output.h

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/* Copyright (C) 2016 Olly Betts
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to
 * deal in the Software without restriction, including without limitation the
 * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
 * sell copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
 * IN THE SOFTWARE.
 */
 
#ifndef XAPIAN_INCLUDED_COMMON_OUTPUT_H
#define XAPIAN_INCLUDED_COMMON_OUTPUT_H
 
#include <ostream>
 
// The decltype() of a comma expression is a trick to leverage SFINAE to
// provide this template for classes with a "get_description() const" method,
// while providing the expected return type for the function.
template<class T>
auto operator<<(std::ostream& os, const T& t)
    -> decltype(t.get_description(), os)
{
    return os << t.get_description();
}
 
#endif