public static extern void luna_unpackstruct(lua_State L, int index, int unpackFn, IntPtr data, StructElement *layout, int count);
public static extern void luna_getstruct(lua_State L, int idx, IntPtr data, StructElement *layout, int count);
public static extern void luna_packstruct(lua_State L, int newFn, IntPtr data, StructElement *layout, int count);
public static extern void luna_pushstruct(lua_State L, int metaRef, IntPtr data, StructElement *layout, int count);