libstdc++-v3/include/std/string_view

   1 // Components for manipulating non-owning sequences of characters -*- C++ -*-
   2
   3 // Copyright (C) 2013-2019 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 string_view
  26  *  This is a Standard C++ Library header.
  27  */
  28
  29 //
  30 // N3762 basic_string_view library
  31 //
  32
  33 #ifndef _GLIBCXX_STRING_VIEW
  34 #define _GLIBCXX_STRING_VIEW 1
  35
  36 #pragma GCC system_header
  37
  38 #if __cplusplus >= 201703L
  39
  40 #include <limits>
  41 #include <iosfwd>
  42 #include <bits/char_traits.h>
  43 #include <bits/functional_hash.h>
  44 #include <bits/range_access.h>
  45
  46 namespace std _GLIBCXX_VISIBILITY(default)
  47 {
  48 _GLIBCXX_BEGIN_NAMESPACE_VERSION
  49
  50 #define __cpp_lib_string_view 201603
  51
  52   /**
  53    *  @class basic_string_view <string_view>
  54    *  @brief  A non-owning reference to a string.
  55    *
  56    *  @ingroup strings
  57    *  @ingroup sequences
  58    *
  59    *  @tparam _CharT  Type of character
  60    *  @tparam _Traits  Traits for character type, defaults to
  61    *                   char_traits<_CharT>.
  62    *
  63    *  A basic_string_view looks like this:
  64    *
  65    *  @code
  66    *    _CharT*    _M_str
  67    *    size_t     _M_len
  68    *  @endcode
  69    */
  70   template<typename _CharT, typename _Traits = std::char_traits<_CharT>>
  71     class basic_string_view
  72     {
  73     public:
  74
  75       // types
  76       using traits_type = _Traits;
  77       using value_type = _CharT;
  78       using pointer = const _CharT*;
  79       using const_pointer = const _CharT*;
  80       using reference = const _CharT&;
  81       using const_reference = const _CharT&;
  82       using const_iterator = const _CharT*;
  83       using iterator = const_iterator;
  84       using const_reverse_iterator = std::reverse_iterator<const_iterator>;
  85       using reverse_iterator = const_reverse_iterator;
  86       using size_type = size_t;
  87       using difference_type = ptrdiff_t;
  88       static constexpr size_type npos = size_type(-1);
  89
  90       // [string.view.cons], construct/copy
  91
  92       constexpr
  93       basic_string_view() noexcept
  94       : _M_len{0}, _M_str{nullptr}
  95       { }
  96
  97       constexpr basic_string_view(const basic_string_view&) noexcept = default;
  98
  99       __attribute__((__nonnull__)) constexpr
 100       basic_string_view(const _CharT* __str) noexcept
 101       : _M_len{traits_type::length(__str)},
 102         _M_str{__str}
 103       { }
 104
 105       constexpr
 106       basic_string_view(const _CharT* __str, size_type __len) noexcept
 107       : _M_len{__len}, _M_str{__str}
 108       { }
 109
 110       constexpr basic_string_view&
 111       operator=(const basic_string_view&) noexcept = default;
 112
 113       // [string.view.iterators], iterators
 114
 115       constexpr const_iterator
 116       begin() const noexcept
 117       { return this->_M_str; }
 118
 119       constexpr const_iterator
 120       end() const noexcept
 121       { return this->_M_str + this->_M_len; }
 122
 123       constexpr const_iterator
 124       cbegin() const noexcept
 125       { return this->_M_str; }
 126
 127       constexpr const_iterator
 128       cend() const noexcept
 129       { return this->_M_str + this->_M_len; }
 130
 131       constexpr const_reverse_iterator
 132       rbegin() const noexcept
 133       { return const_reverse_iterator(this->end()); }
 134
 135       constexpr const_reverse_iterator
 136       rend() const noexcept
 137       { return const_reverse_iterator(this->begin()); }
 138
 139       constexpr const_reverse_iterator
 140       crbegin() const noexcept
 141       { return const_reverse_iterator(this->end()); }
 142
 143       constexpr const_reverse_iterator
 144       crend() const noexcept
 145       { return const_reverse_iterator(this->begin()); }
 146
 147       // [string.view.capacity], capacity
 148
 149       constexpr size_type
 150       size() const noexcept
 151       { return this->_M_len; }
 152
 153       constexpr size_type
 154       length() const noexcept
 155       { return _M_len; }
 156
 157       constexpr size_type
 158       max_size() const noexcept
 159       {
 160         return (npos - sizeof(size_type) - sizeof(void*))
 161                 / sizeof(value_type) / 4;
 162       }
 163
 164       [[nodiscard]] constexpr bool
 165       empty() const noexcept
 166       { return this->_M_len == 0; }
 167
 168       // [string.view.access], element access
 169
 170       constexpr const _CharT&
 171       operator[](size_type __pos) const noexcept
 172       {
 173         // TODO: Assert to restore in a way compatible with the constexpr.
