what would be a nice way to implement a keyTypeMap...

# getting-started

[Michael de Kaste]

what would be a nice way to implement a keyTypeMap.
Something like Map<KClass<out T>, SomeType<T>>
currently we are filtering from a list in multiple factories which is an O(factories * N) problem. Ideally I just want to request a class type from a map and get the correct implementation

[Tobias Berger]

I suggest writing some (non-Map) type that uses some regular Map in the background and handles the type casting for you.
you could even write reified overloads of get and set, so you wouldn't even need to put the class object in the arguments (depending on your use case).
A real Map implementation will probably not work, at least not with the default get and put methods, because you can't override the interface methods with one that requires generics.

Here is an example implementation: https://pl.kotl.in/A2tG9y92U

[Michael de Kaste]

Looks great Tobias! The solution was indeed a simple wrapper. I had my mind set on a map implementation

[ephemient]

the Map interface can't express this. stdlib itself has what is effectively a typed map: kotlin.coroutines.CoroutineContext associates from Key<Element> to Element. there's a few other projects out there like https://github.com/broo2s/typedmap. but if you just want a class->instance map, something simple like that example is fine.

[Joffrey]

You could also look at how the coroutine context map is implemented. It's basically a typed heterogeneous map like you're looking for. Maybe slightly more complicated than the example here

[ephemient]

I don't think CoroutineContext as a typed map is a reasonable thing to copy unless you're building something just like it, because there's no explicit Map; it's built up from + and composition of various `Element`s each of which will handle get of its own key or delegate to the next context