fix: index_tuple metafunctions as index_tuple aliases (if Template-aliases enabled)

sprout/detail/sizeof.hpp

@@ -0,0 +1,17 @@
+#ifndef SPROUT_DETAIL_SIZEOF_HPP
+#define SPROUT_DETAIL_SIZEOF_HPP
+
+#include <cstddef>
+#include <type_traits>
+#include <sprout/config.hpp>
+
+namespace sprout {
+	namespace detail {
+		template<typename... Ts>
+		struct sizeof_pack
+			: public std::integral_constant<std::size_t, sizeof...(Ts)>
+		{};
+	}	// namespace detail
+}	// namespace sprout
+
+#endif	// #ifndef SPROUT_DETAIL_SIZEOF_HPP