Koltin: "abstract member cannot be accessed directly" when using delegation ("by" keyword)

user_10231266 0
Viewed 195

This is the sample code:

class PurchaseHistory: MutableList<PurchaseInfo> by mutableListOf() {
    override fun add(element: PurchaseInfo): Boolean {
        // ... some code
        return super.add(element)
    }
}

However, I am getting abstract member cannot be accessed directly. When I use original method from outside the class, I doesn't encounter any issues, but why can't I do the same thing from inside of it?

kotlin overriding delegates
2 Answers

I believe you get this error because the add method you're trying to call is not really in PurchaseHistory's super class.

To do what you want, you can keep a handle to the object you are delegating to. For instance, you can store it as a property:

class PurchaseHistory(
    private val backingList: MutableList<PurchaseInfo> = mutableListOf()
): MutableList<PurchaseInfo> by backingList {
    override fun add(element: PurchaseInfo): Boolean {
        // ... some code
        return backingList.add(element)
    }
}

Another option is to directly extend an implementation of MutableList (such as ArrayList) instead of implementing by delegation, but that might not be an option for you.

user_15408180

You are trying to call method from interface MutableList which is not defined.

Just make ArrayList supper of your class, and you should have good result:

class PurchaseHistory: ArrayList<PurchaseInfo>() {

    override fun add(element: Int): Boolean {
        // ... some code
        return super.add(element)
    }
}
user_68449300
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