Added type trait for copying const qualifier.

    static constexpr bool value = ( sizeof( test< std::decay_t<T> >(0) ) == sizeof( YesType ) );

};

/**

 * \brief Copy const qualifier from Source type to Target type.

 */

template< typename Target >

struct copy_const

{

   template< typename Source >

   struct from

   {

      using type = typename std::conditional<

       std::is_const< Source >::value,

       std::add_const_t< Target >, Target >::type;

   };

};

} //namespace TNL