If you're gong to the trouble to use an overlay structure to represent the serialization of an object, then the most optimal thing to do is to perform the endia

If you're gong to the trouble to use an overlay structure to represent the serialization of an object, then the most optimal thing to do is to perform the endianness conversion once at the boundary between the outside world and the program. Adding type annotations encourages a coding style that makes many conversions at every point of use, instead of only once at the boundary.