Call chain on collection could be converted into 'Sequence' to improve performance

Reports call chain on a Collection that should be converted into Sequence.

Each Collection transforming function (such as map() or filter()) creates a new Collection (typically List or Set) under the hood. In case of multiple consequent calls, and a huge number of items in Collection, memory traffic might be significant. In such a case, using Sequence is preferred.

Example:

class Entity(val key: String, val value: String)

fun getValues(lines: List<String>) = lines
    .filter { it.isNotEmpty() }
    .map { it.split(',', limit = 2) }
    .filter { it.size == 2 }
    .map { Entity(it[0], it[1]) }

The quick-fix wraps call chain into asSequence() and toList():

class Entity(val key: String, val value: String)

fun getValues(lines: List<String>) = lines
    .asSequence()
    .filter { it.isNotEmpty() }
    .map { it.split(',', limit = 2) }
    .filter { it.size == 2 }
    .map { Entity(it[0], it[1]) }
    .toList()

Inspection options

Option	Type	Default
Call chain length to transform	Number	5

Inspection Details
Available in:	IntelliJ IDEA 2023.3, Qodana for JVM 2023.3
Plugin:	Kotlin, @snapshot@

Last modified: 13 July 2023