A modern programming language that makes developers happier.

kotlinlang

<https://kotlinlang.slack.com/archives/C0B9K7EP2/p1589572019120700?thread_ts=1589398414.110200&amp;cid=C0B9K7EP2>

This is awesome! Really looking forward to this.

Is it not possible to have a syntax of the form `String | Int`  instead of `Union2&lt;String, Int&gt;`?

```
fun f(): Union2&lt;String, Union2&lt;Int, Double&gt;&gt; = 2
           fun y(): Union3&lt;String, Int, Double&gt; = f()
           fun x(): Int? = y()
```
Shouldn’t `x()` produce a type mismatch compilation error since `y()` may return types that are not `Int?`?

&gt;  Shouldn’t `x()` produce a type mismatch compilation error since `y()` may return types that are not `Int?`?
If they do it simply results in null.
That is one of the proofs defined in the prelude.

<https://github.com/arrow-kt/arrow-meta/blob/master/prelude/src/main/kotlin/arrow/union/nullables.kt>

In other words there is a proof to unbox a Union to a given type, if it is part of the union.

It won’t let you unbox to a type that is not in the union, but if the type is in the union you access it safely with its nullable type without matching or folding in all cases

A bit poorly phrased from my side. :smile: I get why that could be misunderstood.