 174         // __glibcxx_assert(__pos < this->_M_len);
 175         return *(this->_M_str + __pos);
 176       }
 177
 178       constexpr const _CharT&
 179       at(size_type __pos) const
 180       {
 181         if (__pos >= _M_len)
 182           __throw_out_of_range_fmt(__N("basic_string_view::at: __pos "
 183                                        "(which is %zu) >= this->size() "
 184                                        "(which is %zu)"), __pos, this->size());
 185         return *(this->_M_str + __pos);
 186       }
 187
 188       constexpr const _CharT&
 189       front() const noexcept
 190       {
 191         // TODO: Assert to restore in a way compatible with the constexpr.
 192         // __glibcxx_assert(this->_M_len > 0);
 193         return *this->_M_str;
 194       }
 195
 196       constexpr const _CharT&
 197       back() const noexcept
 198       {
 199         // TODO: Assert to restore in a way compatible with the constexpr.
 200         // __glibcxx_assert(this->_M_len > 0);
 201         return *(this->_M_str + this->_M_len - 1);
 202       }
 203
 204       constexpr const _CharT*
 205       data() const noexcept
 206       { return this->_M_str; }
 207
 208       // [string.view.modifiers], modifiers:
 209
 210       constexpr void
 211       remove_prefix(size_type __n) noexcept
 212       {
 213         __glibcxx_assert(this->_M_len >= __n);
 214         this->_M_str += __n;
 215         this->_M_len -= __n;
 216       }
 217
 218       constexpr void
 219       remove_suffix(size_type __n) noexcept
 220       { this->_M_len -= __n; }
 221
 222       constexpr void
 223       swap(basic_string_view& __sv) noexcept
 224       {
 225         auto __tmp = *this;
 226         *this = __sv;
 227         __sv = __tmp;
 228       }
 229
 230       // [string.view.ops], string operations:
 231
 232       size_type
 233       copy(_CharT* __str, size_type __n, size_type __pos = 0) const
 234       {
 235         __glibcxx_requires_string_len(__str, __n);
 236         __pos = _M_check(__pos, "basic_string_view::copy");
 237         const size_type __rlen = std::min(__n, _M_len - __pos);
 238         // _GLIBCXX_RESOLVE_LIB_DEFECTS
 239         // 2777. basic_string_view::copy should use char_traits::copy
 240         traits_type::copy(__str, data() + __pos, __rlen);
 241         return __rlen;
 242       }
 243
 244       constexpr basic_string_view
 245       substr(size_type __pos = 0, size_type __n = npos) const noexcept(false)
 246       {
 247         __pos = _M_check(__pos, "basic_string_view::substr");
 248         const size_type __rlen = std::min(__n, _M_len - __pos);
 249         return basic_string_view{_M_str + __pos, __rlen};
 250       }
 251
 252       constexpr int
 253       compare(basic_string_view __str) const noexcept
 254       {
 255         const size_type __rlen = std::min(this->_M_len, __str._M_len);
 256         int __ret = traits_type::compare(this->_M_str, __str._M_str, __rlen);
 257         if (__ret == 0)
 258           __ret = _S_compare(this->_M_len, __str._M_len);
 259         return __ret;
 260       }
 261
 262       constexpr int
 263       compare(size_type __pos1, size_type __n1, basic_string_view __str) const
 264       { return this->substr(__pos1, __n1).compare(__str); }
 265
 266       constexpr int
 267       compare(size_type __pos1, size_type __n1,
 268               basic_string_view __str, size_type __pos2, size_type __n2) const
 269       {
 270         return this->substr(__pos1, __n1).compare(__str.substr(__pos2, __n2));
 271       }
 272
 273       __attribute__((__nonnull__)) constexpr int
 274       compare(const _CharT* __str) const noexcept
 275       { return this->compare(basic_string_view{__str}); }
 276
 277       __attribute__((__nonnull__)) constexpr int
 278       compare(size_type __pos1, size_type __n1, const _CharT* __str) const
 279       { return this->substr(__pos1, __n1).compare(basic_string_view{__str}); }
 280
 281       constexpr int
 282       compare(size_type __pos1, size_type __n1,
 283               const _CharT* __str, size_type __n2) const noexcept(false)
 284       {
 285         return this->substr(__pos1, __n1)
