Replace 'map { it.key }.toSet()' with 'keys'

Reports map { it.key }.toSet() call chains on map receivers that could be replaced with keys.

Note: While this transformation is beneficial for readability and performance, as it avoids unnecessary intermediate collections, it may change call semantics because keys returns a read-only view of the map's keys, whereas the original call chain creates a copy of the keys.

The quick-fix replaces the call chain with the map's keys property.

Example:

  fun test(steps: Map<String, Int>) {
      steps.map { it.key }.toSet()
  }

  fun test(steps: Map<String, Int>) {
      steps.keys
  }

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.

ReplaceMapKeysCallChainWithKeys

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 ID: ReplaceMapKeysCallChainWithKeys

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 ReplaceMapKeysCallChainWithKeys

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

IntelliJ IDEA 2026.2

Inspection Details
By default bundled with:	IntelliJ IDEA 2026.2, Qodana for JVM 2026.2,

Last modified: 30 June 2026