Lazily coalesce Options in Scala

Question

I have several ways of calculating a value, in decreasing preference.

firstWay()
second() + way()
orA(thirdWay())

Each of these returns an Option. I want to "coalesce" these and get an Option which the the value returned by the first Some of these, or None if all returned None.

Of course, if firstWay() returns a Some, I shouldn't calculate the rest.

What is the most idiomatic (or at least reasonably readable) way to do this?

score 11 · Accepted Answer · answered Feb 18 '14 at 01:40

11

firstWay().orElse(second() + way()).orElse(orA(thirdWay()))

orElse's argument is lazily evaluated.

See the documentation.

answered Feb 18 '14 at 01:40

Karol S

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score 2 · Answer 2 · answered Feb 18 '14 at 10:12

2

If you have enough ways that Karol's answer becomes unwieldy, or don't know in advance how many:

val options: Stream[Option[A]] = ...
// in the example: firstWay() #:: (second() + way()) #:: orA(thirdWay())

options.foldLeft[Option[A]](None)(_.orElse(_))

answered Feb 18 '14 at 10:12

Alexey Romanov

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Lazily coalesce Options in Scala

2 Answers2