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Maybe I'm wrong about how it works, but I feel that Optionals in Java are a bolt-on solution that only solves half the problem that the same concept solves in S
by wfleming 10y ago
Maybe I'm wrong about how it works, but I feel that Optionals in Java are a bolt-on solution that only solves half the problem that the same concept solves in Swift (or Haskell, or Rust, etc.)
An Optional in Java is just another value, and nothing in practice stops that from being null. I.e. a method that returns an Optional can still return an actual null if poorly implemented. So the major benefit Optionals give you in Java is a typed declaration that the method may return an "empty" value, which is certainly helpful for knowing what cases your client code needs to handle, but it does not guarantee that the method will never return null. It reduces the probability of unhandled null pointers, but it does not eliminate them.
On the other hand, Swift & co. guarantee at compile time that a function which says it returns an Optional will always return an an Optional, never a null, and, better still, if a function says it returns some non-optional value, it still is guaranteed to never return null.
It's great that Java is pushing for this style of code, but I'm afraid without compile-time guarantees of return values it will always feel less powerful there.
- lern_too_spel 10y agoUse JSR305 with Findbugs or SpotBugs to solve the problem at compile time. Using Optional in Java does have a problem with extra object overhead, so if you want to avoid that, you should use another language like Kotlin or Scala.
- Nullabillity 10y agoScala's Somes cost an object as well, though (I believe) None is free in both Java and Scala.
- lern_too_spel 10y agoYou're right. Some is not an AnyVal.
- hardwaresofton 10y agoI completely agree with your point -- you can't compare the power of compile-time checking to Java's Optionals, for the most part. However I tend to think that what's important about Optionals is the spreading of the notion of thinking critically about failure modes around improper input/output. "Defensive" coding is often considered a mid-range skill (at least I think), and IMO it's because a lot of junior programmers just assume if some method get ObjectThing a, it's going to be there, and not null. I think merely seeing Optional<ObjectThing> a encourages movement in the right direction as far as program correctness, a road that will almost surely tour through concepts and languages that take that kind of correctness more (ex. Swift, Haskell). Also, Optionals are a light introduction to functors which is nice. For more concrete actionable stuff please see other comment (https://news.ycombinator.com/item?id=13433335 https://news.ycombinator.com/item?id=13433335), there are tools that can do this at compile time for java
- ninjaroar 10y agoChecked exceptions also forces thinking critically about failure modes, but they seem to be an unpopular language feature, and few new libraries seem to use them. No other popular language has adopted them. Why are optionals good and checked exceptions bad? (I'm certainly not implying that one replaces the other - i'm just saying that it they both have an origin of forcing programmers to think about errors)
- stickfigure 10y agoBecause checked exceptions are incompatible with the idea of standard interfaces. You can't use interfaces like List, Iterable, Runnable, etc in a world with checked exceptions; you'd have to declare special versions of each of those interfaces for every possible exceptional condition. Since we need standard interfaces to let modules work together, everyone ends up catching and wrapping checked exceptions in runtime exceptions. Any potential value is lost. Exceptions are exceptional; the whole point is that you aren't supposed to have to think of them in normal program flow. Go gets this wrong too, forcing three extra lines of if err != null { for pretty much every single function call -- and with the added bonus of destroying stack context with each return.