[piaste]

Password validation is a degenerate case of parsing, where your parsed type does not contain any more information than your unparsed type - both are just opaque strings.

(In fact you could use an invalid password just fine: unless you're doing something really weird, your code would not misbehave because it's too short or missing digits and symbols. It's only due to security reasons that you choose to reject that string.)

But that doesn't mean that `string -> Password` isn't parsing! As long as you're outputting distinct types for ValidPassword and InvalidPassword, you are still following the advice of this article, because you can make all your internal code use ValidPassword as a type and you will not need to ever check for password validity again.*

Compare that to e.g. adding a { IsValid = true } field to the object, which would require you to defensively sprinkle `if (user.Password.IsValid)` every time you try to actually use the password field.

* One weakness arising from the fact that this is degenerate parsing, i.e. ValidPassword is just a string, is that a very stubborn fool could build a ValidPassword from any arbitrary string instead of using the proper parse function. Depending on your language, this can be prevented by e.g. hiding the constructor so that only parsePassword has access to it.

[crabbone]

> Password validation is a degenerate case of parsing

Really? How is that degenerate? Compared to what?

My guess is that you just decided to use a dictionary word you don't fully understand.

> In fact you could use an invalid password

Where does this nonsense come from? No. I cannot use invalid password. That's the whole point of validation: making sure it doesn't happen. What kind of bs is this?

> But that doesn't mean that `string -> Password` isn't parsing!

It's doing nothing useful, and that's the whole point. You just patted yourself on the head in front of the mirror for using some programming technique that you believe makes you special, but accomplished nothing of value. That was the original point: if you want results, you will end up doing validation, there's no way around it. You renaming of types is only interesting to you and a group of people who are interested in types, but doesn't advance the cause of someone who wants their password validated.