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_<std::remove_cv_t<T>>;
  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_<std::remove_cv_t<T>>;
  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, std::enable_if_t<rt_ && (__VA_ARGS__),bool> = true
  78 #define IS_VALID_CONTAINER(C)                                                 \
  79     !detail_::is_span<C>::value && !detail_::is_std_array<C>::value &&        \
  80     !std::is_array<C>::value && detail_::has_size_and_data<C>::value &&       \
  81     std::is_convertible<std::remove_pointer_t<decltype(al::data(std::declval<C&>()))>(*)[],element_type(*)[]>::value
  82
  83 template<typename T, size_t E>
  84 class span {
  85     static constexpr size_t dynamic_extent{static_cast<size_t>(-1)};
  86
  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 : span{al::data(arr), al::size(arr)} { }
 113     template<typename U, REQUIRES(IS_VALID_CONTAINER(U))>
 114     constexpr span(U &cont) : span{al::data(cont), al::size(cont)} { }
 115     template<typename U, REQUIRES(IS_VALID_CONTAINER(const U))>
 116     constexpr span(const U &cont) : span{al::data(cont), al::size(cont)} { }
 117     template<typename U, REQUIRES(!std::is_same<element_type,U>::value && std::is_convertible<U(*)[],element_type(*)[]>::value)>
 118     constexpr span(const span<U,E> &span_) noexcept : span{al::data(span_), al::size(span_)} { }
 119     constexpr span(const span&) noexcept = default;
 120
 121     span& operator=(const span &rhs) noexcept = default;
 122
 123     constexpr reference front() const { return *mData; }
 124     constexpr reference back() const { return *(mData+E-1); }
 125     constexpr reference operator[](index_type idx) const { return mData[idx]; }
 126     constexpr pointer data() const noexcept { return mData; }
 127
 128     constexpr index_type size() const noexcept { return E; }
 129     constexpr index_type size_bytes() const noexcept { return E * sizeof(value_type); }
 130     constexpr bool empty() const noexcept { return E == 0; }
 131
 132     constexpr iterator begin() const noexcept { return mData; }
 133     constexpr iterator end() const noexcept { return mData+E; }
 134     constexpr const_iterator cbegin() const noexcept { return mData; }
 135     constexpr const_iterator cend() const noexcept { return mData+E; }
 136
 137     constexpr reverse_iterator rbegin() const noexcept { return reverse_iterator{end()}; }
 138     constexpr reverse_iterator rend() const noexcept { return reverse_iterator{begin()}; }
 139     constexpr const_reverse_iterator crbegin() const noexcept { return const_reverse_iterator{cend()}; }
 140     constexpr const_reverse_iterator crend() const noexcept { return const_reverse_iterator{cbegin()}; }
 141
 142     template<size_t C>
 143     constexpr span<element_type,C> first() const
 144     {
 145         static_assert(E >= C, "New size exceeds original capacity");
 146         return span<element_type,C>{mData, C};
 147     }
 148
 149     template<size_t C>
 150     constexpr span<element_type,C> last() const
 151     {
 152         static_assert(E >= C, "New size exceeds original capacity");
 153         return span<element_type,C>{mData+(E-C), C};
 154     }
 155
 156     template<size_t O, size_t C, size_t RealC=((C==dynamic_extent) ? E-O : C)>
 157     constexpr span<element_type,RealC> subspan() const
 158     {
 159         static_assert(E >= O, "Offset exceeds extent");
 160         static_assert(E-O >= RealC, "New size exceeds original capacity");
 161         return span<element_type,RealC>{mData+O, RealC};
 162     }
 163
 164     /* NOTE: Can't declare objects of a specialized template class prior to
 165      * defining the specialization. As a result, these methods need to be
 166      * defined later.
