Why can’t I pass a value of type `Map<String, S...

# announcements

[ribesg]

Why can’t I pass a value of type Map<String, String?> for a parameter requiring type Map<Any?, *>?

[Big Chungus]

String extends Any whereas String? extends Any?

[Big Chungus]

In short Any does NOT extend Any?

[ribesg]

I can’t pass Map<String?, String?> either

[Big Chungus]

Ah

[Big Chungus]

Your parameter def needs to be Map<out Any?, *>

[ribesg]

Well it’s not my function

[Big Chungus]

Otherwise it'll require you to cast to Any, rather than allowing extensions

[Big Chungus]

Then cast your map to required type

[ribesg]

Yeah a forced cast should not cause any problem in this specific case

[ribesg]

The function I called is defined as

@kotlinx.cinterop.ObjCMethod public open external fun setMetadata(metadata: kotlin.collections.Map<kotlin.Any?, *>): kotlin.Unit

[Big Chungus]

It's an open function. I'd override it with modified def

[Big Chungus]

See if the compiler complains

[thana]

generics are invariant i.e. String is Any but List<String> !is List<Any>

[ribesg]

I’m calling this only once so I’ll go with a forced cast

[streetsofboston]

@thana A List<String> is a List<Any>, since list is defined as List<out T>

[streetsofboston]

But for a Map, the key is an invariant, not a covariant: Map<K, out V>

[thana]

Oh yes, you are right i forgot about declaration-site varrance in kotlin and just copied the standard java example over

[streetsofboston]

(if it weren’t for the keys and entries properties, Map could have been `Map<in K, out V>`….)

[louiscad]

Answering the initial question: Because if you pass it to Map<Any?, *>, you would then be able to put anything in the map, be it mutable under the hood.