text: //===----------------------------------------------------------------------===//
  //
  // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
  // See https://llvm.org/LICENSE.txt for license information.
  // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
  //
  //===----------------------------------------------------------------------===//
  
  // <string>
  
  // template<class charT, class traits, class Allocator>
  //   basic_ostream<charT, traits>&
  //   operator<<(basic_ostream<charT, traits>& os,
  //              const basic_string_view<charT,traits> str);
  
  #include <string_view>
  #include <iosfwd>
  
  template <class SV, class = void>
  struct HasDecl : std::false_type {};
  template <class SV>
  struct HasDecl<SV, decltype(static_cast<void>(std::declval<std::ostream&>() << std::declval<SV&>()))> : std::true_type {};
  
  int main() {
    static_assert(HasDecl<std::string_view>::value, "streaming operator declaration not present");
  }
  