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  1. #include <cassert>
  2.  
  3. #include <iostream>
  4. #include <iterator>
  5. #include <vector>
  6.  
  7. template <typename C>
  8. struct iterator { using type = typename C::iterator; };
  9.  
  10. template <typename C>
  11. struct iterator<C const> { using type = typename C::const_iterator; };
  12.  
  13. template <typename C>
  14. class ForwardRange {
  15. 	using Iter = typename iterator<C>::type;
  16. public:
  17. 	using pointer = typename std::iterator_traits<Iter>::pointer;
  18.     using reference = typename std::iterator_traits<Iter>::reference;
  19.     using value_type = typename std::iterator_traits<Iter>::value_type;
  20.  
  21. 	ForwardRange(): _begin(), _end() {}
  22.  
  23. 	explicit ForwardRange(C& c): _begin(begin(c)), _end(end(c)) {}
  24.  
  25. 	// Observers
  26. 	explicit operator bool() const { return _begin != _end; }
  27.  
  28. 	reference operator*() const { assert(*this); return *_begin; }
  29. 	pointer operator->() const { assert(*this); return &*_begin; }
  30.  
  31. 	// Modifiers
  32. 	ForwardRange& operator++() { assert(*this); ++_begin; return *this; }
  33. 	ForwardRange operator++(int) { ForwardRange tmp(*this); ++*this; return tmp; }
  34.  
  35. private:
  36. 	Iter _begin;
  37. 	Iter _end;
  38. }; // class ForwardRange
  39.  
  40. template <typename C, size_t N>
  41. class FlattenedForwardRange {
  42. 	using Iter = typename iterator<C>::type;
  43. 	using Inner = FlattenedForwardRange<typename std::iterator_traits<Iter>::value_type, N-1>;
  44. public:
  45. 	using pointer = typename Inner::pointer;
  46. 	using reference = typename Inner::reference;
  47. 	using value_type = typename Inner::value_type;
  48.  
  49. 	FlattenedForwardRange(): _outer(), _inner() {}
  50.  
  51. 	explicit FlattenedForwardRange(C& outer): _outer(outer), _inner() {
  52. 		if (not _outer) { return; }
  53. 		_inner = Inner{*_outer};
  54. 		this->advance();
  55. 	}
  56.  
  57. 	// Observers
  58. 	explicit operator bool() const { return static_cast<bool>(_outer); }
  59.  
  60. 	reference operator*() const { assert(*this); return *_inner; }
  61. 	pointer operator->() const { assert(*this); return _inner.operator->(); }
  62.  
  63. 	// Modifiers
  64. 	FlattenedForwardRange& operator++() { ++_inner; this->advance(); return *this; }
  65. 	FlattenedForwardRange operator++(int) { FlattenedForwardRange tmp(*this); ++*this; return tmp; }
  66.  
  67. private:
  68. 	void advance() {
  69. 		if (_inner) { return; }
  70.  
  71. 		for (++_outer; _outer; ++_outer) {
  72. 			_inner = Inner{*_outer};
  73. 			if (_inner) { return; }
  74. 		}
  75. 		_inner = Inner{};
  76. 	}
  77.  
  78. 	ForwardRange<C> _outer;
  79. 	Inner _inner;
  80. }; // class FlattenedForwardRange
  81.  
  82. template <typename C>
  83. class FlattenedForwardRange<C, 0> {
  84. 	using Iter = typename iterator<C>::type;
  85. public:
  86. 	using pointer = typename std::iterator_traits<Iter>::pointer;
  87.     using reference = typename std::iterator_traits<Iter>::reference;
  88.     using value_type = typename std::iterator_traits<Iter>::value_type;
  89.  
  90. 	FlattenedForwardRange(): _range() {}
  91.  
  92. 	explicit FlattenedForwardRange(C& c): _range(c) {}
  93.  
  94. 	// Observers
  95. 	explicit operator bool() const { return static_cast<bool>(_range); }
  96.  
  97. 	reference operator*() const { return *_range; }
  98. 	pointer operator->() const { return _range.operator->(); }
  99.  
  100. 	// Modifiers
  101. 	FlattenedForwardRange& operator++() { ++_range; return *this; }
  102. 	FlattenedForwardRange operator++(int) { FlattenedForwardRange tmp(*this); ++*this; return tmp; }
  103.  
  104. private:
  105. 	ForwardRange<C> _range;
  106. }; // class FlattenedForwardRange
  107.  
  108. int main() {
  109. 	// Forward Range test
  110. 	std::vector<int> vec{ 1, 2, 3, 4 };
  111. 	for (ForwardRange<std::vector<int>> fr(vec); fr; ++fr) { std::cout << *fr << "\n"; }
  112.  
  113. 	// Flattened Forward Range test
  114. 	std::vector<std::vector<int>> vecvec{ { 1, 2, 3, 4 }, {}, { 5, 6 } };
  115. 	for (FlattenedForwardRange<std::vector<std::vector<int>>, 1> ffr(vecvec); ffr; ++ffr) {
  116. 		std::cout << *ffr << "\n";
  117. 	}
  118. 	return 0;
  119. }
Success #stdin #stdout 0.01s 5292KB
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https://ideone.com/cuQ976
language:
C++14 (gcc 8.3)
created:
5 days ago
visibility:
public

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