Idiomatic way of treating Option[Boolean]

Question

In my Scala program, I am receiving some JSON.

One of the fields is an optional Boolean. If the field is missing, or if its value is false, I would like to return None. If its value is true, I would like to return Some(true).

SInce this is equivalent to converting Some(false) into None, I have defined the following function:

def boolmap(ob: Option[Boolean]) = if(ob == Some(false)) None else ob

It works, but it doesn't seem to be very idiomatic. Is there anything more elegant?

Since you are reducing a triadic condition to a dual condition, IMO idiomatic would be to produce a plain boolean (`getOrElse(false)`) and drop the `Option` — 0__, Jun 18 '13 at 22:30
@0__ The thing is having the Option is quite handy for some processing I have to do later on. — Eduardo, Jun 18 '13 at 22:31
Could you not use `ob.isDefined` to get the underlying boolean value? — Jason D, Feb 24 '15 at 15:45

score 22 · Accepted Answer · answered Jun 18 '13 at 22:18

22

This is ob.filter(identity). I'm not sure whether that's clearer, but it's shorter.

answered Jun 18 '13 at 22:18

Rex Kerr

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Thanks! I have also found `for(x <- ob if x) yield x` – Eduardo Jun 18 '13 at 22:39
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@Eduardo - Indeed. There's also `ob.filterNot(! _)`, `ob.find(identity)`, `ob.collect{ case true => true }`, and various others. You can also write `x=>x` in place of `identity`. – Rex Kerr Jun 18 '13 at 22:58

Marcel Molina · Answer 2 · 2013-06-18T23:20:24.130

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I agree with others that you might as well just return true or false since you aren't differentiating between the attribute not being there at all, being null or being false.

If you just returned Boolean you could do it this way:

scala> Some(true) exists { _ == true }
res0: true

scala> Some(false) exists { _ == true }
res1: Boolean = false

scala> None exists { _ == true }
res2: Boolean = false

If you insist on returning Option[Boolean] a pattern match would be more idiomatic:

ob match { 
  case Some(true) => Some(true) 
  case _          => None 
}

You could also use collect but in this case it would look IMO weird:

obj collect { case true => true }

edited Jun 18 '13 at 23:20

answered Jun 18 '13 at 23:13

Marcel Molina

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Instead of `exists { _ == true }` it is more sensible to write `exists(identity)` or `contains(true)`. Comparing bool to true is frowned upon by many programmers [Is it bad to explicitly compare against boolean constants e.g. if (b == false) in Java](http://stackoverflow.com/questions/2661110/is-it-bad-to-explicitly-compare-against-boolean-constants-e-g-if-b-false-i). – Suma Apr 06 '15 at 15:27

Idiomatic way of treating Option[Boolean]

2 Answers2