```interface Store { val users: List<String...

# getting-started

[ursus]

interface Store {
    val users: List<String>
}

class StoreImpl : Store {
    private val mutableUsers = mutableListOf<String>()

    override val users: List<String>
        get() = mutableUsers

    fun addUser(name: String) {
        mutableUsers += name
    }
}

can I use explicit backing fields here somehow? i.e. when the property is defined on the interface

[Youssef Shoaib [MOD]]

I think it's just:

class StoreImpl : Store {
  override val users: List<String>
    field = mutableListOf()

  fun addUser(name: String) {
    users += name
  }
}

[Youssef Shoaib [MOD]]

I believe there's an IDE action that does this? If not, there definitely should be!

[ursus]

it complains about the proeprty nit being final

[ephemient]

final override val users: List<String>

[Youssef Shoaib [MOD]]

It seems to work just fine on the playground even without final

[loke]

@Youssef Shoaib [MOD] won't that recreate the list for every call to addUser ? I.e. it won't actually mutate the list because the exposed type is just List .

[Youssef Shoaib [MOD]]

I believe MutableList.plusAssign specifically calls .add. you can also call .add yourself

[loke]

@Youssef Shoaib [MOD] right, but in this case, users is declared as List, not MutableList.

[ursus]

no its mutable list, thats the whole point of the feature

[Youssef Shoaib [MOD]]

It's also a val, so += wouldn't work!
The whole point is we're using the new explicit backing field feature, which lets you access the real type of the field inside the class, but hide it from the outside

[ursus]

btw the final getting grayed out is IDE being old? (latest AS)