>Unfortunately, it is not really possible to change Kotlin behave the same way. Apple uses a bridging mechanism to connect Objective-C and Swift binaries, when Kotlin uses the same bytecode as Java. To make a simpler mental picture, imagine Objective-C and Swift being connected side-by-side and Kotlin and Java as a stack, where Kotlin is on top. I presume it would be pretty challenging to provide a proper compatibility with Java, transforming all nullable Kotlin values to Optional and vice-versa, especially in such tight areas like Java reflection.
This is not correct. The Kotlin compiler could treat every parameter and return value that doesn't have a nullability annotation as an implicitly unwrapped optional (Type!). It could even support all of the popular nullability annotations. There is no requirement to choose just one.
The beauty of IUO is that you can ignore the nullability and you have the same amount of safety you have today: if you touch a null value you get an exception (or abort in Swift's case). The benefit is you can insert a null check in one place which then propagates through the rest of your Kotlin (or Swift) code.
I wrote a post a few years ago comparing nullable types to maybe/optional. https://www.lucidchart.com/techblog/2015/08/31/the-worst-mis...
A lot of it is a more specific cas of sum types vs union types.
They could have gone hardcore and said any non-primitive, unanotated platform type is nullable but that would have made interop really ugly. And all of the null checks would have muddied up code and added (admittedly minimal) runtime costs.
I want something in between Kotlin and Scala. I want option as a real type that is treated as a max-single-element collection that can be flattened with the same APIs as other collections. But I want no runtime penalty. People in Rust are so lucky to have zero cost abstractions for these things. I suppose I'll need better compile time support (even more than Scala macros) and whole program optimizations (i.e. cross JAR) to get zero cost optional on the JVM. Things like Scala Native use LLVM and surely Option things are inlined or otherwise optimized out.
Shameless little self promotion
"Comparing Optionals and Null in Swift, Scala, Ceylon and Kotlin"
Personally I like Monads better than the Kotlin solution. Best is probably the way Swift does it.
>Turns out Swift does not have null pointers. At all!
Mostly true under the hood; optional value types are tagged unions (I didn't know this before reading this article and checking for myself), but optional reference types are still, as you'd expect, nullable pointers.
Well, the null issues in Java libraries have always been there, I don't really think it's a fault of Kotlin and its tooling that those bugs are not caught at all by the compiler, as all object types in Java are Kotlin optionals if not annotated.
Maybe in time most of the necessary open source projects will be pure Kotlin ones, but for now I believe annotating Java code with null constraints is certainly a boon for everyone and should be encouraged.
At least for android kotlin programming, with the release of api level 27 + support libraries, it’s a lot better. They have placed the annotations all over the place. Using nullable annotations have good use cases in java too.
I would think optional types and everything else being non nullable is the way forward for java too
After coding enough Crystal, which instead of optionals have raw and anonymous sum types, I can say this: I don't see the point of a type system where nil is a special case. I don't want optionals, I want to have nil as a totally separate type.
I don't quite get the problem as stated in the article. I assume it's a contrived example and the real (kotlin) code rather looks like:
Here foo is defined as nullable, hence the problem. If you make it
val foo: T? = null Observable.just(foo).subscribe()
the kotlin compiler will bark on foo being null and you'll never have a runtime error.
val foo: T = null Observable.just(foo).subscribe()
I think the motivating example should be described better but maybe I misunderstand it.
It seems like a good article but the grammar makes it difficult to read at times.
Aren't null pointers just a variation on the Maybe Monad?
.online is a terrible TLD.
The java compiler might not know if a variable is safe to pass as null, but it is not unknowable. I think on every thread similar to this that I am on, I have plugged Coverity as a tool that can and will flag spots like this. That is, it won't just say "it is possible this will be a null pointer exception," instead it will say "setting this value to null will lead to this dereference of a null." It can look magical sometimes, because they will trace pretty deeply into your code.
Which is just my way of saying over and over again that tooling can improve that does not require a complete rewrite of your software.