 286                    .compare(basic_string_view(__str, __n2));
 287       }
 288
 289       constexpr size_type
 290       find(basic_string_view __str, size_type __pos = 0) const noexcept
 291       { return this->find(__str._M_str, __pos, __str._M_len); }
 292
 293       constexpr size_type
 294       find(_CharT __c, size_type __pos = 0) const noexcept;
 295
 296       constexpr size_type
 297       find(const _CharT* __str, size_type __pos, size_type __n) const noexcept;
 298
 299       __attribute__((__nonnull__)) constexpr size_type
 300       find(const _CharT* __str, size_type __pos = 0) const noexcept
 301       { return this->find(__str, __pos, traits_type::length(__str)); }
 302
 303       constexpr size_type
 304       rfind(basic_string_view __str, size_type __pos = npos) const noexcept
 305       { return this->rfind(__str._M_str, __pos, __str._M_len); }
 306
 307       constexpr size_type
 308       rfind(_CharT __c, size_type __pos = npos) const noexcept;
 309
 310       constexpr size_type
 311       rfind(const _CharT* __str, size_type __pos, size_type __n) const noexcept;
 312
 313       __attribute__((__nonnull__)) constexpr size_type
 314       rfind(const _CharT* __str, size_type __pos = npos) const noexcept
 315       { return this->rfind(__str, __pos, traits_type::length(__str)); }
 316
 317       constexpr size_type
 318       find_first_of(basic_string_view __str, size_type __pos = 0) const noexcept
 319       { return this->find_first_of(__str._M_str, __pos, __str._M_len); }
 320
 321       constexpr size_type
 322       find_first_of(_CharT __c, size_type __pos = 0) const noexcept
 323       { return this->find(__c, __pos); }
 324
 325       constexpr size_type
 326       find_first_of(const _CharT* __str, size_type __pos,
 327                     size_type __n) const noexcept;
 328
 329       __attribute__((__nonnull__)) constexpr size_type
 330       find_first_of(const _CharT* __str, size_type __pos = 0) const noexcept
 331       { return this->find_first_of(__str, __pos, traits_type::length(__str)); }
 332
 333       constexpr size_type
 334       find_last_of(basic_string_view __str,
 335                    size_type __pos = npos) const noexcept
 336       { return this->find_last_of(__str._M_str, __pos, __str._M_len); }
 337
 338       constexpr size_type
 339       find_last_of(_CharT __c, size_type __pos=npos) const noexcept
 340       { return this->rfind(__c, __pos); }
 341
 342       constexpr size_type
 343       find_last_of(const _CharT* __str, size_type __pos,
 344                    size_type __n) const noexcept;
 345
 346       __attribute__((__nonnull__)) constexpr size_type
 347       find_last_of(const _CharT* __str, size_type __pos = npos) const noexcept
 348       { return this->find_last_of(__str, __pos, traits_type::length(__str)); }
 349
 350       constexpr size_type
 351       find_first_not_of(basic_string_view __str,
 352                         size_type __pos = 0) const noexcept
 353       { return this->find_first_not_of(__str._M_str, __pos, __str._M_len); }
 354
 355       constexpr size_type
 356       find_first_not_of(_CharT __c, size_type __pos = 0) const noexcept;
 357
 358       constexpr size_type
 359       find_first_not_of(const _CharT* __str,
 360                         size_type __pos, size_type __n) const noexcept;
 361
 362       __attribute__((__nonnull__)) constexpr size_type
 363       find_first_not_of(const _CharT* __str, size_type __pos = 0) const noexcept
 364       {
 365         return this->find_first_not_of(__str, __pos,
 366                                        traits_type::length(__str));
 367       }
 368
 369       constexpr size_type
 370       find_last_not_of(basic_string_view __str,
 371                        size_type __pos = npos) const noexcept
 372       { return this->find_last_not_of(__str._M_str, __pos, __str._M_len); }
 373
 374       constexpr size_type
 375       find_last_not_of(_CharT __c, size_type __pos = npos) const noexcept;
 376
 377       constexpr size_type
 378       find_last_not_of(const _CharT* __str,
 379                        size_type __pos, size_type __n) const noexcept;
 380
