Scala Tuple Deconstruction

I am new to Scala, and ran across a small hiccup that has been annoying me.

Initializing two vars in parallel works great: var (x,y) = (1,2)

However I can't find a way to assign new values in parallel: (x,y) = (x+y,y-x) //invalid syntax

I end up writing something like this: val xtmp = x+y; y = x-y; x = xtmp

I realize writing functional code is one way of a开发者_高级运维voiding this, but there are certain situations where vars just make more sense.

I have two questions:

1) Is there a better way of doing this? Am I missing something?

2) What is the reason for not allowing true parallel assignment?

Unfortunately, you cannot do multiple assignments in Scala. But you may use tuples, if they fit your problem:

scala> var xy = (1,2)
xy: (Int, Int) = (1,2)

scala> xy = (xy._1 + xy._2, xy._2 - xy._1)
xy: (Int, Int) = (3,1)

This way, xy is one tuple with two values. The first value can be accessed using xy._1, the second one using xy._2.

Scala has 2 types of variables: vals and vars. Vals are similar to Java's final variables, so as far as I understand from what you're asking, the only way to assign new values in parallel to vals is by:

scala> val (x, y) = (1, 2);

or

scala> val s = (3, 4);
s: (Int, Int) = (3,4)

scala> s._1
res1: Int = 3

scala> s._2
res2: Int = 4