DoubleMutabilityForCollection.md

Pattern: Use of var when declaring mutable collection

Issue: -

Description

Using var when declaring a mutable collection leads to double mutability. Consider instead declaring your variable with val or switching your declaration to use an immutable type.

Example of incorrect code:

var myList = mutableListOf(1,2,3)
var mySet = mutableSetOf(1,2,3)
var myMap = mutableMapOf("answer" to 42)

Example of correct code:

// Use val
val myList = mutableListOf(1,2,3)
val mySet = mutableSetOf(1,2,3)
val myMap = mutableMapOf("answer" to 42)

// Use immutable types
var myList = listOf(1,2,3)
var mySet = setOf(1,2,3)
var myMap = mapOf("answer" to 42)

Further Reading

• Detekt - DoubleMutabilityForCollection