```val map = getMapOfDataFromOutside() val homeCou...

# getting-started

[Vitali Plagov]

val map = getMapOfDataFromOutside()
val homeCountry = map["Home Country"] ?: error("Data table is missing 'Home Country' entry or its key is incorrect")
val homeCity = map["Home City"] ?: error("Data table is missing 'Home City' entry or its key is incorrect")

Hi. I have this map and I handle the nullable value by a key with ?: error(…) . The error message is equal for all entries I’m retrieving except one parameter, so I want to extract this into a separate method to make code shorter:

val homeCountry = map["Home Country"] ?: throwAnErrorForKey("Home Country")
private fun throwAnErrorForKey(key: String) {
    error("Data table is missing '$key' entry or its key is incorrect")
}

With this code, the return type of the homeCountry is Any and not String.
How can I extract the ?: error() part properly?

[Ruckus]

Change the return type to Nothing

private fun throwAnErrorForKey(...): Nothing { ... }

[Vitali Plagov]

Thanks @Ruckus. Set the type to Nothing and it works now

[Vitali Plagov]

@Dorian the error() function is from a kotlin-stdlib. A shorthand for throw IllegalStateException().

[Ruckus]

If the message is always the same, except for the key, you could make a little helper function (@Dorian's answer might be a little over-engineered for this particular case):

fun Map<String, String>.getOrThrowError(key: String): String =
    get(key) ?: error("Data table is missing '$key' entry or its key is incorrect")

Then your usage would be

val map = getMapOfDataFromOutside()
val homeCountry = map.getOrThrowError("Home Country")
val homeCity = map.getOrThrowError("Home City")