xapian-core/common/output.h

   1 /** @file
   2  * @brief std::ostream operator<< template for Xapian objects
   3  */
   4 /* Copyright (C) 2016 Olly Betts
   5  *
   6  * Permission is hereby granted, free of charge, to any person obtaining a copy
   7  * of this software and associated documentation files (the "Software"), to
   8  * deal in the Software without restriction, including without limitation the
   9  * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
  10  * sell copies of the Software, and to permit persons to whom the Software is
  11  * furnished to do so, subject to the following conditions:
  12  *
  13  * The above copyright notice and this permission notice shall be included in
  14  * all copies or substantial portions of the Software.
  15  *
  16  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  17  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  18  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  19  * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  20  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
  21  * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
  22  * IN THE SOFTWARE.
  23  */
  24
  25 #ifndef XAPIAN_INCLUDED_COMMON_OUTPUT_H
  26 #define XAPIAN_INCLUDED_COMMON_OUTPUT_H
  27
  28 #include <ostream>
  29
  30 // The decltype() of a comma expression is a trick to leverage SFINAE to
  31 // provide this template for classes with a "get_description() const" method,
  32 // while providing the expected return type for the function.
  33 template<class T>
  34 auto operator<<(std::ostream& os, const T& t)
  35     -> decltype(t.get_description(), os)
  36 {
  37     return os << t.get_description();
  38 }
  39
  40 #endif