libstdc++-v3/include/std/span

   1 // Components for manipulating non-owning sequences of objects -*- C++ -*-
   2
   3 // Copyright (C) 2019 Free Software Foundation, Inc.
   4 //
   5 // This file is part of the GNU ISO C++ Library.  This library is free
   6 // software; you can redistribute it and/or modify it under the
   7 // terms of the GNU General Public License as published by the
   8 // Free Software Foundation; either version 3, or (at your option)
   9 // any later version.
  10
  11 // This library is distributed in the hope that it will be useful,
  12 // but WITHOUT ANY WARRANTY; without even the implied warranty of
  13 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14 // GNU General Public License for more details.
  15
  16 // Under Section 7 of GPL version 3, you are granted additional
  17 // permissions described in the GCC Runtime Library Exception, version
  18 // 3.1, as published by the Free Software Foundation.
  19
  20 // You should have received a copy of the GNU General Public License and
  21 // a copy of the GCC Runtime Library Exception along with this program;
  22 // see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
  23 // <http://www.gnu.org/licenses/>.
  24
  25 /** @file span
  26  *  This is a Standard C++ Library header.
  27  */
  28
  29 //
  30 // P0122 span library
  31 // Contributed by ThePhD
  32 //
  33
  34 #ifndef _GLIBCXX_SPAN
  35 #define _GLIBCXX_SPAN 1
  36
  37 #pragma GCC system_header
  38
  39 #if __cplusplus > 201703L
  40
  41 #include <type_traits>
  42 #include <array>
  43 #include <bits/stl_iterator.h>
  44 #include <bits/range_access.h>
  45
  46 #if __cpp_lib_concepts
  47 namespace std _GLIBCXX_VISIBILITY(default)
  48 {
  49 _GLIBCXX_BEGIN_NAMESPACE_VERSION
  50
  51 #define __cpp_lib_span 201902L
  52
  53   inline constexpr size_t dynamic_extent = static_cast<size_t>(-1);
  54
  55   template<typename _Type, size_t _Extent>
  56     class span;
  57
  58   namespace __detail
  59   {
  60     template<typename _Tp>
  61       struct __is_std_span : false_type { };
  62
  63     template<typename _Tp, size_t _Num>
  64       struct __is_std_span<span<_Tp, _Num>> : true_type { };
  65
  66     template<typename _Tp>
  67       struct __is_std_array : false_type { };
  68
  69     template<typename _Tp, size_t _Num>
  70       struct __is_std_array<_GLIBCXX_STD_C::array<_Tp, _Num>> : true_type { };
  71
  72 #ifdef _GLIBCXX_DEBUG
  73     template<typename _Tp, size_t _Num>
  74       struct __is_std_array<__debug::array<_Tp, _Num>> : true_type { };
  75 #endif
  76
  77     template<size_t _Extent>
  78       class __extent_storage
  79       {
  80       public:
  81         constexpr
  82         __extent_storage(size_t) noexcept
  83         { }
  84
  85         static constexpr size_t
  86         _M_extent() noexcept
  87         { return _Extent; }
  88       };
  89
  90     template<>
  91       class __extent_storage<dynamic_extent>
  92       {
  93       public:
  94         constexpr
  95         __extent_storage(size_t __extent) noexcept
  96         : _M_extent_value(__extent)
  97         { }
  98
  99         constexpr size_t
 100         _M_extent() const noexcept
 101         { return this->_M_extent_value; }
 102
 103       private:
 104         size_t _M_extent_value;
 105       };
 106   } // namespace __detail
 107
 108   template<typename _Type, size_t _Extent = dynamic_extent>
 109     class span
 110     {
 111       template<size_t _Offset, size_t _Count>
 112         static constexpr size_t
 113         _S_subspan_extent()
 114         {
 115           if constexpr (_Count != dynamic_extent)
 116             return _Count;
 117           else if constexpr (extent != dynamic_extent)
 118             return _Extent - _Offset;
 119           else
 120             return dynamic_extent;
 121         }
 122
 123       // _GLIBCXX_RESOLVE_LIB_DEFECTS
 124       // 3255. span's array constructor is too strict
 125       template<typename _Tp, size_t _ArrayExtent>
 126         using __is_compatible_array = __and_<
 127           bool_constant<(_Extent == dynamic_extent || _ArrayExtent == _Extent)>,
 128           __is_array_convertible<_Type, _Tp>>;
 129
 130       template<typename _Iter, typename _Ref = iter_reference_t<_Iter>>
 131         using __is_compatible_iterator = __and_<
 132           bool_constant<contiguous_iterator<_Iter>>,