 381       __attribute__((__nonnull__)) constexpr size_type
 382       find_last_not_of(const _CharT* __str,
 383                        size_type __pos = npos) const noexcept
 384       {
 385         return this->find_last_not_of(__str, __pos,
 386                                       traits_type::length(__str));
 387       }
 388
 389 #if __cplusplus > 201703L
 390       constexpr bool
 391       starts_with(basic_string_view __x) const noexcept
 392       { return this->substr(0, __x.size()) == __x; }
 393
 394       constexpr bool
 395       starts_with(_CharT __x) const noexcept
 396       { return !this->empty() && traits_type::eq(this->front(), __x); }
 397
 398       constexpr bool
 399       starts_with(const _CharT* __x) const noexcept
 400       { return this->starts_with(basic_string_view(__x)); }
 401
 402       constexpr bool
 403       ends_with(basic_string_view __x) const noexcept
 404       {
 405         return this->size() >= __x.size()
 406             && this->compare(this->size() - __x.size(), npos, __x) == 0;
 407       }
 408
 409       constexpr bool
 410       ends_with(_CharT __x) const noexcept
 411       { return !this->empty() && traits_type::eq(this->back(), __x); }
 412
 413       constexpr bool
 414       ends_with(const _CharT* __x) const noexcept
 415       { return this->ends_with(basic_string_view(__x)); }
 416 #endif // C++20
 417
 418       constexpr size_type
 419       _M_check(size_type __pos, const char* __s) const noexcept(false)
 420       {
 421         if (__pos > this->size())
 422           __throw_out_of_range_fmt(__N("%s: __pos (which is %zu) > "
 423                                        "this->size() (which is %zu)"),
 424                                    __s, __pos, this->size());
 425         return __pos;
 426       }
 427
 428       // NB: _M_limit doesn't check for a bad __pos value.
 429       constexpr size_type
 430       _M_limit(size_type __pos, size_type __off) const noexcept
 431       {
 432         const bool __testoff =  __off < this->size() - __pos;
 433         return __testoff ? __off : this->size() - __pos;
 434       }
 435
 436     private:
 437
 438       static constexpr int
 439       _S_compare(size_type __n1, size_type __n2) noexcept
 440       {
 441         const difference_type __diff = __n1 - __n2;
 442         if (__diff > std::numeric_limits<int>::max())
 443           return std::numeric_limits<int>::max();
 444         if (__diff < std::numeric_limits<int>::min())
 445           return std::numeric_limits<int>::min();
 446         return static_cast<int>(__diff);
 447       }
 448
 449       size_t        _M_len;
 450       const _CharT* _M_str;
 451     };
 452
 453   // [string.view.comparison], non-member basic_string_view comparison function
 454
 455   namespace __detail
 456   {
 457     // Identity transform to create a non-deduced context, so that only one
 458     // argument participates in template argument deduction and the other
 459     // argument gets implicitly converted to the deduced type. See n3766.html.
 460     template<typename _Tp>
 461       using __idt = common_type_t<_Tp>;
 462   }
 463
 464   template<typename _CharT, typename _Traits>
 465     constexpr bool
 466     operator==(basic_string_view<_CharT, _Traits> __x,
 467                basic_string_view<_CharT, _Traits> __y) noexcept
 468     { return __x.size() == __y.size() && __x.compare(__y) == 0; }
 469
 470   template<typename _CharT, typename _Traits>
 471     constexpr bool
 472     operator==(basic_string_view<_CharT, _Traits> __x,
 473                __detail::__idt<basic_string_view<_CharT, _Traits>> __y) noexcept
 474     { return __x.size() == __y.size() && __x.compare(__y) == 0; }
 475
 476   template<typename _CharT, typename _Traits>
 477     constexpr bool
 478     operator==(__detail::__idt<basic_string_view<_CharT, _Traits>> __x,
 479                basic_string_view<_CharT, _Traits> __y) noexcept
 480     { return __x.size() == __y.size() && __x.compare(__y) == 0; }
 481
 482   template<typename _CharT, typename _Traits>
 483     constexpr bool
 484     operator!=(basic_string_view<_CharT, _Traits> __x,
 485                basic_string_view<_CharT, _Traits> __y) noexcept
