In Scala, how do I assign the tuple values to variables in a binary operation of Map?

Question

Possible Duplicate:
Tuple Unpacking in Map Operations

Lets say that I have the following Map[Int,Double]:

scala> map
res19: scala.collection.immutable.Map[Int,Double] = Map(1 -> 1.1, 2 -> 2.2)

I can run the following foldLeft on it:

scala> map.foldLeft("A")((initVal,x:(Int,Double)) => initVal + x._1)
res20: java.lang.String = A12

But I can't find a way to assign the tuple's values to named variables:

scala> map.foldLeft("A")((init,x:(a:Int,b:Double)) => init + x.a)
<console>:1: error: ')' expected but ':' found.
   map.foldLeft("A")((init,x:(a:Int,b:Double)) => init + x.a)
                               ^

Can this even be done?

score 7 · Accepted Answer · answered Oct 16 '12 at 23:33

7

You could use case

map.foldLeft("A") {case (init, (a,b)) => init + a}

answered Oct 16 '12 at 23:33

Ratan Sebastian

1,892
14
23

very cool. So what's the official name of this technique? So I can read on it. – Armin Oct 16 '12 at 23:43
I think it's officially called a destructuring bind. [This article](http://daily-scala.blogspot.com/2010/03/functions-using-case-statements.html) gives a little insight into how it's used here. – Ratan Sebastian Oct 16 '12 at 23:49
4

It's a form of pattern matching. – Jesper Oct 17 '12 at 05:46

In Scala, how do I assign the tuple values to variables in a binary operation of Map?

1 Answers1