text: // Copyright (C) 2017-2019 Free Software Foundation, Inc.
  //
  // This file is part of the GNU ISO C++ Library.  This library is free
  // software; you can redistribute it and/or modify it under the
  // terms of the GNU General Public License as published by the
  // Free Software Foundation; either version 3, or (at your option)
  // any later version.
  
  // This library is distributed in the hope that it will be useful,
  // but WITHOUT ANY WARRANTY; without even the implied warranty of
  // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  // GNU General Public License for more details.
  
  // You should have received a copy of the GNU General Public License along
  // with this library; see the file COPYING3.  If not see
  // <http://www.gnu.org/licenses/>.
  
  // { dg-options "-std=gnu++17" }
  // { dg-do compile { target c++17 } }
  
  #include <string_view>
  
  struct constexpr_char_traits : std::char_traits<char>
  {
    static constexpr size_t
    length(const char* val)
    {
      size_t res = 0;
      for (; val[res] != '\0'; ++res)
        ;
      return res;
    }
  
    static constexpr int
    compare(const char* lhs, const char* rhs, std::size_t count)
    {
      for (size_t pos = 0; pos < count; ++pos)
      {
        if (lhs[pos] != rhs[pos])
          return lhs[pos] - rhs[pos];
      }
      return 0;
    }
  };
  
  using string_view = std::basic_string_view<char, constexpr_char_traits>;
  
  constexpr
  string_view get()
  {
      string_view res = "x::";
      string_view start_pattern = "x";
      res = res.substr(res.find(start_pattern) + start_pattern.size());
      res = res.substr(0, res.find_first_of(";]"));
      res = res.substr(res.rfind("::"));
      return res;
  }
  
  static_assert( get() == get() );
  
  using std::u16string_view;
  
  constexpr
  u16string_view get16()
  {
      u16string_view res = u"x::";
      u16string_view start_pattern = u"x";
      res = res.substr(res.find(start_pattern) + start_pattern.size());
      res = res.substr(0, res.find_first_of(u";]"));
      res = res.substr(res.rfind(u"::"));
      return res;
  }
  
  static_assert( get16() == get16() );
  
  using std::u32string_view;
  
  constexpr
  u32string_view get32()
  {
      u32string_view res = U"x::";
      u32string_view start_pattern = U"x";
      res = res.substr(res.find(start_pattern) + start_pattern.size());
      res = res.substr(0, res.find_first_of(U";]"));
      res = res.substr(res.rfind(U"::"));
      return res;
  }
  
  static_assert( get32() == get32() );
  