> It is literally impossible to "forget" if you have pattern matching + algebraic data types/enum/unions.No, it's entirely possible to forget. That should be obvious. It is a functional necessity for you to be able to forget as you can only type so much at a time. You cannot possibly write code to call a function and perform pattern matching on the result at the exact same moment in time. There fundamentally has to be a period of time where the work will be incomplete, which opens the opportunity to not finish. It should be abundantly apparent to you that that you can forget to finish what you started in such a scenario.
Your checks and balances will alert you of your forgetfulness, but that's true of all languages. The biggest risk is that you will forget to define behaviour. But if you fail to do that, you've got problems even in languages with pattern matching and associated types. ADTs/enums/unions/pattern matching. are not sufficient to define behaviour. Not even close.
Like you said, pattern matching only helps you with checking errors. But there is no reason to check errors in the first place if you don't do something with the error, and for that you need to document what the error condition means for the user. Otherwise you have undefined behaviour. And once you've documented the behaviour, the error checks are confirmed for free anyway. You can't forget. The checks and balances will make it known, spectacularly.
What, exactly, are you trying to accomplish by overselling what is already a fantastic feature by its own merits on the basis of something that isn't at all realistic? If you want to get developers excited about the feature, there are way more compelling attributes to extol!
I have read this exact claim before, for what it is worth. Did you end up here simply because you repeated what you saw elsewhere without actually thinking about it?
