Hello. Can anyone explain to me, why some simle fu...

# announcements

[Serhiy Fedusov]

Hello.
Can anyone explain to me, why some simle functions on Iterable return list and not Iterable subtype it was applied to?
For example:

inline fun <T> Iterable<T>.filter(
    predicate: (T) -> Boolean
) : List<T>

If I chain multiple functions, say, using Set, it is simetimes uncomfortable to call toSet() each time the list is returned.

[louiscad]

Try to write one, and you'll see it's impossible as you can't predict how to make a new instance of that subtype.

[Serhiy Fedusov]

You probably can using reflection

[louiscad]

You can write one for Set<T> though

[louiscad]

It cannot work in all cases, and that'd have bad implications like performance by default, especially on Android, and wouldn't work on #C3SGXARS6 or #C0B8L3U69

[Ruckus]

Also, many of them have a to alternative (e.g. mapTo(mutableSetOf()) { ... })

[Serhiy Fedusov]

Brilliant. I somehow missed this feature. Thanks a lot for that