Distribution.hpp

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//
// Thor C++ Library
// Copyright (c) 2011-2016 Jan Haller
//
// This software is provided 'as-is', without any express or implied
// warranty. In no event will the authors be held liable for any damages
// arising from the use of this software.
//
// Permission is granted to anyone to use this software for any purpose,
// including commercial applications, and to alter it and redistribute it
// freely, subject to the following restrictions:
//
// 1. The origin of this software must not be misrepresented; you must not
//    claim that you wrote the original software. If you use this software
//    in a product, an acknowledgment in the product documentation would be
//    appreciated but is not required.
//
// 2. Altered source versions must be plainly marked as such, and must not be
//    misrepresented as being the original software.
//
// 3. This notice may not be removed or altered from any source distribution.
//


#ifndef THOR_DISTRIBUTION_HPP
#define THOR_DISTRIBUTION_HPP

#include <Aurora/Meta/Templates.hpp>

#include <functional>
#include <type_traits>


namespace thor
{

template <typename T>
class Distribution;

namespace detail
{

    // Functor that returns always the same value (don't use lambda expression because of Clang compiler bug)
    template <typename T>
    struct Constant
    {
        explicit Constant(T value)
        : value(value)
        {
        }

        T operator() () const
        {
            return value;
        }

        T value;
    };

    // Metafunction for SFINAE and reasonable compiler errors
    template <typename Fn, typename T>
    struct IsCompatibleFunction
    {
        // General case: Fn is a functor/function -> if it's not convertible to T (and thus not a constant), accept it
        static const bool value = !std::is_convertible<Fn, T>::value;
    };

    template <typename U, typename T>
    struct IsCompatibleFunction<Distribution<U>, T>
    {
        // If Fn is another Distribution<U>, accept it iff U is convertible to T (like all functors, but clearer error message)
        static const bool value = std::is_convertible<U, T>::value;
    };

} // namespace detail

// ---------------------------------------------------------------------------------------------------------------------------



template <typename T>
class Distribution
{
    // ---------------------------------------------------------------------------------------------------------------------------
    // Private types
    private:
        typedef std::function<T()> FactoryFn;


    // ---------------------------------------------------------------------------------------------------------------------------
    // Public member functions
    public:
        template <typename U>
                                    Distribution(U constant
                                        AURORA_ENABLE_IF(std::is_convertible<U, T>::value))
        : mFactory(detail::Constant<T>(constant))
        {
        }

        template <typename Fn>
                                    Distribution(Fn function
                                        AURORA_ENABLE_IF(detail::IsCompatibleFunction<Fn, T>::value))
        : mFactory(function)
        {
        }

        T                           operator() () const
        {
            return mFactory();
        }


    // ---------------------------------------------------------------------------------------------------------------------------
    // Private variables
    private:
        FactoryFn                   mFactory;
};


} // namespace thor

#endif // THOR_DISTRIBUTION_HPP