Oh I see, I admit my understanding of the struct editing situation is spotty at best, and I was recalling this thread in particular. I take back my suggestion to edit the blog post to explain the difficulty of struct editing, though it would be worth adding a sentence to mention Revise.jl and the fact it handles editing of methods but not structs.
Replacing the module is also mentioned in Revise.jl’s issue #18 as problematic. It’s not particular to structs, preexisting code that uses the old module will still use the old module even if its name is attached to a new module, and if you attempt to using the new module via the same name, you’ll get identifier conflict warnings and “both ModuleName and ModuleName export …” errors. And as you mentioned, there’s the problem of the obsolete types’ persistent instances (a problem that is also true for the more dynamic interpreted languages). But I do wonder why there aren’t module backedges+invalidations+reruns as a way to deal with edited structs; it just seems like an obvious development from the discussion in issue #18, and rerunning affected modules seems better than a full restart.
But this is starting to be a bit removed from the main topic, so if anybody wants to clarify this stuff for laypeople like me, feel free to split this to another topic.