[samatman]

The One True Wiki[0] says "Used to describe an implementation that needlessly relies on strings when programmer & refactor friendly options are available."

Which is exactly what's going on here. A username has a string as a payload, but that payload has restrictions (not every string will do) and methods which expect a username should get a username, not any old string.

[0]: https://wiki.c2.com/?StringlyTyped

[tdeck]

I don't agree that this example is more "programmer friendly". Anything you want to do with the username other than null check and passing an argument is going to be based directly on the string representation. Insert into a database? String. Display in a UI? String. Compare? String comparison. Sort? String sort. Is it really more "programmer friendly" to create wrapper types for individual strings all over your codebase that need to have passthrough methods for all the common string methods? One could argue that it's worth the tradeoff but this C2 definition is far from helpful in setting a clear boundary.

Meanwhile the real world usages of this term I've seen in the past have all been things like enums as strings, lists as strings, numbers as strings, etc... Not arbitrary textual inputs from the user.

[cwilkes]

You inherit some code. Is that string a username or a phone number? Who knows. Someone accidentally swapped two parameter values. Now the phone number is a username and you’ve got a headache of trying to figure out what’s wrong.

By having stronger types this won’t come up as a problem. You don’t have to rely on having the best programmers in the world that never make mistakes (tm) to be on your team and instead rely on the computer making guard rails for you so you can’t screw up minor things like that.

[quickthrower2]

I agree on the one hand but empirically I don’t think I have seen a bug where the problem was the string for X ended up being used as Y. Probably because the variable/field names do enough heavy lifting. But if your language makes it easy to wrap I say why not. It might aid readability and maybe avoid a bug.

I would probably type to the level of Url, Email, Name but not PersonProfileTwitterLink.

[baq]

I’ve refactored a large js code base into ts. Found one such bug for every ~2kloc. The obvious ones are found quickly in untyped code, the problem is in rare cases where you e.g. check truthiness on something that ends up always true.

[quickthrower2]

Of those bugs I wondered how much a type would help. For example is it a misunderstanding of business requirements (nosurcharge bool = iscash bool) or a “typo” / copy paste error. If the former types don’t help. The latter they might.

[nogridbag]

It definitely helps in larger applications where things are named similarly, especially if you're dealing with a massive DB schema. If you have some method to update some data where all the PRs are longs and it has the signature "update(long,long)", passing the wrong long value would be disastrous. Even if this type of error is 1:10k LOC, using wrapper classes pretty much eliminates this bug.

In our codebase, we use wrapper classes and the only time we had a defect with this is when one developer got lazy and used 3 primitive Strings in a class instead of wrapper classes. Another developer needed to update the code and populated the wrong wrapper class as they were not as familiar with that part of the codebase. Had the original developer simply used wrapper classes, the person maintaining the code wouldn't have had that confusion.

[antonvs]

> Is it really more "programmer friendly" to create wrapper types for individual strings all over your codebase that need to have passthrough methods for all the common string methods?

That can be handled transparently in languages that have good support for strong type systems, like Rust or Haskell, using traits or type classes.

What you're saying is essentially that addressing stringly typing can only be taken so far in weakly typed languages, without becoming inconvenient.

> Meanwhile the real world usages of this term I've seen in the past have all been things like enums as strings, lists as strings, numbers as strings, etc... Not arbitrary textual inputs from the user.

The definitional question is not that interesting. The point is that the concept applies just as much to a username represented as a string as it does to any other kind of value being represented as a string.

The reason is simple, which is just that "string" is a general type that can represent anything, whereas "username" is a subset of all possible strings. If you're trying to use your type system to ensure correct code, you want to be able to type check a function signature like `f(user, company, motto)`, just to take a simple example.