What does a "?" symbol (question mark) mean in Scala?

Question

I meet some scala code with "?" but do not know what it mean in scala, could anyone explain it to me ? Thanks.

And here's one example

 def getJobId(conf: Configuration): String = ?(conf.get("scoobi.jobid")).getOrElse(sys.error("Scoobi job id not set."))

Can you give an example? The "?" could be part of a method name, class name, or something else. It's not a standard operator in Scala. — Jesper
– Jesper, Commented Apr 6, 2012 at 6:58
is it just me or is the "?" helper method in this case utterly pointless? The same result, with fewer characters and, IMHO, more clarity, is obtained with standard, conf.get("foo") getOrElse sys.error("bar") — virtualeyes
– virtualeyes, Commented Apr 6, 2012 at 9:42
@virtualeyes Option.apply(x) converts null to None. So If conf.get("foo") doesn't return an Option, but might return null, then this is done to convert the possible null to None (see Christian's answer). — Jesper
– Jesper, Commented Apr 6, 2012 at 11:14
Assumed the get in this case was on an Option, but looking again, not the case. "import Option.{apply => ?}" is, btw, really quite awesome ;-) — virtualeyes
– virtualeyes, Commented Apr 6, 2012 at 18:41

Christian · Accepted Answer · 2012-04-06 08:29:02Z

For me it looks like the apply method of Option. Is there somewhere the following import statement in the code:

import Option.{apply => ?}

This means apply is imported as ?. From the doc of Option.apply:

An Option factory which creates Some(x) if the argument is not null,
and None if it is null.

The whole statement means then:

if conf.get("scoobi.jobid") is not equal null, assign this string, otherwise assign the string sys.error("Scoobi job id not set.") returns

Thanks, you are right. There's an import statement ahead "import Option.{apply => ?}"

Community · Accepted Answer · 2017-05-23 10:28:21Z

It's just a legal character, just like "abcd..."

scala> def ?(i: Int) = i > 2 $qmark: (i: Int)Boolean scala> val a_? = ?(3) a_?: Boolean = true

UPD: See Valid identifier characters in Scala , Scala method and values names

UPD2: In the example "?" could be function, method of this or just some object with apply method. It probably returns Option[String].

2 Answers 2