magnum/src/Magnum/Math/StrictWeakOrdering.h

#ifndef Magnum_Math_StrictWeakOrdering_h
#define Magnum_Math_StrictWeakOrdering_h
/*
    This file is part of Magnum.

    Copyright © 2010, 2011, 2012, 2013, 2014, 2015, 2016, 2017, 2018
              Vladimír Vondruš <mosra@centrum.cz>

    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.
*/

/** @file
 * @brief Class @ref Magnum::Math::StrictWeakOrdering
 */

namespace Magnum { namespace Math {

namespace Implementation {

template<class T> struct StrictWeakOrdering { /* Specialized for supported types */
    bool operator()(const T& a, const T& b) const {
        return a < b;
    }
};

}

/**
@brief A functor which implements strict weak ordering for all types in the Math library.

A strict weak ordering enables a comparison operator between to elements of a
set. With it an ordering can be achieved between the elements.

This is useful mainly for interoperability with ordering containers from the
C++ standard library, like @ref std::map and @ref std::set.

@snippet MagnumMath.cpp StrictWeakOrdering

Check the source for defails if you want to create an implementation for your
own types.
 */
struct StrictWeakOrdering {
    /**
     * @brief Compares two items.
     *
     * Returns true if a is less than b.
     *
     * Returns false if a is equivalent to b or greater.
     *
     * For scalar types this is equivalent to operator <
     */
    template<class T> bool operator()(const T& a, const T& b) const {
        /* Instantiate a specialization of Implementation::StrictWeakOrdering.
           If users want to enable this for their own types, they must create
           a specialization of Magnum::Math::Implementation::StrictWeakOrdering
           for them. */
        Implementation::StrictWeakOrdering<T> o;
        return o(a, b);
    }
};

}}

#endif