end()); vIter != vEnd; ++vIter){
  63. 		// move (don't copy) out the lvalue or rvalue out of the initializer_list.
  64. 		aOutput.emplace_back(std::move(const_cast<Type_t&>(*vIter))); // <- THIS!
  65. 	}
  66.  
  67. 	// done! :)
  68. 	return aOutput;
  69. }
  70.  
  71.  
  72. int main() {
  73. 	// assign the values to track both string and memory moves
  74. 	Test vTestL("lvalue"), vTestR("rvalue");
  75. 	// claim 1KB of memory so results are not affected by SSO (small string optimization)
  76. 	vTestL.pString.reserve(1024);
  77. 	vTestR.pString.reserve(1024);
  78.  
  79. 	std::cout << std::endl;
  80. 	std::cout << "Input(before):" << std::endl;
  81. 	std::cout << "LValue: " << vTestL.pString
  82. 		<< " - 0x" << reinterpret_cast<const void*>(vTestL.pString.c_str())
  83. 		<< " -- (should be unscathed)" << std::endl;
  84. 	std::cout << "RValue: " << vTestR.pString
  85. 		<< " - 0x" << reinterpret_cast<const void*>(vTestR.pString.c_str())
  86. 		<< " -- (should be relocated)" << std::endl;
  87. 	std::cout << std::endl;
  88.  
  89. 	std::vector<Test> vTests;
  90. 	Compact(vTests, vTestL, std::move(vTestR));
  91.  
  92. 	std::cout << std::endl;
  93. 	std::cout << "Input(after):" << std::endl;
  94. 	std::cout << "LValue: " << vTestL.pString
  95. 		<< " - 0x" << reinterpret_cast<const void*>(vTestL.pString.c_str())
  96. 		<< " -- (should be unscathed)" << std::endl;
  97. 	std::cout << "RValue: " << vTestR.pString
  98. 		<< " - 0x" << reinterpret_cast<const void*>(vTestR.pString.c_str())
  99. 		<< " -- (should be relocated)" << std::endl;
  100. 	std::cout << std::endl;
  101.  
  102. 	std::cout << std::endl;
  103. 	std::cout << "Output:" << std::endl;
  104. 	std::cout << "LValue: " << vTests[0].pString
  105. 		<< " - 0x" << reinterpret_cast<const void*>(vTests[0].pString.c_str())
  106. 		<< " -- (should be unscathed)" << std::endl;
  107. 	std::cout << "RValue: " << vTests[1].pString
  108. 		<< " - 0x" << reinterpret_cast<const void*>(vTests[1].pString.c_str())
  109. 		<< " -- (should be unscathed)" << std::endl;
  110. 	std::cout << std::endl;
  111.  
  112. 	return 0;
  113. }
Success #stdin #stdout 0s 3436KB
comments (?)
stdin
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Standard input is empty
stdout
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construct(prepare)
construct(prepare)

Input(before):
LValue: lvalue - 0x0x9957044 -- (should be unscathed)
RValue: rvalue - 0x0x995745c -- (should be relocated)

construct(const self&)
construct(self&&)
construct(self&&)
construct(self&&)
destroy
destroy

Input(after):
LValue: lvalue - 0x0x9957044 -- (should be unscathed)
RValue:  - 0x0x804b62c -- (should be relocated)


Output:
LValue: lvalue - 0x0x9957044
RValue: rvalue - 0x0x995745c

destroy
destroy
destroy
destroy
https://ideone.com/kTn2BC
language:
C++14 (gcc 8.3)
created:
10 years ago
visibility:
public

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