From: David Vallner <david@...>
Date: 2006-01-12T20:06:18+09:00
Subject: Re: Newbie question about multiple assignments

To your why, another why: why do you need to use multiple parallel  
assignments in one statement? That said, parallel assignments are somewhat  
known to be a rather messy bit of syntax I'm apparently not as savvy with  
as I thought, since I can't make heads or tails of what is really  
happening.

My personal tip woukd be that the assignments are associative  
right-to-left, and only the leftmost assignment is evaluated as a parallel  
one.

What probably happens is broken down into simpler statements:

a = a, b # a == [1, 2]
a, b = b, *a # a ==2, b==1

where the return value of the expression is the rvalue.

So the end values are what you expect, just the return value of the  
expression isn't.

Hint: it's easy to avoid obscure syntax, so do that if possible. Noone  
really admires godawful one-liners from hell in code he expects to  
understand a week after writing it, even if there is a certain charm to  
getting things done with them ;)

Also, parallel assignment syntax is undergoing certain subtle, but  
significant changes that seem to resolve some of the ambiguity - you might  
want to look on one of the webpages that summarize changes in Ruby 1.9.

David Vallner

On Thu, 12 Jan 2006 11:24:45 +0100, Alex <AlexAfrasinei@yahoo.com> wrote:

>
> irb(main):091:0> a=1
> => 1
> irb(main):092:0> b=2
> => 2
> irb(main):093:0> a,b=b,a
> => [2, 1]
> irb(main):094:0> a=1
> => 1
> irb(main):095:0> b=2
> => 2
> irb(main):096:0> a, b = b, a = a, b
> => [2, 1, 2]                           <-- Why?
>
> What is the order for the assignments
>