From: 7stud -- <bbxx789_05ss@...>
Date: 2009-07-23T20:32:58+09:00
Subject: Re: Ruby "star".... what's it?

Max Williams wrote:
> 
> 7stud - am i right in thinking that if i do this
> 
> a, b = 1, 2
> 
> ruby is automatically starring just the right side of the expression, 
> under the hood?  eg
> 

In pickaxe2, p. 91, the rule is:
----
When an assignment has more than one lvalue, the assignment expression 
returns an array of the rvalues.  Testing that out:
----

result = (x, y = [1], [2, 3])
p result

So I guess you could say "ruby is automatically starring the right hand 
side of a parallel assignment if there is more than one lvalue, and the 
resulting array is the value of the entire expression.

And I guess this wasn't a very good example:

x, y, z = *[1, 2, 3]
puts x, y, z

--output:--
1
2
3


Because you can eliminate the star and get the same output:

x, y, z = [1, 2, 3]
p x
p y
p z

--output:--
1
2
3


But this is where the star makes a difference:

x, y, z = 1, [2, 3]
p x
p y
p z

--output:--
1
[2, 3]
nil


x, y, z = 1, *[2, 3]
p x
p y
p z

--output:--
1
2
3

(This applies to ruby 1.8.  See David Black's post for 1.9 behavior.)
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