is_defined.h

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/* +------------------------------------------------------------------------+
   |                     Mobile Robot Programming Toolkit (MRPT)            |
   |                          https://www.mrpt.org/                         |
   |                                                                        |
   | Copyright (c) 2005-2019, Individual contributors, see AUTHORS file     |
   | See: https://www.mrpt.org/Authors - All rights reserved.               |
   | Released under BSD License. See: https://www.mrpt.org/License          |
   +------------------------------------------------------------------------+ */
#pragma once

#include <type_traits>  // enable_if_t

namespace mrpt
{
/** Checks if type is defined (fails for forward declarations).
 * \note Credits: WindyFields https://stackoverflow.com/a/45594334/1631514
 */
template <class T, class Enable = void>
struct is_defined
{
    static constexpr bool value = false;
};
template <class T>
struct is_defined<T, std::enable_if_t<(sizeof(T) > 0)>>
{
    static constexpr bool value = true;
};

template <class T>
inline constexpr bool is_defined_v = is_defined<T>::value;

}  // namespace mrpt