Optionals that throw NPEs, Streams that operate on more than 1 item when called with .limit(1). Futures that don't cancel. Lambdas that don't play nicely with exceptions. Non-extendable streams.
"Poorly" is very subjective. Yes, some aspects require fixing (e.g. the interaction of lambdas with checked exceptions; there's much we can do there, but we need to design this carefully), but others are tradeoffs; e.g. they require complicating the language in a way that hurts in other areas.
It's not a coincidence that many languages that PL fans think do things "right" end up being far less popular than languages that PL fans think do things "wrong". Developers have different and conflicting preferences, and they are not distributed evenly. For example, the sweet spot for mainstream, super-popular languages over more/less compile-time checking in some areas vs. language complexity is probably not the sweet spot preferred by most developers. It's a little like the VHS vs. Betamax debate.
Improving a super-popular language in some small way that doesn't harm its popularity can have a far bigger impact on software quality than features that complicate the language to a point where it will not be taught as a first language in a lot of schools and will thus never be super-popular. Designing language features for industry to maximise their impact requires far more complex considerations than just PL theory.
> Yes, some aspects require fixing (e.g. the interaction of lambdas with checked exceptions; there's much we can do there, but we need to design this carefully)
I do like the Java platform in general, but this sort of argument from hypothetical future Java fixes strikes my as incredibly disingenuous. People aren't programming in a hypothetical future Java.
I can literally pose no argument against your imagined solution to this problem without very specific details. (Implication being, it's a straw man at best.)
And saying saying stuff like (in an adjacent thread):
> You're assuming that deconstructing and exhaustive patterns will continue to be restricted to ADTs only. That may or may not be the case.
Is just complete fiction. (EDIT: Are you going to solve the halting problem, or are you going to provide details before just promising "it'll be ok"? I assume the Halting Problem is out of the question, but what's the plan, then? Details, pls)
Either point to extant JEPs or explain in detail what the exact plan is, please.
First of all, you completely misunderstand my point. I neither ask people to judge Java based on some hypothetical future, nor ask for feedback on future designs. I acknowledged there's a real problem and mentioned we're exploring solutions, but even with the problem Java is the world's most popular typed programming language in 2023. Not every problem is big, and PL fans tend to grossly overestimate the cost of some cumbersomeness in a language and grossly underestimate the cost of language complexity because their preferences are often in the minority.
Having said that, we have a few experiments with type-safe "checked exception transparency" for lambdas (and methods in general), but as always we like to sit on them for a few years because the cost of a bad feature may be much higher than the cost of a missing one. We only publicly discuss specific solutions once there's something to be gained by such a discussion and once we've decided that the problem merits a solution in the short term.
Either way it feels like optionals are going to be deprecated real quick now we have sealed interfaces and record matching. They let you get rid of so much of the unpleasantness in dealing with this API. Instead you can
public sealed interface Maybe<T> {
<T2> Maybe<T2> map(Function<T, T2> mapper);
<T2> Maybe<T2> flatMap(Function<T, Maybe<T2>> mapper);
T elseGet(T fallback);
record Just<T>(T value) implements Maybe<T> {
public <T2> Maybe<T2> map(Function<T, T2> mapper) {
return new Just<T2>(mapper.apply(value));
}
public <T2> Maybe<T2> flatMap(Function<T, Maybe<T2>> mapper) {
return mapper.apply(value);
}
public T elseGet(T fallback) {
return value;
}
}
record Empty<T>() implements Maybe<T> {
public <T2> Maybe<T2> map(Function<T, T2> mapper) {
return new Empty<>();
}
public <T2> Maybe<T2> flatMap(Function<T, Maybe<T2>> mapper) {
return new Empty<>();
}
public T elseGet(T fallback) {
return fallback;
}
}
}
public void demo() {
Maybe<String> foo = new Maybe.Empty<String>();
System.out.println(
switch (foo) {
case Maybe.Just(String val) -> "Hello " + val;
case Maybe.Empty() -> "Fine, leave me hanging";
}
);
};
Java started with Records + improved switch expressions to pave the way for Pattern matching, but the feature is far from being done. Deconstruction patterns for classes are being worked. In fact, Optional has been brought up as an example in internal discussions time and time again.
The way Pattern matching works right now is just the beginning.
Showing an error on broken code will cost you backwards compatibility.
The best you will get is a warning and the JVM will deoptimize Optional back to a regular object, because somewhere someone set an Optional to null somewhere in a library. It doesn't even have to be as obvious as Optional<String> o = null;
Any cast to Optional can let a null pointer slip from an Object reference. List<Optional<String>> is allowed to contain null pointers and you are allowed to assign o = list.get(0) which generates an implicit cast.
There is no good solution for this. Due to the way generics are implemented.
Ah, you mean the Optional itself being null. That’s not any bigger an issue than anything else being Optional. Also, value types might come combined with nullability — so you might have Optional<String>!, which can’t be null, and will efficiently be stored in-place.
However, unlike the binary choice of class/value type, project valhalla will provide a more granular approach, coming with incremental performance benefits and constraints.
In the current spec draft, the type system boils down to 4 categories:
Optionals that throw NPEs, Streams that operate on more than 1 item when called with .limit(1). Futures that don't cancel. Lambdas that don't play nicely with exceptions. Non-extendable streams.