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) noexcept(noexcept(cont.size())) -> decltype(cont.size())
  14 { return cont.size(); }
  15
  16 template<typename T>
  17 constexpr auto size(const T &cont) noexcept(noexcept(cont.size())) -> 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) noexcept(noexcept(cont.data())) -> decltype(cont.data())
  31 { return cont.data(); }
  32
  33 template<typename T>
  34 constexpr auto data(const T &cont) noexcept(noexcept(cont.data())) -> 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 constexpr size_t dynamic_extent{static_cast<size_t>(-1)};
  47
  48 template<typename T, size_t E=dynamic_extent>
  49 class span;
  50
  51 namespace detail_ {
  52     template<typename... Ts>
  53     struct make_void { using type = void; };
  54     template<typename... Ts>
  55     using void_t = typename make_void<Ts...>::type;
  56
  57     template<typename T>
  58     struct is_span_ : std::false_type { };
  59     template<typename T, size_t E>
  60     struct is_span_<span<T,E>> : std::true_type { };
  61     template<typename T>
  62     using is_span = is_span_<std::remove_cv_t<T>>;
  63
  64     template<typename T>
  65     struct is_std_array_ : std::false_type { };
  66     template<typename T, size_t N>
  67     struct is_std_array_<std::array<T,N>> : std::true_type { };
  68     template<typename T>
  69     using is_std_array = is_std_array_<std::remove_cv_t<T>>;
  70
  71     template<typename T, typename = void>
  72     struct has_size_and_data : std::false_type { };
  73     template<typename T>
  74     struct has_size_and_data<T,
  75         void_t<decltype(al::size(std::declval<T>())), decltype(al::data(std::declval<T>()))>>
  76         : std::true_type { };
  77 } // namespace detail_
  78
  79 #define REQUIRES(...) bool rt_=true, std::enable_if_t<rt_ && (__VA_ARGS__),bool> = true
  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     std::is_convertible<std::remove_pointer_t<decltype(al::data(std::declval<C&>()))>(*)[],element_type(*)[]>::value
  84
  85 template<typename T, size_t E>
  86 class span {
  87 public:
  88     using element_type = T;
  89     using value_type = std::remove_cv_t<T>;
  90     using index_type = size_t;
  91     using difference_type = ptrdiff_t;
  92
  93     using pointer = T*;
  94     using const_pointer = const T*;
  95     using reference = T&;
  96     using const_reference = const T&;
  97
  98     using iterator = pointer;
  99     using const_iterator = const_pointer;
 100     using reverse_iterator = std::reverse_iterator<iterator>;
 101     using const_reverse_iterator = std::reverse_iterator<const_iterator>;
 102
 103     static constexpr size_t extent{E};
 104
 105     template<REQUIRES(extent==0)>
 106     constexpr span() noexcept { }
 107     constexpr span(pointer ptr, index_type /*count*/) : mData{ptr} { }
 108     constexpr span(pointer first, pointer /*last*/) : mData{first} { }
 109     constexpr span(element_type (&arr)[E]) noexcept : span{al::data(arr), al::size(arr)} { }
 110     constexpr span(std::array<value_type,E> &arr) noexcept : span{al::data(arr), al::size(arr)} { }
 111     template<REQUIRES(std::is_const<element_type>::value)>
 112     constexpr span(const std::array<value_type,E> &arr) noexcept
 113       : span{al::data(arr), al::size(arr)}
 114     { }
 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
 120         && std::is_convertible<U(*)[],element_type(*)[]>::value)>
 121     constexpr span(const span<U,E> &span_) noexcept : span{al::data(span_), al::size(span_)} { }
 122     constexpr span(const span&) noexcept = default;
 123
 124     constexpr span& operator=(const span &rhs) noexcept = default;
 125
 126     constexpr reference front() const { return *mData; }
 127     constexpr reference back() const { return *(mData+E-1); }
 128     constexpr reference operator[](index_type idx) const { return mData[idx]; }
 129     constexpr pointer data() const noexcept { return mData; }
 130
 131     constexpr index_type size() const noexcept { return E; }
 132     constexpr index_type size_bytes() const noexcept { return E * sizeof(value_type); }
