Theoretically, Kotlin and Java could allow for discriminated unions if they would permit for public constructors.

It does not create a new type, but provides an alternative name for an existing one, which can make. Just to say, I’m not generally against non discriminated unions, indeed they make sense in certain situations like for enumerations.Įdit: It is theoretically possible to introduce subtyping for discriminated union types, but most languages simply won’t do it. Use typealias n Kotlin, a type alias is a way to create a new name for an existing type. The problem with this is, is nominal wrapping usually destroys subtyping relationships between union types and between union and other types.įurthermore, unlike untagged non-disjoint union types (typescript unions), you can’t easily construct them by assignment, e.g. So, you can’t have union type between unrelated classes ( String|Int for example).ĭiscriminated unions aka disjoint tagged union types aka enums can cope with unrelated types, but they require a nominal tag to disambiguate akin to Rust’s Enums. Here, findFirst returns an Optional, and thenįile if one exists.I read it well, discriminated unions are “just” sealed type. Not yet been processed, and then opens that file, returning an

For example, theįollowing code traverses a stream of file names, selects one that has The need to explicitly check for a return status. Kotlin Data Types In Kotlin, the type of a variable is decided by its value: Example val myNum 5 // Int val myDoubleNum 5. API Note: This method supports post-processing on optional values, without If a value is present, apply the provided mapping function to it,Īnd if the result is non-null, return an Optional describing the

Kotlin type any