common/alspan.h

   1 #ifndef AL_SPAN_H
   2 #define AL_SPAN_H
   3
   4 #include <array>
   5 #include <cstddef>
   6 #include <initializer_list>
   7 #include <iterator>
   8 #include <type_traits>
   9
  10 namespace al {
  11
  12 template<typename T>
  13 constexpr auto size(T &cont) -> decltype(cont.size())
  14 { return cont.size(); }
  15
  16 template<typename T>
  17 constexpr auto size(const T &cont) -> decltype(cont.size())
  18 { return cont.size(); }
  19
  20 template<typename T, size_t N>
  21 constexpr size_t size(T (&)[N]) noexcept
  22 { return N; }
  23
  24 template<typename T>
  25 constexpr size_t size(std::initializer_list<T> list) noexcept
  26 { return list.size(); }
  27
  28
  29 template<typename T>
  30 constexpr auto data(T &cont) -> decltype(cont.data())
  31 { return cont.data(); }
  32
  33 template<typename T>
  34 constexpr auto data(const T &cont) -> decltype(cont.data())
  35 { return cont.data(); }
  36
  37 template<typename T, size_t N>
  38 constexpr T* data(T (&arr)[N]) noexcept
  39 { return arr; }
  40
  41 template<typename T>
  42 constexpr const T* data(std::initializer_list<T> list) noexcept
  43 { return list.begin(); }
  44
  45
  46 template<typename T, size_t E=static_cast<size_t>(-1)>
  47 class span;
  48
  49 namespace detail_ {
  50     template<typename... Ts>
  51     struct make_void { using type = void; };
  52     template<typename... Ts>
  53     using void_t = typename make_void<Ts...>::type;
  54
  55     template<typename T>
  56     struct is_span_ : std::false_type { };
  57     template<typename T, size_t E>
  58     struct is_span_<span<T,E>> : std::true_type { };
  59     template<typename T>
  60     using is_span = is_span_<typename std::remove_cv<T>::type>;
  61
  62     template<typename T>
  63     struct is_std_array_ : std::false_type { };
  64     template<typename T, size_t N>
  65     struct is_std_array_<std::array<T,N>> : std::true_type { };
  66     template<typename T>
  67     using is_std_array = is_std_array_<typename std::remove_cv<T>::type>;
  68
  69     template<typename T, typename = void>
  70     struct has_size_and_data : std::false_type { };
  71     template<typename T>
  72     struct has_size_and_data<T,
  73         void_t<decltype(al::size(std::declval<T>())), decltype(al::data(std::declval<T>()))>>
  74         : std::true_type { };
  75 } // namespace detail_
  76
  77 #define REQUIRES(...) bool rt_=true, typename std::enable_if<rt_ && (__VA_ARGS__),bool>::type = true
  78 #define USABLE_CONTAINER_DATA(...)                                            \
  79     std::is_convertible<typename std::remove_pointer<decltype(al::data(std::declval<__VA_ARGS__>()))>::type(*)[],element_type(*)[]>::value
  80 #define IS_VALID_CONTAINER(C)                                                 \
  81     !detail_::is_span<C>::value && !detail_::is_std_array<C>::value &&        \
  82     !std::is_array<C>::value && detail_::has_size_and_data<C>::value &&       \
  83     USABLE_CONTAINER_DATA(C&)
  84
  85 template<typename T, size_t E>
  86 class span {
  87     static constexpr size_t dynamic_extent{static_cast<size_t>(-1)};
  88
  89 public:
  90     using element_type = T;
  91     using value_type = typename std::remove_cv<T>::type;
  92     using index_type = size_t;
  93     using difference_type = ptrdiff_t;
  94
  95     using pointer = T*;
  96     using const_pointer = const T*;
  97     using reference = T&;
  98     using const_reference = const T&;
  99
 100     using iterator = pointer;
 101     using const_iterator = const_pointer;
 102     using reverse_iterator = std::reverse_iterator<iterator>;
 103     using const_reverse_iterator = std::reverse_iterator<const_iterator>;
 104
 105     static constexpr size_t extent{E};
 106
 107     template<REQUIRES(extent==0)>
 108     constexpr span() noexcept { }
 109     constexpr span(pointer ptr, index_type /*count*/) : mData{ptr} { }
 110     constexpr span(pointer first, pointer /*last*/) : mData{first} { }
 111     constexpr span(element_type (&arr)[E]) noexcept : span{al::data(arr), al::size(arr)} { }
 112     constexpr span(std::array<value_type,E> &arr) noexcept : span{al::data(arr), al::size(arr)} { }
 113     template<REQUIRES(std::is_const<element_type>::value)>
 114     constexpr span(const std::array<value_type,E> &arr) noexcept : span{al::data(arr), al::size(arr)} { }
