DontDowncastCollectionTypes.md

Pattern: Down-casting collection type

Issue: -

Description

Down-casting immutable types from kotlin.collections should be discouraged. The result of the downcast is platform specific and can lead to unexpected crashes. Prefer to use instead the toMutable<Type>() functions.

Example of incorrect code:

val list : List<Int> = getAList()
if (list is MutableList) {
    list.add(42)
}

(list as MutableList).add(42)

Example of correct code:

val list : List<Int> = getAList()
list.toMutableList().add(42)

Further Reading

• Detekt - DontDowncastCollectionTypes