1 /* 2 * Copyright 2019 Google Inc. 3 * 4 * Use of this source code is governed by a BSD-style license that can be 5 * found in the LICENSE file. 6 */ 7 8 #ifndef SkIota_DEFINED 9 #define SkIota_DEFINED 10 11 #include <cstddef> 12 #include <iterator> 13 #include <tuple> 14 15 #include "include/private/SkTLogic.h" 16 17 template <typename Iter, typename C = skstd::monostate> 18 class SkEnumerate { 19 using Captured = decltype(*std::declval<Iter>()); 20 template <typename> struct is_tuple : std::false_type {}; 21 template <typename... T> struct is_tuple<std::tuple<T...>> : std::true_type {}; 22 static constexpr auto MakeResult(size_t i, Captured&& v) { 23 if constexpr (is_tuple<Captured>::value) { 24 return std::tuple_cat(std::tuple<size_t>{i}, std::forward<Captured>(v)); 25 } else { 26 return std::tuple_cat(std::tuple<size_t>{i}, 27 std::make_tuple(std::forward<Captured>(v))); 28 } 29 } 30 using Result = decltype(MakeResult(0, std::declval<Captured>())); 31 32 class Iterator { 33 public: 34 using value_type = Result; 35 using difference_type = ptrdiff_t; 36 using pointer = value_type*; 37 using reference = value_type; 38 using iterator_category = std::input_iterator_tag; 39 constexpr Iterator(ptrdiff_t index, Iter it) : fIndex{index}, fIt{it} { } 40 constexpr Iterator(const Iterator&) = default; 41 constexpr Iterator operator++() { ++fIndex; ++fIt; return *this; } 42 constexpr Iterator operator++(int) { Iterator tmp(*this); operator++(); return tmp; } 43 constexpr bool operator==(const Iterator& rhs) const { return fIt == rhs.fIt; } 44 constexpr bool operator!=(const Iterator& rhs) const { return fIt != rhs.fIt; } 45 constexpr reference operator*() { return MakeResult(fIndex, *fIt); } 46 47 private: 48 ptrdiff_t fIndex; 49 Iter fIt; 50 }; 51 52 public: 53 constexpr SkEnumerate(Iter begin, Iter end) : SkEnumerate{0, begin, end} {} 54 explicit constexpr SkEnumerate(C&& c) 55 : fCollection{std::move(c)} 56 , fBeginIndex{0} 57 , fBegin{std::begin(fCollection)} 58 , fEnd{std::end(fCollection)} { } 59 constexpr SkEnumerate(const SkEnumerate& that) = default; 60 constexpr SkEnumerate& operator=(const SkEnumerate& that) { 61 fBegin = that.fBegin; 62 fEnd = that.fEnd; 63 return *this; 64 } 65 constexpr Iterator begin() const { return Iterator{fBeginIndex, fBegin}; } 66 constexpr Iterator end() const { return Iterator{fBeginIndex + this->ssize(), fEnd}; } 67 constexpr bool empty() const { return fBegin == fEnd; } 68 constexpr size_t size() const { return std::distance(fBegin, fEnd); } 69 constexpr ptrdiff_t ssize() const { return std::distance(fBegin, fEnd); } 70 constexpr SkEnumerate first(size_t n) { 71 SkASSERT(n <= this->size()); 72 ptrdiff_t deltaEnd = this->ssize() - n; 73 return SkEnumerate{fBeginIndex, fBegin, std::prev(fEnd, deltaEnd)}; 74 } 75 constexpr SkEnumerate last(size_t n) { 76 SkASSERT(n <= this->size()); 77 ptrdiff_t deltaBegin = this->ssize() - n; 78 return SkEnumerate{fBeginIndex + deltaBegin, std::next(fBegin, deltaBegin), fEnd}; 79 } 80 constexpr SkEnumerate subspan(size_t offset, size_t count) { 81 SkASSERT(offset < this->size()); 82 SkASSERT(count <= this->size() - offset); 83 auto newBegin = std::next(fBegin, offset); 84 return SkEnumerate(fBeginIndex + offset, newBegin, std::next(newBegin, count)); 85 } 86 87 private: 88 constexpr SkEnumerate(ptrdiff_t beginIndex, Iter begin, Iter end) 89 : fBeginIndex{beginIndex} 90 , fBegin(begin) 91 , fEnd(end) {} 92 93 C fCollection; 94 const ptrdiff_t fBeginIndex; 95 Iter fBegin; 96 Iter fEnd; 97 }; 98 99 template <typename C, typename Iter = decltype(std::begin(std::declval<C>()))> 100 inline constexpr SkEnumerate<Iter> SkMakeEnumerate(C& c) { 101 return SkEnumerate<Iter>{std::begin(c), std::end(c)}; 102 } 103 template <typename C, typename Iter = decltype(std::begin(std::declval<C>()))> 104 inline constexpr SkEnumerate<Iter, C> SkMakeEnumerate(C&& c) { 105 return SkEnumerate<Iter, C>{std::forward<C>(c)}; 106 } 107 108 template <class T, std::size_t N, typename Iter = decltype(std::begin(std::declval<T(&)[N]>()))> 109 inline constexpr SkEnumerate<Iter> SkMakeEnumerate(T (&a)[N]) { 110 return SkEnumerate<Iter>{std::begin(a), std::end(a)}; 111 } 112 #endif // SkIota_DEFINED 113