vararg and extension function in kotlin

Question

I am trying to write extension function in kotlin. I came almost to the end but one simple thing stopped me. Code goes like this:

fun Bundle.applyWithUserParameters(vararg functionList: () -> Unit = null): Bundle = Bundle().apply {
for (method in functionList)
    method()
FirebaseAnalyticsHelper.clientRepository.getClientData()?.clientID?.let {
    putInt(
        FirebaseAnalyticsHelper.KEY_USER_ID, it
    )
}
}

null is underlined and it says: "Null can not be a value of a non-null type Array<out () -> Unit>"

Is there any way to fix this or I am unable to use vararg at all in this case? Thanks

You seem to be setting the default value of the varargs parameter to null. That doesn't make much sense. Why do you want to do that? — Sweeper, Sep 29 '21 at 09:10
Because in some cases I will send 2,3,4 functions as arguments and in some cases, I will send zero arguments to applyWithUserParameters — Kratos, Sep 29 '21 at 09:19
So...? Why does that mean you need `= null`? A vararg, by itself, without a default value, can take 0 or more arguments. How about removing `= null`? — Sweeper, Sep 29 '21 at 09:22
Can you please write that down, how would it look? bundle. applyWithUserParameters....? — Kratos, Sep 29 '21 at 09:27
When I call this extension function from my code with zero arguments (in some other class). — Kratos, Sep 29 '21 at 09:29
Let us [continue this discussion in chat](https://chat.stackoverflow.com/rooms/237630/discussion-between-sweeper-and-kratos). — Sweeper, Sep 29 '21 at 09:30

Sweeper · Accepted Answer · 2021-09-29T10:15:11.753

3

You seem to be trying to set the default value of the varargs parameter to null. This is not needed. Varargs can take 0 parameters, even without a default value.

fun Bundle.applyWithUserParameters(vararg functionList: () -> Unit): Bundle = 
    Bundle().apply {
        for (method in functionList)
            method()
        FirebaseAnalyticsHelper.clientRepository.getClientData()?.clientID?.let {
            putInt(
                FirebaseAnalyticsHelper.KEY_USER_ID, it
            )
       }
    }

This works:

someBundle.applyWithUserParameters()

edited Sep 29 '21 at 10:15

answered Sep 29 '21 at 09:42

Sweeper

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True that! I didn't know the fact that vararg takes 0 parameters even without default value when you write it with empty brackets. Thanks for your help – Kratos Sep 29 '21 at 09:51

vararg and extension function in kotlin

1 Answers1