 133           is_lvalue_reference<iter_reference_t<_Iter>>,
 134           is_same<iter_value_t<_Iter>, remove_cvref_t<_Ref>>,
 135           __is_array_convertible<_Type, remove_reference_t<_Ref>>>;
 136
 137       template<typename _Range>
 138         using __is_compatible_range
 139           = __is_compatible_iterator<ranges::iterator_t<_Range>>;
 140
 141     public:
 142       // member types
 143       using value_type             = remove_cv_t<_Type>;
 144       using element_type           = _Type;
 145       using size_type              = size_t;
 146       using reference              = element_type&;
 147       using const_reference        = const element_type&;
 148       using pointer                = _Type*;
 149       using const_pointer          = const _Type*;
 150       using iterator
 151         = __gnu_cxx::__normal_iterator<pointer, span>;
 152       using const_iterator
 153         = __gnu_cxx::__normal_iterator<const_pointer, span>;
 154       using reverse_iterator       = std::reverse_iterator<iterator>;
 155       using const_reverse_iterator = std::reverse_iterator<const_iterator>;
 156       using difference_type        = ptrdiff_t;
 157
 158       // member constants
 159       static inline constexpr size_t extent = _Extent;
 160
 161       // constructors
 162
 163       constexpr
 164       span() noexcept
 165       requires ((_Extent + 1u) <= 1u)
 166       : _M_extent(0), _M_ptr(nullptr)
 167       { }
 168
 169       constexpr
 170       span(const span&) noexcept = default;
 171
 172       template<typename _Tp, size_t _ArrayExtent>
 173         requires (__is_compatible_array<_Tp, _ArrayExtent>::value)
 174         constexpr
 175         span(_Tp (&__arr)[_ArrayExtent]) noexcept
 176         : span(static_cast<pointer>(__arr), _ArrayExtent)
 177         { }
 178
 179       template<typename _Tp, size_t _ArrayExtent>
 180         requires (__is_compatible_array<_Tp, _ArrayExtent>::value)
 181         constexpr
 182         span(array<_Tp, _ArrayExtent>& __arr) noexcept
 183         : span(static_cast<pointer>(__arr.data()), _ArrayExtent)
 184         { }
 185
 186       template<typename _Tp, size_t _ArrayExtent>
 187           requires (__is_compatible_array<const _Tp, _ArrayExtent>::value)
 188         constexpr
 189         span(const array<_Tp, _ArrayExtent>& __arr) noexcept
 190         : span(static_cast<pointer>(__arr.data()), _ArrayExtent)
 191         { }
 192
 193     public:
 194       template<ranges::contiguous_range _Range>
 195         requires (_Extent == dynamic_extent)
 196           && (!__detail::__is_std_span<remove_cvref_t<_Range>>::value)
 197           && (!__detail::__is_std_array<remove_cvref_t<_Range>>::value)
 198           && (!is_array_v<remove_reference_t<_Range>>)
 199           && (__is_compatible_range<_Range>::value)
 200         constexpr
 201         span(_Range&& __range)
 202         noexcept(noexcept(ranges::data(__range))
 203                   && noexcept(ranges::size(__range)))
 204         : span(ranges::data(__range), ranges::size(__range))
 205         { }
 206
 207       template<contiguous_iterator _ContiguousIterator,
 208         sized_sentinel_for<_ContiguousIterator> _Sentinel>
 209           requires (__is_compatible_iterator<_ContiguousIterator>::value)
 210             && (!is_convertible_v<_Sentinel, size_type>)
 211         constexpr
 212         span(_ContiguousIterator __first, _Sentinel __last)
 213         noexcept(noexcept(__last - __first))
 214         : _M_extent(static_cast<size_type>(__last - __first)),
 215           _M_ptr(std::to_address(__first))
 216         {
 217           if (_Extent != dynamic_extent)
 218             __glibcxx_assert((__last - __first) == _Extent);
 219         }
 220
 221       template<contiguous_iterator _ContiguousIterator>
 222         requires (__is_compatible_iterator<_ContiguousIterator>::value)
 223         constexpr
 224         span(_ContiguousIterator __first, size_type __count)
 225         noexcept
 226         : _M_extent(__count), _M_ptr(std::to_address(__first))
 227         { __glibcxx_assert(_Extent == dynamic_extent || __count == _Extent); }
 228
 229       template<typename _OType, size_t _OExtent>
 230         requires (_Extent == dynamic_extent || _Extent == _OExtent)
 231           && (__is_array_convertible<_Type, _OType>::value)
 232         constexpr
