Is there a Kotlin convenience function that allows...

# getting-started

[Klitos Kyriacou]

Is there a Kotlin convenience function that allows me to combine multiple Iterables into a single Iterable?

In other words, can I do something like this:

(list1 + list2).firstOrNull { it.matches(something) }

but without eagerly iterating the lists and creating a new list from them?

In other words, exactly like Guava's FluentIterable.concat(list1, list2) but more Kotlin-idiomatic?

[Youssef Shoaib [MOD]]

Use a sequence:

sequence {
  yieldAll(list1)
  yieldAll(list2)
}.firstOrNull {...}

[Klitos Kyriacou]

Thanks. sequenceOf(list1, list2).flatten() is even a little bit shorter. If I wanted the exact behaviour of FluentIterable.concat I would have to add .asIterable(). It's just a little bit disappointing that sequenceOf(list, list2).flatten().asIterable() is longer than FluentIterable.concat(list1, list2) but most of the time I can take it directly as a Sequence, so I can omit the .asIterable().

[Youssef Shoaib [MOD]]

Even better would maybe be defining `plus`for sequences and then just doing (list1.asSequence() + list2).asIterable()

[Klitos Kyriacou]

That's nice too (though the asymmetry of calling asSequence on only one of the lists makes the code less elegant)

[Youssef Shoaib [MOD]]

You could call it on both as well, but it'll just be a bit redundant. The `flatten`solution is neat though, even if it technically results in like one extra sequence being created lol

[Klitos Kyriacou]

The plus method is implemented using flatten anyway.

[Youssef Shoaib [MOD]]

Oh I didn't even realise that was the underlying implementation lol! Yeah definitely go with the flatten solution then

[nkiesel]

We have a flatMap as convenience for .map{}.flatten(), so having a flatSequenceOf might be nice