Is there general advice if it is better to use var and immutable lists or val and mutable lists if a collection needs to be modified?
The concrete use case is: Storing listener references which can be added and removed.
(there is a similar question on Stackoverflow which I’m summarizing here)
Both approaches have different pros and cons. A mutable list in a val is usually more efficient, if you are modifying it often. An immutable list in a var on the other hand is safer, if it is accessible to the outside of your class/method, or you ever pass or return it somewhere else: with a mutable list, the outside code could modify the list. The consensus from Stackoverflow answers is, to use a var with an immutable list always is the safe choice.
So for your use case, handling a list of listeners, I’d assume that it isn’t changed often enough to be performance-critical and I’d use a var with an immutable list.
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Thank you for your reply!
I had equal considerations: The collection of listeners won’t be changed so often that this could lead to a performance issue; and if the list is accidantly exposed to the outside it is still immutable and safe.