Kotlin - adding map function conditionally-CodePudding

I would like to feature toggle a map function on a list. I have a map that I would like to run only if the feature is on: So for something like this:

items
     .map { doTransformation(it) } 
     .map { runOnlyIfFeatureIsOn(it) }

Is there a way of adding the whole .map function conditionally in kotlin, so that it is only there if it is feature toggled?

CodePudding user response：

Maybe just do if in map? There is no problem with that:

val list = listOf(1, 2, 3)

    list
        .map { it * 2 }
        .map {
            if (featureIsOn) {
                runFeatureMapping(it)
            } else {
                it
            }
        }

CodePudding user response：

let() is handy for doing arbitrary processing in a pipeline, e.g.:

items
    .map{ doTransformation(it) } 
    .let{ if (someCondition) it.map{ runOnlyIfFeatureIsOn(it) } else it }

(For complex/costly conditions, this will be more efficient than putting the if inside the map call, as this'll only evaluate the condition once.)

CodePudding user response：

Using sequences:

var sequence = items.asSequence()
    .map { doTransformation(it) }

if (<feature_1_enabled>) {
    sequence = sequence.map { runOnlyIfFeature1IsOn(it) }
}

if (<feature_2_enabled>) {
    sequence = sequence.map { runOnlyIfFeature2IsOn(it) }
}

val result = sequence.toList()

Sequences are lazy-evaluated and should be used when mutliple operations (filter/map/etc) are applied