Immutability

Mobius.kt requires most objects to be immutable, including the Model, Event, and Effect objects. Without this constraint Mobius does not work.

An object is immutable if it and all objects it refers to do not have mutable fields. Mutable fields are only safe if they do not change during the objects existence.

Beware of arrays

Arrays are mutable so having a val myarray: Array<Int> or final Array<Int> myArray = ... only applies to the field and not the array values.

For data structures, ensure you're using an Immutable variant or create a copy from the original source. For example, prefer ImmutableList from kotlinx.collections.immutable over the standard List type. If that is not possible, use myList.toList() to create a copy before storing the list in an object.