Option.hpp

/* Copyright 2020-2021 Franz Poeschel
 *
 * This file is part of openPMD-api.
 *
 * openPMD-api is free software: you can redistribute it and/or modify
 * it under the terms of of either the GNU General Public License or
 * the GNU Lesser General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * openPMD-api is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License and the GNU Lesser General Public License
 * for more details.
 *
 * You should have received a copy of the GNU General Public License
 * and the GNU Lesser General Public License along with openPMD-api.
 * If not, see <http://www.gnu.org/licenses/>.
 */
 
#pragma once
 
#include "VariantSrc.hpp"
 
#include <utility> // std::forward, std::move
#include <type_traits>
 
 
namespace openPMD
{
namespace auxiliary
{
    namespace detail
    {
        struct Empty
        {
        };
    } // namespace detail
 
    template< typename T >
    class Option
    {
        using data_t = variantSrc::variant< T, detail::Empty >;
        data_t m_data;
 
    public:
        explicit Option() : m_data( detail::Empty() )
        {
        }
 
        Option( T data ) : m_data( std::move( data ) )
        {
        }
 
        Option( Option const & other ) = default;
 
        Option &
        operator=( Option && other )
        {
            if( other.has_value() )
            {
                m_data.template emplace< 0 >( std::move( other.get() ) );
            }
            else
            {
                m_data.template emplace< 1 >( detail::Empty() );
            }
            return *this;
        }
 
        Option &
        operator=( Option const & other )
        {
            if( other.has_value() )
            {
                m_data.template emplace< 0 >( other.get() );
            }
            else
            {
                m_data.template emplace< 1 >( detail::Empty() );
            }
            return *this;
        }
 
        bool
        operator==( Option const & other ) const
        {
            if( has_value() )
            {
                return !other.has_value();
            }
            else
            {
                if( !other.has_value() )
                {
                    return false;
                }
                else
                {
                    return get() == other.get();
                }
            }
        }
 
        bool
        operator!=( Option const & other ) const
        {
            return !( *this == other );
        }
 
        bool
        has_value() const
        {
            return m_data.index() == 0;
        }
 
        operator bool() const
        {
            return has_value();
        }
 
        T const &
        get() const
        {
            return variantSrc::template get< T >( m_data );
        }
 
        T &
        get()
        {
            return variantSrc::template get< T >( m_data );
        }
    };
 
    template< typename T >
    Option< typename std::decay< T >::type >
    makeOption( T && val )
    {
        return Option< typename std::decay< T >::type >(
            std::forward< T >( val ) );
    }
} // namespace auxiliary
} // namespace openPMD