From: "David A. Black" <dblack@...>
Date: 2010-04-15T08:51:21+09:00
Subject: Re: I thought spaces didn't matter around operators

Hi --

On Wed, 14 Apr 2010, Sarah Allen wrote:

> David A. Black wrote:
>> Here's another interesting space/non-space case:
>>
>>   >> def m(*args); "hi"; end
>>    => nil
>>   >> m *10
>>    => "hi"
>>   >> m * 10
>>    => "hihihihihihihihihihi"
>>
>> In m *10 the * is the unary *, while in m * 10 it's the infix
>> operator/method *.
>>
>>
>> David
>
> And what, may I ask, it the unary * operator?  Is it what I've heard
> Rubyists call the "splat" operator that you use in var args?  How and
> why would you override it?

It is indeed what people call the "splat" operator, though I've never
found that name very expressive. I think of it as the unar[r]ay
operator (that's unary unarray :-) It does an "unarray" operation in
the sense that it can turn an array into a bare list, in a method
call.

You can't define it directly (I believe that's true in 1.9 as well as
earlier versions), but you can affect what it does via the #to_a
method:

   o = Object.new
   def o.to_a; [1,2,3]; end
   a = *o
   p a    # [1,2,3]

As for the why: I don't think you'd often define #to_a just to get *
behavior. It's more of an extra thing you get in cases where you need
#to_a anyway.


David

-- 
David A. Black
Senior Developer, Cyrus Innovation Inc.
THE COMPLEAT RUBYIST, Ruby training with Black/Brown/McAnally!
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