Data type extensibility and composition

[pavel.kirienko]

@scottdixon

I’d rather make @sealed the default since this also gets rid of the default extent formula and makes naive implementations or prototyping with UAVCAN more immediate and successful. It seems like any datatype author would start with a prototype and only need to think about the future when finalizing a design. It’s in this later phase of a project that one would take the time to calculate extents properly.

I think your assumption that a developer would sit down and think about the future is unsound. My experience indicates that people rarely do that, so we should either force them to (make @extent required) or do it for them (default extent plus the tooling approach).

So I think that here:

I think either the tooling approach or making @sealed the default are the best options.

We can agree on the first option. If this is so, I am going to update the PyDSDL PR with the diagnostic.