 115     template<typename U, REQUIRES(IS_VALID_CONTAINER(U))>
 116     constexpr span(U &cont) : span{al::data(cont), al::size(cont)} { }
 117     template<typename U, REQUIRES(IS_VALID_CONTAINER(const U))>
 118     constexpr span(const U &cont) : span{al::data(cont), al::size(cont)} { }
 119     template<typename U, REQUIRES(!std::is_same<element_type,U>::value && std::is_convertible<U(*)[],element_type(*)[]>::value)>
 120     constexpr span(const span<U,E> &span_) noexcept : span{al::data(span_), al::size(span_)} { }
 121     constexpr span(const span&) noexcept = default;
 122
 123     span& operator=(const span &rhs) noexcept = default;
 124
 125     constexpr reference front() const { return *mData; }
 126     constexpr reference back() const { return *(mData+E-1); }
 127     constexpr reference operator[](index_type idx) const { return mData[idx]; }
 128     constexpr pointer data() const noexcept { return mData; }
 129
 130     constexpr index_type size() const noexcept { return E; }
 131     constexpr index_type size_bytes() const noexcept { return E * sizeof(value_type); }
 132     constexpr bool empty() const noexcept { return E == 0; }
 133
 134     constexpr iterator begin() const noexcept { return mData; }
 135     constexpr iterator end() const noexcept { return mData+E; }
 136     constexpr const_iterator cbegin() const noexcept { return mData; }
 137     constexpr const_iterator cend() const noexcept { return mData+E; }
 138
 139     constexpr reverse_iterator rbegin() const noexcept { return end(); }
 140     constexpr reverse_iterator rend() const noexcept { return begin(); }
 141     constexpr const_reverse_iterator crbegin() const noexcept { return cend(); }
 142     constexpr const_reverse_iterator crend() const noexcept { return cbegin(); }
 143
 144     template<size_t C>
 145     constexpr span<element_type,C> first() const
 146     {
 147         static_assert(E >= C, "New size exceeds original capacity");
 148         return span<element_type,C>{mData, C};
 149     }
 150
 151     template<size_t C>
 152     constexpr span<element_type,C> last() const
 153     {
 154         static_assert(E >= C, "New size exceeds original capacity");
 155         return span<element_type,C>{mData+(E-C), C};
 156     }
 157
 158     template<size_t O, size_t C, size_t RealC=((C==dynamic_extent) ? E-O : C)>
 159     constexpr span<element_type,RealC> subspan() const
 160     {
 161         static_assert(E >= O, "Offset exceeds extent");
 162         static_assert(E-O >= RealC, "New size exceeds original capacity");
 163         return span<element_type,RealC>{mData+O, RealC};
 164     }
 165
 166     /* NOTE: Can't declare objects of a specialized template class prior to
 167      * defining the specialization. As a result, these methods need to be
 168      * defined later.
 169      */
 170     constexpr span<element_type,dynamic_extent> first(size_t count) const;
 171     constexpr span<element_type,dynamic_extent> last(size_t count) const;
 172     constexpr span<element_type,dynamic_extent> subspan(size_t offset, size_t count=dynamic_extent) const;
 173
 174 private:
 175     pointer mData{nullptr};
 176 };
 177
 178 template<typename T>
 179 class span<T,static_cast<size_t>(-1)> {
 180     static constexpr size_t dynamic_extent{static_cast<size_t>(-1)};
 181
 182 public:
 183     using element_type = T;
 184     using value_type = typename std::remove_cv<T>::type;
 185     using index_type = size_t;
 186     using difference_type = ptrdiff_t;
 187
 188     using pointer = T*;
 189     using const_pointer = const T*;
 190     using reference = T&;
 191     using const_reference = const T&;
 192
 193     using iterator = pointer;
 194     using const_iterator = const_pointer;
 195     using reverse_iterator = std::reverse_iterator<iterator>;
 196     using const_reverse_iterator = std::reverse_iterator<const_iterator>;
 197
 198     static constexpr size_t extent{static_cast<size_t>(-1)};
 199
 200     constexpr span() noexcept = default;
 201     constexpr span(pointer ptr, index_type count) : mData{ptr}, mDataEnd{ptr+count} { }
 202     constexpr span(pointer first, pointer last) : mData{first}, mDataEnd{last} { }
 203     template<size_t N>
 204     constexpr span(element_type (&arr)[N]) noexcept : span{al::data(arr), al::size(arr)} { }
 205     template<size_t N>