 486     { return !(__x == __y); }
 487
 488   template<typename _CharT, typename _Traits>
 489     constexpr bool
 490     operator!=(basic_string_view<_CharT, _Traits> __x,
 491                __detail::__idt<basic_string_view<_CharT, _Traits>> __y) noexcept
 492     { return !(__x == __y); }
 493
 494   template<typename _CharT, typename _Traits>
 495     constexpr bool
 496     operator!=(__detail::__idt<basic_string_view<_CharT, _Traits>> __x,
 497                basic_string_view<_CharT, _Traits> __y) noexcept
 498     { return !(__x == __y); }
 499
 500   template<typename _CharT, typename _Traits>
 501     constexpr bool
 502     operator< (basic_string_view<_CharT, _Traits> __x,
 503                basic_string_view<_CharT, _Traits> __y) noexcept
 504     { return __x.compare(__y) < 0; }
 505
 506   template<typename _CharT, typename _Traits>
 507     constexpr bool
 508     operator< (basic_string_view<_CharT, _Traits> __x,
 509                __detail::__idt<basic_string_view<_CharT, _Traits>> __y) noexcept
 510     { return __x.compare(__y) < 0; }
 511
 512   template<typename _CharT, typename _Traits>
 513     constexpr bool
 514     operator< (__detail::__idt<basic_string_view<_CharT, _Traits>> __x,
 515                basic_string_view<_CharT, _Traits> __y) noexcept
 516     { return __x.compare(__y) < 0; }
 517
 518   template<typename _CharT, typename _Traits>
 519     constexpr bool
 520     operator> (basic_string_view<_CharT, _Traits> __x,
 521                basic_string_view<_CharT, _Traits> __y) noexcept
 522     { return __x.compare(__y) > 0; }
 523
 524   template<typename _CharT, typename _Traits>
 525     constexpr bool
 526     operator> (basic_string_view<_CharT, _Traits> __x,
 527                __detail::__idt<basic_string_view<_CharT, _Traits>> __y) noexcept
 528     { return __x.compare(__y) > 0; }
 529
 530   template<typename _CharT, typename _Traits>
 531     constexpr bool
 532     operator> (__detail::__idt<basic_string_view<_CharT, _Traits>> __x,
 533                basic_string_view<_CharT, _Traits> __y) noexcept
 534     { return __x.compare(__y) > 0; }
 535
 536   template<typename _CharT, typename _Traits>
 537     constexpr bool
 538     operator<=(basic_string_view<_CharT, _Traits> __x,
 539                basic_string_view<_CharT, _Traits> __y) noexcept
 540     { return __x.compare(__y) <= 0; }
 541
 542   template<typename _CharT, typename _Traits>
 543     constexpr bool
 544     operator<=(basic_string_view<_CharT, _Traits> __x,
 545                __detail::__idt<basic_string_view<_CharT, _Traits>> __y) noexcept
 546     { return __x.compare(__y) <= 0; }
 547
 548   template<typename _CharT, typename _Traits>
 549     constexpr bool
 550     operator<=(__detail::__idt<basic_string_view<_CharT, _Traits>> __x,
 551                basic_string_view<_CharT, _Traits> __y) noexcept
 552     { return __x.compare(__y) <= 0; }
 553
 554   template<typename _CharT, typename _Traits>
 555     constexpr bool
 556     operator>=(basic_string_view<_CharT, _Traits> __x,
 557                basic_string_view<_CharT, _Traits> __y) noexcept
 558     { return __x.compare(__y) >= 0; }
 559
 560   template<typename _CharT, typename _Traits>
 561     constexpr bool
 562     operator>=(basic_string_view<_CharT, _Traits> __x,
 563                __detail::__idt<basic_string_view<_CharT, _Traits>> __y) noexcept
 564     { return __x.compare(__y) >= 0; }
 565
 566   template<typename _CharT, typename _Traits>
 567     constexpr bool
 568     operator>=(__detail::__idt<basic_string_view<_CharT, _Traits>> __x,
 569                basic_string_view<_CharT, _Traits> __y) noexcept
 570     { return __x.compare(__y) >= 0; }
 571
 572   // [string.view.io], Inserters and extractors
 573   template<typename _CharT, typename _Traits>
 574     inline basic_ostream<_CharT, _Traits>&
 575     operator<<(basic_ostream<_CharT, _Traits>& __os,
 576                basic_string_view<_CharT,_Traits> __str)
 577     { return __ostream_insert(__os, __str.data(), __str.size()); }
 578
 579
 580   // basic_string_view typedef names
 581
 582   using string_view = basic_string_view<char>;
