3 ms·

Except this is completely wrong. First, a record can't extend anything, it's not even valid syntax, so a sealed class can't permit record subclasses. So no, it

Except this is completely wrong. First, a record can't extend anything, it's not even valid syntax, so a sealed class can't permit record subclasses. So no, it's not possible to create a Maybe<T> class in Java that can only represent a Some<T> or a None<T> record. You could do it with regular classes, or if it's ok for Maybe<T> to be an interface. Secondly, regardless of the sealing, nothing in any current or near future of Java prevents you from assigning `null` to any class of any kind you might create. So you can always have `Maybe<T> x = null`, or even `Some<T> x = null`. None of this will change with the adoption of value classes either. So no, there is absolutely no way in Java to create a real Optional/Maybe type that would guarantee that a variable is either an object of a given type or None. There is probably some way to do it for your specific project using annotation processors, of course, but that is very different from having built-in support.

gf000 4mo ago
Mistyped, it's sealed interface. > So you can always have `Maybe<T> x = null`, or even `Some<T> x = null`. Yeah and? Practically every type system have escape hatches, like Haskell can also do side effects without the IO monad, does it make the latter useless?
- tsimionescu 4mo ago
  The whole point of using Optional/Maybe is to prevent the possibility of accidemtally creating nulls. If you don't make mistakes, then nullability is not a problem. If you do make mistakes, then a class that only helps when you don't make mistakes is basically useless. This also has significant impact for serialization/de serialization - a classic place where you get unexpected nulls, that Java Optional/Maybe don't help with at all.
  - joe_mwangi 4mo ago
    Since they plan to have null-restricted types, then I don't see any issue.
    - Dylan16807 4mo ago
      > plan to Well wasn't that the argument above, that the stuff they added so far isn't proper at least in part because they didn't fix that problem yet?
      - joe_mwangi 4mo ago
        > yet But up the comment section, someone thinks they won't be there 'in the future'
        Dylan16807 4mo ago
        The comment that says it won't be there in the near future? That's seems like a reasonable claim to me. And a promise to eventually fix a busted implementation doesn't undo it being busted for a significant amount of time.
        joe_mwangi 4mo ago
        Better late than never.
  - gf000 4mo ago
    Disagree. Types are both for the compiler, as well as for the developer. Maybe types are implicit documentation telling the developer that it is meaningful in the application that this field can have a None state. That's a huge code smell to ever set null to an Optional/Maybe and code reviews, linters, nullness analyzers all should/will flag such. Like I have never ever had an NPE from an Optional being null. Sure, complete null safety would be better of course, but in this very instance it ain't buying you much.
    - mrkeen 4mo ago
      This is what your choices are with regard to communicating to the compiler and other developers. Use a regular class to signal that you may or may not have a value. Wrap it in an optional to signal that you may or may not have a value. See the problem?
munksbeer 4mo ago
It's probably a typo. He meant sealed interface. I think that should be quite obvious.

gf000 4mo ago

Mistyped, it's sealed interface. > So you can always have `Maybe<T> x = null`, or even `Some<T> x = null`. Yeah and? Practically every type system have escape hatches, like Haskell can also do side effects without the IO monad, does it make the latter useless?

tsimionescu 4mo ago
The whole point of using Optional/Maybe is to prevent the possibility of accidemtally creating nulls. If you don't make mistakes, then nullability is not a problem. If you do make mistakes, then a class that only helps when you don't make mistakes is basically useless. This also has significant impact for serialization/de serialization - a classic place where you get unexpected nulls, that Java Optional/Maybe don't help with at all.
- joe_mwangi 4mo ago
  Since they plan to have null-restricted types, then I don't see any issue.
  - Dylan16807 4mo ago
    > plan to Well wasn't that the argument above, that the stuff they added so far isn't proper at least in part because they didn't fix that problem yet?
    - joe_mwangi 4mo ago
      > yet But up the comment section, someone thinks they won't be there 'in the future'
      - Dylan16807 4mo ago
        The comment that says it won't be there in the near future? That's seems like a reasonable claim to me. And a promise to eventually fix a busted implementation doesn't undo it being busted for a significant amount of time.
        joe_mwangi 4mo ago
        Better late than never.
- gf000 4mo ago
  Disagree. Types are both for the compiler, as well as for the developer. Maybe types are implicit documentation telling the developer that it is meaningful in the application that this field can have a None state. That's a huge code smell to ever set null to an Optional/Maybe and code reviews, linters, nullness analyzers all should/will flag such. Like I have never ever had an NPE from an Optional being null. Sure, complete null safety would be better of course, but in this very instance it ain't buying you much.
  - mrkeen 4mo ago
    This is what your choices are with regard to communicating to the compiler and other developers. Use a regular class to signal that you may or may not have a value. Wrap it in an optional to signal that you may or may not have a value. See the problem?

munksbeer 4mo ago

It's probably a typo. He meant sealed interface. I think that should be quite obvious.