DefaultValue.hpp

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/*
 * ------------------------------------------------------------------------------------------------------------
 * SPDX-License-Identifier: LGPL-2.1-only
 *
 * Copyright (c) 2018-2020 Lawrence Livermore National Security LLC
 * Copyright (c) 2018-2020 The Board of Trustees of the Leland Stanford Junior University
 * Copyright (c) 2018-2020 Total, S.A
 * Copyright (c) 2019-     GEOSX Contributors
 * All rights reserved
 *
 * See top level LICENSE, COPYRIGHT, CONTRIBUTORS, NOTICE, and ACKNOWLEDGEMENTS files for details.
 * ------------------------------------------------------------------------------------------------------------
 */

#ifndef GEOSX_DATAREPOSITORY_DEFAULTVALUE_HPP_
#define GEOSX_DATAREPOSITORY_DEFAULTVALUE_HPP_

// Source includes
#include "common/DataTypes.hpp"
#include "codingUtilities/traits.hpp"

namespace geosx
{
namespace dataRepository
{
namespace internal
{

template< typename T >
struct is_defaultable
{
  static constexpr bool value = std::is_arithmetic< T > ::value ||
                                std::is_same< T, string >::value ||
                                std::is_same< T, Path >::value ||
                                traits::is_tensorT< T > ||
                                std::is_enum< T >::value;
};

template< typename T, typename ENABLE=void >
struct Helper
{
  static constexpr bool has_default_value = false;

  using value_type = void;
};

template< typename T >
struct Helper< T, std::enable_if_t< is_defaultable< T >::value > >
{
  static constexpr bool has_default_value = true;

  using value_type = T;

  value_type value = value_type();
};

template< typename T >
struct Helper< T, std::enable_if_t< traits::HasAlias_value_type< T > &&
                                    is_defaultable< typename T::value_type >::value &&
                                    !traits::is_string< T > &&
                                    !traits::is_tensorT< T > > >
{
  static constexpr bool has_default_value = true;

  using value_type = typename T::value_type;

  value_type value = value_type();
};

template< typename T >
std::enable_if_t< !Helper< T >::has_default_value, std::ostream & >
operator<<( std::ostream & stream, Helper< T > const & GEOSX_UNUSED_PARAM( value ) )
{
  return stream;
}

template< typename T >
std::enable_if_t< Helper< T >::has_default_value, std::ostream & >
operator<<( std::ostream & stream, Helper< T > const & value )
{
  return stream << value.value;
}

} // namespace internal

template< typename T >
using DefaultValue = internal::Helper< T >;

} // namespace dataRepository
} // namespace geosx


#endif /* GEOSX_DATAREPOSITORY_DEFAULTVALUE_HPP_ */