if you really want to ensure the return type can y...

# announcements

[cdurham]

if you really want to ensure the return type can you use filterTo ?

[diesieben07]

Yes, and you should! This is exactly the thing for this use case.

[aphex]

I just tried that hahahah! The problem is, that filterTo requires a mutable map, of course

[cdurham]

uh, is HashMap not mutable?

[aphex]

Now I’m wishing for a .filterToType<HashMap<K,V> or something….

[diesieben07]

That cannot be reasonably implemented without reflection, which is slow, unreliable and ugly.

[diesieben07]

And that filterToType would still return a mutable map.

[diesieben07]

All that filter does, by the way, is call filterTo with a LinkedHashMap. So if you do val filtered: Map<K, V> = filterTo(HashMap()) { } you have the same effect.

[cdurham]

you said you wanted to ensure the return type as a HashMap using filterTo does that. if you really need you can cast it, although IMO you shouldn't need to know the concrete type in most scenarios

[diesieben07]

Don't cast the result of filter! That is not guaranteed to work and might crash with a newer version of Kotlin.

[cdurham]

you can cast the return of filterTo not filter nvm shouldn't be necessary

[diesieben07]

You don't need to cast the result of filterTo.

[diesieben07]

Yeah, it returns what you pass in.