From: dblack@...
Date: 2006-03-17T05:28:41+09:00
Subject: Re: specify a mandatory block parameter

Hi --

On Fri, 17 Mar 2006, Shea Martin wrote:

> I think I know the answer to this already, but...
>
> Is there a what to make a block parameter mandatory?
>
> <code>
> def no_block( p_str )
> 	puts "#{p_str}"

I believe that in every case, that's exactly equivalent to:

   puts p_str

because #{...} interpolates the results of a to_s call, and puts also
calls to_s.

> end
>
> def block( &p_block )
> 	puts "#{p_block}"
> end
>
> no_block #this will cause an exception
> block #this doesn't, but is still missing parameter?
> </code>
>
> I know, I could just raise my own exception if p_block == nil, just wondering 
> why the difference?  Or am I wrong?

The block is really in its own category as a semantic (and syntactic)
thing.  You can hook into it in the arglist, but it's really a
separate construct -- more on the logical level of the arglist itself,
rather than a particular argument.

You can test for the presence of a block with block_given? or its
synonym, iterator?


David

-- 
David A. Black (dblack@wobblini.net)
Ruby Power and Light, LLC (http://www.rubypowerandlight.com)

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