 233         span(const span<_OType, _OExtent>& __s) noexcept
 234         : _M_extent(__s.size()), _M_ptr(__s.data())
 235         { }
 236
 237       // assignment
 238
 239       constexpr span&
 240       operator=(const span&) noexcept = default;
 241
 242       // observers
 243
 244       constexpr size_type
 245       size() const noexcept
 246       { return this->_M_extent._M_extent(); }
 247
 248       constexpr size_type
 249       size_bytes() const noexcept
 250       { return this->_M_extent._M_extent() * sizeof(element_type); }
 251
 252       [[nodiscard]] constexpr bool
 253       empty() const noexcept
 254       { return size() == 0; }
 255
 256       // element access
 257
 258       constexpr reference
 259       front() const noexcept
 260       {
 261         static_assert(extent != 0);
 262         __glibcxx_assert(!empty());
 263         return *this->_M_ptr;
 264       }
 265
 266       constexpr reference
 267       back() const noexcept
 268       {
 269         static_assert(extent != 0);
 270         __glibcxx_assert(!empty());
 271         return *(this->_M_ptr + (size() - 1));
 272       }
 273
 274       constexpr reference
 275       operator[](size_type __idx) const noexcept
 276       {
 277         static_assert(extent != 0);
 278         __glibcxx_assert(__idx < size());
 279         return *(this->_M_ptr + __idx);
 280       }
 281
 282       constexpr pointer
 283       data() const noexcept
 284       { return this->_M_ptr; }
 285
 286       // iterator support
 287
 288       constexpr iterator
 289       begin() const noexcept
 290       { return iterator(this->_M_ptr); }
 291
 292       constexpr const_iterator
 293       cbegin() const noexcept
 294       { return const_iterator(this->_M_ptr); }
 295
 296       constexpr iterator
 297       end() const noexcept
 298       { return iterator(this->_M_ptr + this->size()); }
 299
 300       constexpr const_iterator
 301       cend() const noexcept
 302       { return const_iterator(this->_M_ptr + this->size()); }
 303
 304       constexpr reverse_iterator
 305       rbegin() const noexcept
 306       { return reverse_iterator(this->end()); }
 307
 308       constexpr const_reverse_iterator
 309       crbegin() const noexcept
 310       { return const_reverse_iterator(this->cend()); }
 311
 312       constexpr reverse_iterator
 313       rend() const noexcept
 314       { return reverse_iterator(this->begin()); }
 315
 316       constexpr const_reverse_iterator
 317       crend() const noexcept
 318       { return const_reverse_iterator(this->cbegin()); }
 319
 320       // subviews
 321
 322       template<size_t _Count>
 323         constexpr span<element_type, _Count>
 324         first() const noexcept
 325         {
 326           if constexpr (_Extent == dynamic_extent)
 327             __glibcxx_assert(_Count <= size());
 328           else
 329             static_assert(_Count <= extent);
 330           return { this->data(), _Count };
 331         }
 332
 333       constexpr span<element_type, dynamic_extent>
 334       first(size_type __count) const noexcept
 335       {
 336         __glibcxx_assert(__count <= size());
 337         return { this->data(), __count };
 338       }
 339
 340       template<size_t _Count>
 341         constexpr span<element_type, _Count>
 342         last() const noexcept
 343         {
 344           if constexpr (_Extent == dynamic_extent)
 345             __glibcxx_assert(_Count <= size());
 346           else
 347             static_assert(_Count <= extent);
 348           return { this->data() + (this->size() - _Count), _Count };
 349         }
 350
 351       constexpr span<element_type, dynamic_extent>
 352       last(size_type __count) const noexcept
 353       {
 354         __glibcxx_assert(__count <= size());
 355         return { this->data() + (this->size() - __count), __count };
 356       }
 357
 358       template<size_t _Offset, size_t _Count = dynamic_extent>
 359         constexpr auto
 360         subspan() const noexcept
 361         -> span<element_type, _S_subspan_extent<_Offset, _Count>()>
 362         {
 363           if constexpr (_Extent == dynamic_extent)
 364             __glibcxx_assert(_Offset <= size());
 365           else
 366             static_assert(_Offset <= extent);
 367
 368           if constexpr (_Count == dynamic_extent)
