``` SWIFT enum NumberCategory case Small case Medium case Bi

Question

``` SWIFT enum NumberCategory case Small case Medium case Big case Huge init number n Int if n lt 10000 self = Small else if n lt 1000000 self = Medium else if n lt 100000000 self = Big else self = Huge ``` How I can achieve something like this in kotlin Just to illustrate my problem I have a bunch of business logic conditionals that I want to convert to a type and send it to my view I m not even sure if this is the best solution or I stick with boolean methods

benleggiero · Answer

``` enum class NumberCategory Small Medium Big Huge companion object operator fun invoke n Int = if n lt 10000 Small else if n lt 1000000 Medium else if n lt 100000000 Big else Huge ```

elizarov · Answer

It would be even more kotlin if you rewrite it using `when` And even more compliant to official Kotlin style if you use top level constructor like function named `NumberCategory` instead of `companion object`

benleggiero · Answer

How is a top level function named the same as the class name any more Kotlin than an invoke operator function

elizarov · Answer

That is approach that is used in Kotlin standard library and is generally a preferred one it is easier to understand and does not look as magic

benleggiero · Answer

I don t think a language feature as simple as an `operator fun` is magic Perhaps if it s seen as such by the writers of stdlib then it should be rethought Perhaps we should allow factory style constructors

elizarov · Answer

Magic here means harder to understand for novices `operator fun invoke` is a useful feature for certain DSL but using it just to define a factory function requires too much syntax and boilerplate A top level function with the corresponding name solves the same problem simpler more directly with less code

benleggiero · Answer

Wait so why would stdlib use it If there use site is identical then you mean the novices are the ones writing the library not the ones using it Also something I dislike about that approach is the IDE syntax highlighting it as a function when it s used as a constructor

elizarov · Answer

Stdlib is using constructor functions take a look here for example <https kotlinlang org api latest jvm stdlib kotlin collections list html>

elizarov · Answer

It is an open design question on better integration of those constructor functions into the language itself Currently it is just a convention

benleggiero · Answer

I think it s silly for the same team presumably that went through the trouble of inventing approving the invoke pattern which does this thing they are mimicking would not use it because they think it s too complicated Says a lot

elizarov · Answer

I m not sure I understand your idea `operator fun invoke` was primarily designed for function like objects and classes all function types have it for example Using it on `companion object` is clever hack indeed but understandable software should not be built using clever hacks

benleggiero · Answer

Sure and the JVM was primarily designed for webpage applets but we found much better uses for it I don t think it s a clever hack using it this way This seems very intended If it wasn t intended I d expect its syntax to be `MyClass Companion arguments ` but it s `MyClass arguments `