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  1. #include <cstdio>
  2. #include <cassert>
  3. #include <iostream>
  4. #include <type_traits>
  5. #include <functional>
  6. using namespace std;
  7.  
  8. template<class RangeType>
  9. struct range_iterator
  10. {
  11. 	RangeType* _range;
  12.  
  13. 	bool operator!=(const range_iterator<RangeType>& that) const {
  14. 		assert(_range == that._range);
  15. 		return !_range->empty();
  16. 	}
  17.  
  18. 	void operator++() {
  19. 		_range->popFront();
  20. 	}
  21.  
  22. 	typename RangeType::value_type operator*() const {
  23. 		return _range->front();
  24. 	}
  25. };
  26.  
  27. template<class T>
  28. struct iota
  29. {
  30. 	typedef T value_type;
  31.  
  32. 	T first;
  33. 	T last;
  34.  
  35. 	iota(T first, T last)
  36. 		: first(first), last(last) {}
  37.  
  38. 	T front() const {
  39. 		return first;
  40. 	}
  41.  
  42. 	void popFront() {
  43. 		++first;
  44. 	}
  45.  
  46. 	bool empty() const {
  47. 		return first == last;
  48. 	}
  49.  
  50. 	typedef range_iterator<iota<T>> iterator;
  51. 	iterator begin() { return iterator{this}; }
  52. 	iterator end() { return iterator{this}; }
  53.  
  54. 	template<template<class InputRange> class RTy, class... Args>
  55. 	RTy<iota<T>> to(Args... args) {
  56. 		return RTy<iota<T>>(*this, args...);
  57. 	}
  58. };
  59.  
  60. template<class R>
  61. struct take
  62. {
  63. 	typedef typename R::value_type value_type;
  64.  
  65. 	R r;
  66. 	int count;
  67.  
  68. 	take(R r, int count)
  69. 		: r(r), count(count){}
  70.  
  71. 	value_type front() const {
  72. 		return r.front();
  73. 	}
  74.  
  75. 	void popFront() {
  76. 		--count;
  77. 		r.popFront();
  78. 	}
  79.  
  80. 	bool empty() const {
  81. 		return r.empty() || count == 0;
  82. 	}
  83.  
  84. 	typedef range_iterator<take<R>> iterator;
  85. 	iterator begin() { return iterator{this}; }
  86. 	iterator end() { return iterator{this}; }
  87.  
  88. 	template<template<class InputRange> class RTy, class... Args>
  89. 	RTy<take<R>> to(Args... args) {
  90. 		return RTy<take<R>>(*this, args...);
  91. 	}
  92. };
  93.  
  94. template<class R>
  95. struct filter
  96. {
  97. 	typedef typename R::value_type value_type;
  98.  
  99. 	R r;
  100. 	function<bool(value_type)> pred;
  101.  
  102. 	filter(R r, const function<bool(value_type)> &pred)
  103. 		: r(r), pred(pred)
  104. 	{
  105. 		while(!r.empty() && !pred(r.front())) {
  106. 			r.popFront();
  107. 		}
  108. 	}
  109.  
  110. 	value_type front() const {
  111. 		return r.front();
  112. 	}
  113.  
  114. 	void popFront() {
  115. 		r.popFront();
  116.  
  117. 		while(!r.empty() && !pred(r.front())) {
  118. 			r.popFront();
  119. 		}
  120. 	}
  121.  
  122. 	bool empty() const {
  123. 		return r.empty();
  124. 	}
  125.  
  126. 	typedef range_iterator<filter<R>> iterator;
  127. 	iterator begin() { return iterator{this}; }
  128. 	iterator end() { return iterator{this}; }
  129. };
  130.  
  131. int main(int argc, const char * argv[])
  132. {
  133. 	auto r = iota<int>(0, 10)
  134. 		.to<take>(6)
  135. 		.to<filter>([](int x){ return !(x % 2); });
  136.  
  137. 	for(int x : r)
  138. 		printf("%d ", x);
  139.  
  140. 	return 0;
  141. }
  142.  
Success #stdin #stdout 0s 3460KB
comments (?)
stdin 
Standard input is empty
stdout 
0 2 4
https://ideone.com/X1JAEn
language:
C++14 (gcc 8.3)
created:
9 years ago
visibility:
public

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