 167      */
 168     constexpr span<element_type,dynamic_extent> first(size_t count) const;
 169     constexpr span<element_type,dynamic_extent> last(size_t count) const;
 170     constexpr span<element_type,dynamic_extent> subspan(size_t offset, size_t count=dynamic_extent) const;
 171
 172 private:
 173     pointer mData{nullptr};
 174 };
 175
 176 template<typename T>
 177 class span<T,static_cast<size_t>(-1)> {
 178     static constexpr size_t dynamic_extent{static_cast<size_t>(-1)};
 179
 180 public:
 181     using element_type = T;
 182     using value_type = std::remove_cv_t<T>;
 183     using index_type = size_t;
 184     using difference_type = ptrdiff_t;
 185
 186     using pointer = T*;
 187     using const_pointer = const T*;
 188     using reference = T&;
 189     using const_reference = const T&;
 190
 191     using iterator = pointer;
 192     using const_iterator = const_pointer;
 193     using reverse_iterator = std::reverse_iterator<iterator>;
 194     using const_reverse_iterator = std::reverse_iterator<const_iterator>;
 195
 196     static constexpr size_t extent{static_cast<size_t>(-1)};
 197
 198     constexpr span() noexcept = default;
 199     constexpr span(pointer ptr, index_type count) : mData{ptr}, mDataEnd{ptr+count} { }
 200     constexpr span(pointer first, pointer last) : mData{first}, mDataEnd{last} { }
 201     template<size_t N>
 202     constexpr span(element_type (&arr)[N]) noexcept : span{al::data(arr), al::size(arr)} { }
 203     template<size_t N>
 204     constexpr span(std::array<value_type,N> &arr) noexcept : span{al::data(arr), al::size(arr)} { }
 205     template<size_t N, REQUIRES(std::is_const<element_type>::value)>
 206     constexpr span(const std::array<value_type,N> &arr) noexcept : span{al::data(arr), al::size(arr)} { }
 207     template<typename U, REQUIRES(IS_VALID_CONTAINER(U))>
 208     constexpr span(U &cont) : span{al::data(cont), al::size(cont)} { }
 209     template<typename U, REQUIRES(IS_VALID_CONTAINER(const U))>
 210     constexpr span(const U &cont) : span{al::data(cont), al::size(cont)} { }
 211     template<typename U, size_t N, REQUIRES((!std::is_same<element_type,U>::value || extent != N) && std::is_convertible<U(*)[],element_type(*)[]>::value)>
 212     constexpr span(const span<U,N> &span_) noexcept : span{al::data(span_), al::size(span_)} { }
 213     constexpr span(const span&) noexcept = default;
 214
 215     span& operator=(const span &rhs) noexcept = default;
 216
 217     constexpr reference front() const { return *mData; }
 218     constexpr reference back() const { return *(mDataEnd-1); }
 219     constexpr reference operator[](index_type idx) const { return mData[idx]; }
 220     constexpr pointer data() const noexcept { return mData; }
 221
 222     constexpr index_type size() const noexcept { return static_cast<index_type>(mDataEnd-mData); }
 223     constexpr index_type size_bytes() const noexcept
 224     { return static_cast<index_type>(mDataEnd-mData) * sizeof(value_type); }
 225     constexpr bool empty() const noexcept { return mData == mDataEnd; }
 226
 227     constexpr iterator begin() const noexcept { return mData; }
 228     constexpr iterator end() const noexcept { return mDataEnd; }
 229     constexpr const_iterator cbegin() const noexcept { return mData; }
 230     constexpr const_iterator cend() const noexcept { return mDataEnd; }
 231
 232     constexpr reverse_iterator rbegin() const noexcept { return reverse_iterator{end()}; }
 233     constexpr reverse_iterator rend() const noexcept { return reverse_iterator{begin()}; }
 234     constexpr const_reverse_iterator crbegin() const noexcept { return const_reverse_iterator{cend()}; }
 235     constexpr const_reverse_iterator crend() const noexcept { return const_reverse_iterator{cbegin()}; }
 236
 237     template<size_t C>
 238     constexpr span<element_type,C> first() const
 239     { return span<element_type,C>{mData, C}; }
 240
 241     constexpr span first(size_t count) const
 242     { return (count >= size()) ? *this : span{mData, mData+count}; }
 243
 244     template<size_t C>
 245     constexpr span<element_type,C> last() const
 246     { return span<element_type,C>{mDataEnd-C, C}; }
 247
 248     constexpr span last(size_t count) const
 249     { return (count >= size()) ? *this : span{mDataEnd-count, mDataEnd}; }
 250
 251     template<size_t O, size_t C=dynamic_extent>
 252     constexpr span<element_type,C> subspan() const
 253     { return span<element_type,C>{mData+O, (C!=dynamic_extent) ? mData+O+C : mDataEnd}; }
 254
 255     constexpr span subspan(size_t offset, size_t count=dynamic_extent) const
 256     {
 257         return (offset > size()) ? span{} :
 258             (count >= size()-offset) ? span{mData+offset, mDataEnd} :
 259             span{mData+offset, mData+offset+count};
 260     }
 261
 262 private:
 263     pointer mData{nullptr};
 264     pointer mDataEnd{nullptr};
 265 };
 266
 267 template<typename T, size_t E>
 268 constexpr inline auto span<T,E>::first(size_t count) const -> span<element_type,dynamic_extent>
 269 {
 270     return (count >= size()) ? span<element_type>{mData, extent} :
 271         span<element_type>{mData, count};
 272 }
 273
 274 template<typename T, size_t E>
 275 constexpr inline auto span<T,E>::last(size_t count) const -> span<element_type,dynamic_extent>
 276 {
 277     return (count >= size()) ? span<element_type>{mData, extent} :
 278         span<element_type>{mData+extent-count, count};
 279 }
 280
 281 template<typename T, size_t E>
 282 constexpr inline auto span<T,E>::subspan(size_t offset, size_t count) const -> span<element_type,dynamic_extent>
 283 {
 284     return (offset > size()) ? span<element_type>{} :
 285         (count >= size()-offset) ? span<element_type>{mData+offset, mData+extent} :
 286         span<element_type>{mData+offset, mData+offset+count};
 287 }
 288
 289 #undef IS_VALID_CONTAINER
 290 #undef REQUIRES
 291
 292 } // namespace al
 293
 294 #endif /* AL_SPAN_H */