intellij-ideakotlinsetcode-inspectionintellij-inspections

Why does IntelliJ suggest to convert a call chain into a Sequence?


Assume the following Kotlin example that maps the source set src to a destination set dst:

private val src: Set<String> = setOf("hello", "world")
private val dst: Set<Int> = src.map { it.length }.toSet()

This works fine. However, IntelliJ's code inspection suggests: Call chain on collection should be converted into 'Sequence':

Call chain on collection should be converted into 'Sequence'

Applying this suggestion results in

private val dst: Set<Int> = src.asSequence().map { it.length }.toSet()

What is the benefit of this?


Solution

  • In this case the suggestion is suboptimal. The correct way to rewrite this code (which also doesn't result in any IntelliJ warnings) is:

    src.mapTo(hashSetOf()) { it.length }
    

    This will avoid the creation of an intermediate list that will be subsequently converted to a set; the data will be added to the resulting set right away.