typeTraits.hpp

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/** \file typeTraits.hpp
 * \brief A collection of type trait evaluations.
 * \ingroup utils_files
 * \author Jared R. Males (jaredmales@gmail.com)
 *
 */
 
//***********************************************************************//
// Copyright 2015, 2016, 2017, 2018 Jared R. Males (jaredmales@gmail.com)
//
// This file is part of mxlib.
//
// mxlib is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// mxlib 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 for more details.
//
// You should have received a copy of the GNU General Public License
// along with mxlib.  If not, see <http://www.gnu.org/licenses/>.
//***********************************************************************//
 
#ifndef typeTraits_hpp
#define typeTraits_hpp
 
#include <type_traits>
#include <vector>
 
#include "trueFalseT.hpp"
 
namespace mx
{
 
namespace meta
{
 
template <typename... Ts>
using void_t = void;
 
template <typename T, typename = void>
struct has_value_type : trueFalseT<false>
{
};
 
/// Test whether a type has a typedef of "value_type"
/** Used for compile-time determination of type.
 *
 * Example usage:
 * \code
 * bool has_vt = has_value_type<std::vector<float> >; //Evaluates to true
 * bool has_not_vt = has_value_type<float>; //Evaluates to false
 * \endcode
 *
 * This was taken directly from the example at http://en.wikipedia.org/wiki/Substitution_failure_is_not_an_error
 *
 * \ingroup meta
 */
template <typename T>
struct has_value_type<T, void_t<typename T::value_type>> : trueFalseT<true>
{
};
 
/// Check whether a type is std::vector or not.
/** First resolves whether the type as a typedef value_type.  If not, then member value will be false.
 * If it does have a member type value_type, then it uses std::is_same to compare the type to std::vector.
 * Then value is equal to std::is_same<T, std::vector<typenameT::value_type>>::value.
 *
 * \tparam T is the type to evaulate for vector-ness.
 * \tparam has_value_type is a boolean type based on has_value_type SFINAE test.
 *
 * \ingroup meta
 */
template <typename T, bool if_value_type = has_value_type<T>::value>
struct is_std_vector;
 
/// Partial specialization for the case with value_type member type in T, invoking std::is_same.
/** \ingroup meta
 */
template <typename T>
struct is_std_vector<T, true>
{
    static const bool value = std::is_same<T, std::vector<typename T::value_type>>::value;
};
 
/// Partial specialization for the case with no value_type member type in T.
/** \ingroup meta
 */
template <typename T>
struct is_std_vector<T, false>
{
    static const bool value = false;
};
 
} // namespace meta
} // namespace mx
 
#endif // typeTraits_hpp