I need to do a set of list operations and I want those methods to be pure with taking List as input ...

# codereview

[BMG]

I need to do a set of list operations and I want those methods to be pure with taking List as input and giving List as output and they have to be chained. Can this be improved?

val updatedDataElementsOne = removeExtraElements(info)
val updatedDataElementsTwo = updateExistingElements(updatedDataElementsOne)
return populateEmptyElements(updatedDataElementsTwo)

[bitkid]

info.filter{}.map{} or something like this?

[Andreas Sinz]

You can define them as extension functions and use them like

fun List<T>.removeExtraElements(): List<T> {
    //Do work
    //Return new list
}

fun List<T>.updateExistingElements(): List<T> {
    //Do work
    //Return new list
}
//usage
list.removeExtraElements().updateExistingElements()

[BMG]

@bitkid I couldn’t do populate operation in that chain where I need to add some elements at the end of the list.

@Andreas Sinz I assumed that extensions were overkill for this. But I really like the chaining ability it gives!

[Andreas Sinz]

Just try to limit the number/the visibility of extensions on common types like List<T>, otherwise you end up with a huge list of entries in code completion

[Andreas Sinz]

what actions do you have to do on the list? maybe we can work something out with standard extension functions

[BMG]

Sure, I made them private extensions. I have mainly three operations with some business logic,

1) update elements
2) remove elements at the end (dropLast)
3) add some elements at the end

[Andreas Sinz]

what about

list.map { //Update elements }
     .dropLast(10)
     .run { this + listOf(a, b, c) }

[BMG]

Correct, but I have some business logic before doing each of them which I wanted to pull out as functions. Like,

list
.mapIndexed {
   // 10 lines of code which modifies each element
}
.dropLast {
   calculatedNumberOfElementsToRemove()
}
.run {
// 10 lines of code to add new elements
}

[BMG]

Now I’m thinking I can just pull those 10 lines of code as a function instead of extension

[dave08]

If the function has the exact same inputs and outputs as mapIndexed say, then you could just call it mapIndexed(businessLogicObjInstance::myFunction). You then avoid the extra lambda.