[Groxx]

Java's main issue is that its `throws` isn't generic. It forces middleware-like code to choose between `throws Exception` and runtime-only plus boxing... both of which lose ALL details and ruin your compile-time safety.

IMO it just poisoned the well, and now everyone* thinks they don't like checked exceptions, when really they just don't like Java's badly crippled version.

[ragnese]

You can have generic `throws` markers; e.g.,

    interface Frobinicator<E extends Exception> {
        void frobinicate() throws E;
    }

[Groxx]

Which gives you a single exception type, not a list. Squashing the list of possibilities rather uselessly.

You can work around this with N `T extends Exception`s, but now you have to pick the correct one all the time. And e.g. using it in a `map`-style stream with a final collected throw means picking whether you're adding type N or not. Or possibly multiple new types. It rapidly grows to be unusable.

You also can't make a `class MyException<T>`. Or do a `catch (T e)`. There are a lot of blockages in practice to trying to do any of this - exceptions are very special in the type system, which is the problem.

[ragnese]

You definitely won't find me defending Java too often. And I certainly agree that there are frustrating limitations. Like you said, it's annoying that Java does have ad-hoc union types, but only for the throws list in function signatures and for the type specification in catch blocks. So, it's definitely painful that you can't use a similar syntax when implementing something like the generic interface example I wrote.

> You also can't make a `class MyException<T>`. Or do a `catch (T e)`. There are a lot of blockages in practice to trying to do any of this - exceptions are very special in the type system, which is the problem.

Agreed.

But, my entire contention with the discussion around checked exceptions is that everyone found some sharp edges and limitations with Java's checked exceptions and instead of deciding that Java suck{ed,s}, everyone seemed to decide that checked exceptions suck. That was the wrong conclusion, IMO, and I truly believe it has slowed progress in programming language design.

It's only recently that statically typed failure modes are becoming mainstream again (e.g., Rust, Swift, and many third-party libraries for languages like TypeScript and Kotlin among others).

Speaking of streams and combinators like map, Swift has the `rethrows` keyword which is absolutely awesome, IMO. It's this kind of progress that I think we've missed out on from everyone rejecting checked exceptions as a concept for the last decade or so. We threw the baby out with the bathwater.

[Groxx]

>... instead of deciding that Java suck{ed,s}, everyone seemed to decide that checked exceptions suck.

Oh yes, absolutely agreed. It's particularly strange when it comes from people talking about how amazing Rust/Swift/etc ADT errors are - if implemented in a reasonable way, they're expressively identical, so it just becomes "do you like exceptions or returns" and that's much more opinion than fact. Java's checked exceptions are factually bad.