Kotlin - Making it mutable in foreach

Question

So I've come to learn that the it in my foreach loop is immutable - namely I get the error val cannot be reassigned.

results.forEach{
            val subGenreNames = subGenreNames(it.subGenres)
            it.subGenres = subGenreNames
}

However I want to be able to update its value after I pass it into my subGenreNames function.

How can I achieve this?

`it` is of my own type - `Song` - ahh, and yes, within that `subGenres` was set a val. I updated it to be a var and it worked. — userMod2, Oct 29 '19 at 01:25

score 0 · Answer 1 · answered Oct 29 '19 at 07:25

Are you sure you want to mutate subGenres rather than create new list with updated values? The more Kotlin way would be

val withSubGenreNames = results.map {
            it.copy(subGenres = subGenreNames(it.subGenres))
}

where copy is magical method if your it is data class.

This way you'd keep old list unchanged. You can read here why immutability is generally a good practice.

score 0 · Answer 2 · answered Oct 29 '19 at 08:18

0

Your quation was answered in the comments by @Egor, so I will just post the answer for you to resolve:

The it in the labda is immutable but the actual setter accesses inner field subGenres, which I guess is a val. Change subGenres to a var.

answered Oct 29 '19 at 08:18

Neo

2 Answers2