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
– Sweeper, Commented Sep 29, 2021 at 9:10
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
– Kratos, Commented Sep 29, 2021 at 9:19
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
– Sweeper, Commented Sep 29, 2021 at 9:22
Can you please write that down, how would it look? bundle. applyWithUserParameters....? — Kratos
– Kratos, Commented Sep 29, 2021 at 9:27

Sweeper · Accepted Answer · 2021-09-29 10:15:11Z

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, 2021 at 10:15

answered Sep 29, 2021 at 9:42

Sweeper

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1 Comment

Kratos Over a year ago

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

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