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()

Locating this inspection

By ID

Can be used to locate inspection in e.g. Qodana configuration files, where you can quickly enable or disable it, or adjust its settings.

ConvertCallChainIntoSequence

Via Settings dialog

Path to the inspection settings via IntelliJ Platform IDE Settings dialog, when you need to adjust inspection settings directly from your IDE.

Settings or Preferences | Editor | Inspections | Kotlin | Style issues

Inspection options

Here you can find the description of settings available for the Call chain on collection could be converted into 'Sequence' to improve performance inspection, and the reference of their default values.

Call chain length to transform: Default value:
5

Suppressing Inspection

You can suppress this inspection by placing the following comment marker before the code fragment where you no longer want messages from this inspection to appear:

//noinspection ConvertCallChainIntoSequence

More detailed instructions as well as other ways and options that you have can be found in the product documentation:

IntelliJ IDEA 2025.2

Inspection Details
By default bundled with:	IntelliJ IDEA 2025.2, Qodana for JVM 2025.2,

Last modified: 18 September 2025