Swapping two vars in scala

Question

Possible Duplicate:
Tuple parameter declaration and assignment oddity

In python I can do

>>> (a,b) = (1,2)
>>> (b,a) = (a,b)
>>> (a,b)
(2, 1)

But in scala:

Welcome to Scala version 2.8.1.final (OpenJDK Server VM, Java 1.6.0_20).
Type in expressions to have them evaluated.
Type :help for more information.

scala> var (a,b) = (1,2)
a: Int = 1
b: Int = 2

scala> (a,b)=(b,a)
<console>:1: error: ';' expected but '=' found.
       (a,b)=(b,a)
            ^

So while I can initialise vars as a tuple, I cannot assign them as a tuple. Any way to get around this, other than using a tmp var?

Possible duplicate? http://stackoverflow.com/questions/1624484/tuple-parameter-declaration-and-assignment-oddity http://stackoverflow.com/questions/6196678/is-it-possible-to-have-tuple-assignment-to-variables-in-scala — Kipton Barros, Jul 10 '11 at 16:05

score 15 · Answer 1 · answered Jul 10 '11 at 20:37

15

This is Scala 2.9.0.1

scala> val pair = (1,2)
pair: (Int,Int) = (1,2)

scala> val swappedPair = pair.swap
swappedPair: (Int,Int) = (2,1)

The method swap produces another tuple instead of changing the old one and I don't know if it has been there in Scala 2.8.1.

answered Jul 10 '11 at 20:37

agilesteel

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4

yes, it is there in 2.8, but this only returns a swapped tuple. So the problem of swapping the ids of the vars is not solved. – georg Jul 10 '11 at 21:20

score 8 · Accepted Answer · edited May 23 '17 at 11:54

8

Unfortunately, there's no simple way. The expression (a,b) constructs an immutable object of type Tuple[Int, Int]. Within this tuple, the identities of a and b as mutable vars are lost. Two previous questions may give a little more information:

Tuple parameter declaration and assignment oddity

Is it possible to have tuple assignment to variables in Scala?

edited May 23 '17 at 11:54

Community

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answered Jul 10 '11 at 16:11

Kipton Barros

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Swapping two vars in scala

2 Answers2