 133     constexpr bool empty() const noexcept { return E == 0; }
 134
 135     constexpr iterator begin() const noexcept { return mData; }
 136     constexpr iterator end() const noexcept { return mData+E; }
 137     constexpr const_iterator cbegin() const noexcept { return mData; }
 138     constexpr const_iterator cend() const noexcept { return mData+E; }
 139
 140     constexpr reverse_iterator rbegin() const noexcept { return reverse_iterator{end()}; }
 141     constexpr reverse_iterator rend() const noexcept { return reverse_iterator{begin()}; }
 142     constexpr const_reverse_iterator crbegin() const noexcept
 143     { return const_reverse_iterator{cend()}; }
 144     constexpr const_reverse_iterator crend() const noexcept
 145     { return const_reverse_iterator{cbegin()}; }
 146
 147     template<size_t C>
 148     constexpr span<element_type,C> first() const
 149     {
 150         static_assert(E >= C, "New size exceeds original capacity");
 151         return span<element_type,C>{mData, C};
 152     }
 153
 154     template<size_t C>
 155     constexpr span<element_type,C> last() const
 156     {
 157         static_assert(E >= C, "New size exceeds original capacity");
 158         return span<element_type,C>{mData+(E-C), C};
 159     }
 160
 161     template<size_t O, size_t C>
 162     constexpr auto subspan() const -> std::enable_if_t<C!=dynamic_extent,span<element_type,C>>
 163     {
 164         static_assert(E >= O, "Offset exceeds extent");
 165         static_assert(E-O >= C, "New size exceeds original capacity");
 166         return span<element_type,C>{mData+O, C};
 167     }
 168
 169     template<size_t O, size_t C=dynamic_extent>
 170     constexpr auto subspan() const -> std::enable_if_t<C==dynamic_extent,span<element_type,E-O>>
 171     {
 172         static_assert(E >= O, "Offset exceeds extent");
 173         return span<element_type,E-O>{mData+O, E-O};
 174     }
 175
 176     /* NOTE: Can't declare objects of a specialized template class prior to
 177      * defining the specialization. As a result, these methods need to be
 178      * defined later.
 179      */
 180     constexpr span<element_type,dynamic_extent> first(size_t count) const;
 181     constexpr span<element_type,dynamic_extent> last(size_t count) const;
 182     constexpr span<element_type,dynamic_extent> subspan(size_t offset,
 183         size_t count=dynamic_extent) const;
 184
 185 private:
 186     pointer mData{nullptr};
 187 };
 188
 189 template<typename T>
 190 class span<T,dynamic_extent> {
 191 public:
 192     using element_type = T;
 193     using value_type = std::remove_cv_t<T>;
 194     using index_type = size_t;
 195     using difference_type = ptrdiff_t;
 196
 197     using pointer = T*;
 198     using const_pointer = const T*;
 199     using reference = T&;
 200     using const_reference = const T&;
 201
 202     using iterator = pointer;
 203     using const_iterator = const_pointer;
 204     using reverse_iterator = std::reverse_iterator<iterator>;
 205     using const_reverse_iterator = std::reverse_iterator<const_iterator>;
 206
 207     static constexpr size_t extent{dynamic_extent};
 208
 209     constexpr span() noexcept = default;
 210     constexpr span(pointer ptr, index_type count) : mData{ptr}, mDataEnd{ptr+count} { }
 211     constexpr span(pointer first, pointer last) : mData{first}, mDataEnd{last} { }
 212     template<size_t N>
 213     constexpr span(element_type (&arr)[N]) noexcept : span{al::data(arr), al::size(arr)} { }
 214     template<size_t N>
 215     constexpr span(std::array<value_type,N> &arr) noexcept : span{al::data(arr), al::size(arr)} { }
 216     template<size_t N, REQUIRES(std::is_const<element_type>::value)>
 217     constexpr span(const std::array<value_type,N> &arr) noexcept
 218       : span{al::data(arr), al::size(arr)}
 219     { }
 220     template<typename U, REQUIRES(IS_VALID_CONTAINER(U))>
 221     constexpr span(U &cont) : span{al::data(cont), al::size(cont)} { }
 222     template<typename U, REQUIRES(IS_VALID_CONTAINER(const U))>
 223     constexpr span(const U &cont) : span{al::data(cont), al::size(cont)} { }
