Question

I’ve searched for a half-hour, and still cannot figure it out.

In SIP: Modularizing Language Features there are a number of features which will require explicit “enabling” in Scala 2.10 (import language.feature).
Amongst them there is postfixOps, to which I just cannot find a reference anywhere. What exactly does this feature allow?

Answer 1

It allows you to use operator syntax in postfix position. For example

List(1,2,3) tail

rather than

List(1,2,3).tail

In this harmless example it is not a problem, but it can lead to ambiguities. This will not compile:

val appender:List[Int] => List[Int] = List(1,2,3) ::: //add ; here
List(3,4,5).foreach {println}

And the error message is not very helpful:

    value ::: is not a member of Unit

It tries to call the ::: method on the result of the foreach call, which is of type Unit. This is likely not what the programmer intended. To get the correct result, you need to insert a semicolon after the first line.