For curiosity, why extension of array return list?...

# stdlib

[shusek]

For curiosity, why extension of array return list? It does not make sense to me.
intArrayOf(1,2,3).filter { it > 1} = List<Int>

[diego-gomez-olvera]

I guess that arrays are there for Java interop and for cases where its efficiency is really needed. http://www.informit.com/articles/article.aspx?p=2861454&amp;seqNum=3

[diego-gomez-olvera]

filter performs a new allocation, so it is not really minimizing the memory footprint anyways

[hho]

Well, you don't know up front how many of the array elements will match the predicate – so you can't allocate an array up front. So you need the list allocation anyway, and then you can just return it as well (making IntArray.filter {…} line up nicely with Collection.filter {…}).

If you want an IntArray out, you'll have to call .toIntArray() on the resulting list – and yes, this will make another copy of the data.

[shusek]

Okay, now I get it. It looks a bit weird but make sense.