 583 #ifdef _GLIBCXX_USE_WCHAR_T
 584   using wstring_view = basic_string_view<wchar_t>;
 585 #endif
 586 #ifdef _GLIBCXX_USE_CHAR8_T
 587   using u8string_view = basic_string_view<char8_t>;
 588 #endif
 589   using u16string_view = basic_string_view<char16_t>;
 590   using u32string_view = basic_string_view<char32_t>;
 591
 592   // [string.view.hash], hash support:
 593
 594   template<typename _Tp>
 595     struct hash;
 596
 597   template<>
 598     struct hash<string_view>
 599     : public __hash_base<size_t, string_view>
 600     {
 601       size_t
 602       operator()(const string_view& __str) const noexcept
 603       { return std::_Hash_impl::hash(__str.data(), __str.length()); }
 604     };
 605
 606   template<>
 607     struct __is_fast_hash<hash<string_view>> : std::false_type
 608     { };
 609
 610 #ifdef _GLIBCXX_USE_WCHAR_T
 611   template<>
 612     struct hash<wstring_view>
 613     : public __hash_base<size_t, wstring>
 614     {
 615       size_t
 616       operator()(const wstring_view& __s) const noexcept
 617       { return std::_Hash_impl::hash(__s.data(),
 618                                      __s.length() * sizeof(wchar_t)); }
 619     };
 620
 621   template<>
 622     struct __is_fast_hash<hash<wstring_view>> : std::false_type
 623     { };
 624 #endif
 625
 626 #ifdef _GLIBCXX_USE_CHAR8_T
 627   template<>
 628     struct hash<u8string_view>
 629     : public __hash_base<size_t, u8string_view>
 630     {
 631       size_t
 632       operator()(const u8string_view& __str) const noexcept
 633       { return std::_Hash_impl::hash(__str.data(), __str.length()); }
 634     };
 635
 636   template<>
 637     struct __is_fast_hash<hash<u8string_view>> : std::false_type
 638     { };
 639 #endif
 640
 641   template<>
 642     struct hash<u16string_view>
 643     : public __hash_base<size_t, u16string_view>
 644     {
 645       size_t
 646       operator()(const u16string_view& __s) const noexcept
 647       { return std::_Hash_impl::hash(__s.data(),
 648                                      __s.length() * sizeof(char16_t)); }
 649     };
 650
 651   template<>
 652     struct __is_fast_hash<hash<u16string_view>> : std::false_type
 653     { };
 654
 655   template<>
 656     struct hash<u32string_view>
 657     : public __hash_base<size_t, u32string_view>
 658     {
 659       size_t
 660       operator()(const u32string_view& __s) const noexcept
 661       { return std::_Hash_impl::hash(__s.data(),
 662                                      __s.length() * sizeof(char32_t)); }
 663     };
 664
 665   template<>
 666     struct __is_fast_hash<hash<u32string_view>> : std::false_type
 667     { };
 668
 669   inline namespace literals
 670   {
 671   inline namespace string_view_literals
 672   {
 673 #pragma GCC diagnostic push
 674 #pragma GCC diagnostic ignored "-Wliteral-suffix"
 675     inline constexpr basic_string_view<char>
 676     operator""sv(const char* __str, size_t __len) noexcept
 677     { return basic_string_view<char>{__str, __len}; }
 678
 679 #ifdef _GLIBCXX_USE_WCHAR_T
 680     inline constexpr basic_string_view<wchar_t>
 681     operator""sv(const wchar_t* __str, size_t __len) noexcept
 682     { return basic_string_view<wchar_t>{__str, __len}; }
 683 #endif
 684
 685 #ifdef _GLIBCXX_USE_CHAR8_T
 686     inline constexpr basic_string_view<char8_t>
 687     operator""sv(const char8_t* __str, size_t __len) noexcept
 688     { return basic_string_view<char8_t>{__str, __len}; }
 689 #endif
 690
 691     inline constexpr basic_string_view<char16_t>
 692     operator""sv(const char16_t* __str, size_t __len) noexcept
 693     { return basic_string_view<char16_t>{__str, __len}; }
 694
 695     inline constexpr basic_string_view<char32_t>
 696     operator""sv(const char32_t* __str, size_t __len) noexcept
 697     { return basic_string_view<char32_t>{__str, __len}; }
 698
 699 #pragma GCC diagnostic pop
 700   } // namespace string_literals
 701   } // namespace literals
 702
 703 _GLIBCXX_END_NAMESPACE_VERSION
 704 } // namespace std
 705
 706 #include <bits/string_view.tcc>
 707
 708 #endif // __cplusplus <= 201402L
 709
 710 #endif // _GLIBCXX_EXPERIMENTAL_STRING_VIEW