Hi, small question. Is there a way to pattern match a lambda that receives a Map<K,V>. For exa...

# getting-started

[Lisandro Di Meo]

Hi, small question. Is there a way to pattern match a lambda that receives a Map<K,V>. For example:

onSomething { (key,value) : Map<K,V> -> ... }

[CLOVIS]

It's not a pattern match, it's just destructuration:

mapOf(
    "1" to 1,
    "2" to 2,
).forEach { (key, value) ->
    println("$key → $value")
}

Pattern matching implies some kind of conditional, it's not the case in Kotlin

[CLOVIS]

It also works with regular for loops:

val map = mapOf(…)

for ((key, value) in map) {
    …
}

https://kotlinlang.org/docs/destructuring-declarations.html

[Lisandro Di Meo]

Yes, I thought that should work

Destructuring declaration initializer of type Map<String, Boolean>! must have a 'component2()' function

[CLOVIS]

Ah, you have the wrong Map , you're using java.util.Map but you should be using kotlin.Map

[CLOVIS]

The ! in the type is a platform type (https://kotlinlang.org/docs/java-to-kotlin-nullability-guide.html#platform-types), it means you're using a type that comes from some other language (in your case, Java) which has missing information

[Lisandro Di Meo]

I thing the case is that this is a Map<K, out V>

[Lisandro Di Meo]

Oh

[Lisandro Di Meo]

damn, I cannot change it since it cames from a library 😅

[CLOVIS]

You should be able to cast it, the Kotlin Map is an alias for the Java one

[CLOVIS]

by manually casting it you tell the compiler that you yourself have checked for nullability

[Lisandro Di Meo]

In destructuring-declarations I found the following that worked:

aMap.mapValues { (aMapKey, aMapValue) ->
    ...
}

[Lisandro Di Meo]

Thanks 😄

[Joffrey]

Yeah you were actually trying to destructure the map itself instead of individual entries, that was your issue

[Lisandro Di Meo]

Yeah, silly me 😆