 369             return { this->data() + _Offset, this->size() - _Offset };
 370           else
 371             {
 372               if constexpr (_Extent == dynamic_extent)
 373                 {
 374                   __glibcxx_assert(_Count <= size());
 375                   __glibcxx_assert(_Count <= (size() - _Offset));
 376                 }
 377               else
 378                 {
 379                   static_assert(_Count <= extent);
 380                   static_assert(_Count <= (extent - _Offset));
 381                 }
 382               return { this->data() + _Offset, _Count };
 383             }
 384         }
 385
 386       constexpr span<element_type, dynamic_extent>
 387       subspan(size_type __offset, size_type __count = dynamic_extent) const
 388       noexcept
 389       {
 390         __glibcxx_assert(__offset <= size());
 391         if (__count == dynamic_extent)
 392           __count = this->size() - __offset;
 393         else
 394           {
 395             __glibcxx_assert(__count <= size());
 396             __glibcxx_assert(__offset + __count <= size());
 397           }
 398         return {this->data() + __offset, __count};
 399       }
 400
 401     private:
 402       [[no_unique_address]] __detail::__extent_storage<extent> _M_extent;
 403       pointer _M_ptr;
 404     };
 405
 406   // deduction guides
 407   template<typename _Type, size_t _ArrayExtent>
 408     span(_Type(&)[_ArrayExtent]) -> span<_Type, _ArrayExtent>;
 409
 410   template<typename _Type, size_t _ArrayExtent>
 411     span(array<_Type, _ArrayExtent>&) -> span<_Type, _ArrayExtent>;
 412
 413   template<typename _Type, size_t _ArrayExtent>
 414     span(const array<_Type, _ArrayExtent>&)
 415       -> span<const _Type, _ArrayExtent>;
 416
 417   template<contiguous_iterator _Iter, typename _Sentinel>
 418     span(_Iter, _Sentinel)
 419       -> span<remove_reference_t<ranges::range_reference_t<_Iter>>>;
 420
 421   template<typename _Range>
 422     span(_Range &&)
 423       -> span<remove_reference_t<ranges::range_reference_t<_Range&>>>;
 424
 425   template<typename _Type, size_t _Extent>
 426     inline
 427     span<const byte, _Extent == dynamic_extent
 428         ? dynamic_extent : _Extent * sizeof(_Type)>
 429     as_bytes(span<_Type, _Extent> __sp) noexcept
 430     {
 431       return {reinterpret_cast<const byte*>(__sp.data()), __sp.size_bytes()};
 432     }
 433
 434   template<typename _Type, size_t _Extent>
 435     inline
 436     span<byte, _Extent == dynamic_extent
 437        ? dynamic_extent : _Extent * sizeof(_Type)>
 438     as_writable_bytes(span<_Type, _Extent> __sp) noexcept
 439     {
 440       return {reinterpret_cast<byte*>(__sp.data()), __sp.size_bytes()};
 441     }
 442
 443   // tuple helpers
 444   template<size_t _Index, typename _Type, size_t _Extent>
 445     constexpr _Type&
 446     get(span<_Type, _Extent> __sp) noexcept
 447     {
 448       static_assert(_Extent != dynamic_extent && _Index < _Extent,
 449         "get<I> can only be used with a span of non-dynamic (fixed) extent");
 450       return __sp[_Index];
 451     }
 452
 453   template<typename _Tp> struct tuple_size;
 454   template<size_t __i, typename _Tp> struct tuple_element;
 455
 456   template<typename _Type, size_t _Extent>
 457     struct tuple_size<span<_Type, _Extent>>
 458     : public integral_constant<size_t, _Extent>
 459     {
 460       static_assert(_Extent != dynamic_extent, "tuple_size can only "
 461         "be used with a span of non-dynamic (fixed) extent");
 462     };
 463
 464   template<size_t _Index, typename _Type, size_t _Extent>
 465     struct tuple_element<_Index, span<_Type, _Extent>>
 466     {
 467       static_assert(_Extent != dynamic_extent, "tuple_element can only "
 468         "be used with a span of non-dynamic (fixed) extent");
 469       static_assert(_Index < _Extent, "Index is less than Extent");
 470       using type = _Type;
 471     };
 472
 473   namespace ranges
 474   {
 475     template<typename> extern inline const bool enable_safe_range;
 476     // Opt-in to safe_range concept
 477     template<typename _ElementType, size_t _Extent>
 478       inline constexpr bool
 479         enable_safe_range<span<_ElementType, _Extent>> = true;
 480   }
 481 _GLIBCXX_END_NAMESPACE_VERSION
 482 } // namespace std
 483 #endif // concepts
 484 #endif // C++20
 485 #endif // _GLIBCXX_SPAN