Extending Scala’s arrow notation for pairs

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Question Description

Scala, in Predef, defines support for -> and (here cleaned up a bit):

final class ArrowAssoc[A](val __leftOfArrow: A) extends AnyVal {    
    def -> [B](y: B): Tuple2[A, B] = Tuple2(__leftOfArrow, y)
    def →[B](y: B): Tuple2[A, B] = ->(y)

This conveniently allows you to create pairs using an arrow notation instead of the plain tuple syntax:

scala> "foo" → 42
res0: (String, Int) = (foo,42)

This arrow syntax can easily be extended with a type definition and an extractor (here only is shown):

type →[A, B] = (A, B)
object → { def unapply[A, B](t: (A, B)) = Some(t) }

This allows you to write things like:

"a" → 42 match { case a → b ⇒ println(s"found `$a` and `$b`") }


def foo[A, B](t: A → B) = ???

I am wondering if there any reason Scala doesn’t define those as well in its standard library. Are there any downsides to these definitions?

Practice As Follows

Here is one downside. Being able to do both

def foo[A, B](t: A -> B) = ???


def foo[A, B](t: A => B) = ???

would be confusing. If the types don’t line up, the compiler would catch it of course. However, only a experienced Scala programmer would understand the error message quickly.


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