From: Robert Klemme <bob.news@...>
Date: 2006-01-11T23:58:04+09:00
Subject: Re: on parallel assignment

Christer Nilsson wrote:
> The parallel assignment syntax
> [a,b] = [c,d]   is not allowed

The left side is an array constructor.  In other words: take value of a
and value of b and create a two element array.  There is no assignment
here.  You cannot create an array on the left side of an assignment and
try to assign to it:

>> []=[1,2]
SyntaxError: compile error
(irb):38: syntax error
[]=[1,2]
   ^
        from (irb):38
        from ���:0
>> Array.new = [1,2,3]
NoMethodError: undefined method `new=' for Array:Class
        from (irb):39
        from ���:0
>> (Array.new) = [1,2,3]
SyntaxError: compile error
(irb):40: syntax error
(Array.new) = [1,2,3]
             ^
        from (irb):40
        from ���:0

> I have to write
> a, b = [c,d]

I prefer

>> a,b=1,2
=> [1, 2]
>> a
=> 1
>> b
=> 2

> Going deeper
> [a, [b, c]] = [1, [2, 3]]   is not allowed
>
> I have to write
> a, (b, c) = [1, [2, 3]]

You can as well do

>> a,(b,c)=1,[2,3]
=> [1, [2, 3]]
>> a
=> 1
>> b
=> 2
>> c
=> 3

The outermost array is implicit but you must create nested arrays
explicitely.

> I'm sure there is a good reason these constructs are disallowed.
> Can somebody enlighten me?

Hope so...

Kind regards

    robert