[lexi-lambda]

> If you can't create a value of type PrimeNumber that doesn't contain a prime number, there's a bit more to it than naming.

Yes, indeed. This is quite useful! But crabbone isn’t entirely wrong that it isn’t quite what the original article was about.

I’ve written quite a bit of code where constructive data modeling (which is what the original article is really about) was both practical and useful. Obviously it is not a practical approach everywhere, and there are lots of examples where other techniques are necessary. But it would be quite silly to write it off as useless outside of toy examples. A pretty massive number of domain concepts really can be modeled constructively!

But when they can’t, using encapsulation to accomplish similar things is absolutely a helpful approach. It’s just important to be thoughtful about what guarantees you’re actually getting. I wrote more about that in a followup post here: https://lexi-lambda.github.io/blog/2020/11/01/names-are-not-...