 224     template<typename U, size_t N, REQUIRES((!std::is_same<element_type,U>::value || extent != N)
 225         && std::is_convertible<U(*)[],element_type(*)[]>::value)>
 226     constexpr span(const span<U,N> &span_) noexcept : span{al::data(span_), al::size(span_)} { }
 227     constexpr span(const span&) noexcept = default;
 228
 229     constexpr span& operator=(const span &rhs) noexcept = default;
 230
 231     constexpr reference front() const { return *mData; }
 232     constexpr reference back() const { return *(mDataEnd-1); }
 233     constexpr reference operator[](index_type idx) const { return mData[idx]; }
 234     constexpr pointer data() const noexcept { return mData; }
 235
 236     constexpr index_type size() const noexcept { return static_cast<index_type>(mDataEnd-mData); }
 237     constexpr index_type size_bytes() const noexcept
 238     { return static_cast<index_type>(mDataEnd-mData) * sizeof(value_type); }
 239     constexpr bool empty() const noexcept { return mData == mDataEnd; }
 240
 241     constexpr iterator begin() const noexcept { return mData; }
 242     constexpr iterator end() const noexcept { return mDataEnd; }
 243     constexpr const_iterator cbegin() const noexcept { return mData; }
 244     constexpr const_iterator cend() const noexcept { return mDataEnd; }
 245
 246     constexpr reverse_iterator rbegin() const noexcept { return reverse_iterator{end()}; }
 247     constexpr reverse_iterator rend() const noexcept { return reverse_iterator{begin()}; }
 248     constexpr const_reverse_iterator crbegin() const noexcept
 249     { return const_reverse_iterator{cend()}; }
 250     constexpr const_reverse_iterator crend() const noexcept
 251     { return const_reverse_iterator{cbegin()}; }
 252
 253     template<size_t C>
 254     constexpr span<element_type,C> first() const
 255     { return span<element_type,C>{mData, C}; }
 256
 257     constexpr span first(size_t count) const
 258     { return (count >= size()) ? *this : span{mData, mData+count}; }
 259
 260     template<size_t C>
 261     constexpr span<element_type,C> last() const
 262     { return span<element_type,C>{mDataEnd-C, C}; }
 263
 264     constexpr span last(size_t count) const
 265     { return (count >= size()) ? *this : span{mDataEnd-count, mDataEnd}; }
 266
 267     template<size_t O, size_t C>
 268     constexpr auto subspan() const -> std::enable_if_t<C!=dynamic_extent,span<element_type,C>>
 269     { return span<element_type,C>{mData+O, C}; }
 270
 271     template<size_t O, size_t C=dynamic_extent>
 272     constexpr auto subspan() const -> std::enable_if_t<C==dynamic_extent,span<element_type,C>>
 273     { return span<element_type,C>{mData+O, mDataEnd}; }
 274
 275     constexpr span subspan(size_t offset, size_t count=dynamic_extent) const
 276     {
 277         return (offset > size()) ? span{} :
 278             (count >= size()-offset) ? span{mData+offset, mDataEnd} :
 279             span{mData+offset, mData+offset+count};
 280     }
 281
 282 private:
 283     pointer mData{nullptr};
 284     pointer mDataEnd{nullptr};
 285 };
 286
 287 template<typename T, size_t E>
 288 constexpr inline auto span<T,E>::first(size_t count) const -> span<element_type,dynamic_extent>
 289 {
 290     return (count >= size()) ? span<element_type>{mData, extent} :
 291         span<element_type>{mData, count};
 292 }
 293
 294 template<typename T, size_t E>
 295 constexpr inline auto span<T,E>::last(size_t count) const -> span<element_type,dynamic_extent>
 296 {
 297     return (count >= size()) ? span<element_type>{mData, extent} :
 298         span<element_type>{mData+extent-count, count};
 299 }
 300
 301 template<typename T, size_t E>
 302 constexpr inline auto span<T,E>::subspan(size_t offset, size_t count) const
 303     -> span<element_type,dynamic_extent>
 304 {
 305     return (offset > size()) ? span<element_type>{} :
 306         (count >= size()-offset) ? span<element_type>{mData+offset, mData+extent} :
 307         span<element_type>{mData+offset, mData+offset+count};
 308 }
 309
 310 #undef IS_VALID_CONTAINER
 311 #undef REQUIRES
 312
 313 } // namespace al
 314
 315 #endif /* AL_SPAN_H */