#include <type_traits>

template <typename Type, typename... Types>
struct largest_type
{
    using type = std::conditional_t<
        (sizeof(Type) > sizeof(typename largest_type<Types...>::type)),
            Type, typename largest_type<Types...>::type >;
};

template <typename Type>
struct largest_type<Type>
{
    using type = Type;
};

template <typename... Types>
using largest_type_t = typename largest_type<Types...>::type;

int main()
{
    static_assert( std::is_same_v< largest_type<int>::type, int > );
    
    static_assert( std::is_same_v< largest_type_t<int>, int > );
    static_assert( std::is_same_v< largest_type_t<int, char>, int > );
    static_assert( std::is_same_v< largest_type_t<int, char, double>, double > );
}