 206     constexpr span(std::array<value_type,N> &arr) noexcept : span{al::data(arr), al::size(arr)} { }
 207     template<size_t N, REQUIRES(std::is_const<element_type>::value)>
 208     constexpr span(const std::array<value_type,N> &arr) noexcept : span{al::data(arr), al::size(arr)} { }
 209     template<typename U, REQUIRES(IS_VALID_CONTAINER(U))>
 210     constexpr span(U &cont) : span{al::data(cont), al::size(cont)} { }
 211     template<typename U, REQUIRES(IS_VALID_CONTAINER(const U))>
 212     constexpr span(const U &cont) : span{al::data(cont), al::size(cont)} { }
 213     template<typename U, size_t N, REQUIRES((!std::is_same<element_type,U>::value || extent != N) && std::is_convertible<U(*)[],element_type(*)[]>::value)>
 214     constexpr span(const span<U,N> &span_) noexcept : span{al::data(span_), al::size(span_)} { }
 215     constexpr span(const span&) noexcept = default;
 216
 217     span& operator=(const span &rhs) noexcept = default;
 218
 219     constexpr reference front() const { return *mData; }
 220     constexpr reference back() const { return *(mDataEnd-1); }
 221     constexpr reference operator[](index_type idx) const { return mData[idx]; }
 222     constexpr pointer data() const noexcept { return mData; }
 223
 224     constexpr index_type size() const noexcept { return static_cast<index_type>(mDataEnd-mData); }
 225     constexpr index_type size_bytes() const noexcept
 226     { return static_cast<index_type>(mDataEnd-mData) * sizeof(value_type); }
 227     constexpr bool empty() const noexcept { return mData == mDataEnd; }
 228
 229     constexpr iterator begin() const noexcept { return mData; }
 230     constexpr iterator end() const noexcept { return mDataEnd; }
 231     constexpr const_iterator cbegin() const noexcept { return mData; }
 232     constexpr const_iterator cend() const noexcept { return mDataEnd; }
 233
 234     constexpr reverse_iterator rbegin() const noexcept { return end(); }
 235     constexpr reverse_iterator rend() const noexcept { return begin(); }
 236     constexpr const_reverse_iterator crbegin() const noexcept { return cend(); }
 237     constexpr const_reverse_iterator crend() const noexcept { return cbegin(); }
 238
 239     template<size_t C>
 240     constexpr span<element_type,C> first() const
 241     { return span<element_type,C>{mData, C}; }
 242
 243     constexpr span first(size_t count) const
 244     { return (count >= size()) ? *this : span{mData, mData+count}; }
 245
 246     template<size_t C>
 247     constexpr span<element_type,C> last() const
 248     { return span<element_type,C>{mDataEnd-C, C}; }
 249
 250     constexpr span last(size_t count) const
 251     { return (count >= size()) ? *this : span{mDataEnd-count, mDataEnd}; }
 252
 253     template<size_t O, size_t C=dynamic_extent>
 254     constexpr span<element_type,C> subspan() const
 255     { return span<element_type,C>{mData+O, (C!=dynamic_extent) ? mData+C : mDataEnd}; }
 256
 257     constexpr span subspan(size_t offset, size_t count=dynamic_extent) const
 258     {
 259         return (offset > size()) ? span{} :
 260             (count >= size()-offset) ? span{mData+offset, mDataEnd} :
 261             span{mData+offset, mData+offset+count};
 262     }
 263
 264 private:
 265     pointer mData{nullptr};
 266     pointer mDataEnd{nullptr};
 267 };
 268
 269 template<typename T, size_t E>
 270 constexpr inline auto span<T,E>::first(size_t count) const -> span<element_type,dynamic_extent>
 271 {
 272     return (count >= size()) ? span<element_type>{mData, extent} :
 273         span<element_type>{mData, count};
 274 }
 275
 276 template<typename T, size_t E>
 277 constexpr inline auto span<T,E>::last(size_t count) const -> span<element_type,dynamic_extent>
 278 {
 279     return (count >= size()) ? span<element_type>{mData, extent} :
 280         span<element_type>{mData+extent-count, count};
 281 }
 282
 283 template<typename T, size_t E>
 284 constexpr inline auto span<T,E>::subspan(size_t offset, size_t count) const -> span<element_type,dynamic_extent>
 285 {
 286     return (offset > size()) ? span<element_type>{} :
 287         (count >= size()-offset) ? span<element_type>{mData+offset, mData+extent} :
 288         span<element_type>{mData+offset, mData+offset+count};
 289 }
 290
 291 #undef IS_VALID_CONTAINER
 292 #undef USABLE_CONTAINER_DATA
 293 #undef REQUIRES
 294
 295 } // namespace al
 296
 297 #endif /* AL_SPAN_H */