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  1. #include <cstdio>
  2. #include <cassert>
  3. #include <iostream>
  4. using namespace std;
  5.  
  6. template<class T>
  7. struct iota
  8. {
  9. 	T first;
  10. 	T last;
  11.  
  12. 	iota(T first, T last)
  13. 		: first(first), last(last) {}
  14.  
  15. 	T front() const {
  16. 		return first;
  17. 	}
  18.  
  19. 	void popFront() {
  20. 		++first;
  21. 	}
  22.  
  23. 	bool empty() const {
  24. 		return first == last;
  25. 	}
  26.  
  27. 	struct iterator
  28. 	{
  29. 		iota *_iota;
  30.  
  31. 		bool operator!=(const iterator& that) const {
  32. 			assert(_iota == that._iota);
  33. 			return !_iota->empty();
  34. 		}
  35.  
  36. 		void operator++() {
  37. 			_iota->popFront();
  38. 		}
  39.  
  40. 		T operator*() const {
  41. 			return _iota->front();
  42. 		}
  43. 	};
  44.  
  45. 	iterator begin() { return iterator{this}; }
  46. 	iterator end() { return iterator{this}; }
  47.  
  48. 	template<template<class _T, class S> class R, class... Args>
  49. 	R<T, iota<T>> to(Args... args) {
  50. 		return R<T, iota<T>>(args..., this);
  51. 	}
  52. };
  53.  
  54. template<class T, class R>
  55. struct take
  56. {
  57. 	R* r;
  58. 	int count;
  59.  
  60. 	take(int count, R* r) : r(r), count(count){}
  61.  
  62. 	T front() const {
  63. 		return r->front();
  64. 	}
  65.  
  66. 	void popFront() {
  67. 		--count;
  68. 		r->popFront();
  69. 	}
  70.  
  71. 	bool empty() const {
  72. 		return r->empty() || count == 0;
  73. 	}
  74.  
  75. 	struct iterator
  76. 	{
  77. 		take *_take;
  78.  
  79. 		bool operator!=(const iterator& that) const {
  80. 			assert(_take == that._take);
  81. 			return !_take->empty();
  82. 		}
  83.  
  84. 		void operator++() {
  85. 			_take->popFront();
  86. 		}
  87.  
  88. 		T operator*() const {
  89. 			return _take->front();
  90. 		}
  91. 	};
  92.  
  93. 	iterator begin() { return iterator{this}; }
  94. 	iterator end() { return iterator{this}; }
  95. };
  96.  
  97. int main(int argc, const char * argv[])
  98. {
  99. 	for(int x : iota<int>(0, 5).to<take>(3))
  100. 		printf("%d ", x);
  101.  
  102.     return 0;
  103. }
Success #stdin #stdout 0s 3452KB
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https://ideone.com/RoJxLa
language:
C++14 (gcc 8.3)
created:
8 years ago
visibility:
public

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