From: John Lane <ruby-forum@...>
Date: 2010-04-16T18:21:22+09:00
Subject: Re: Blocks and local variable creation

Robert Dober wrote:

> I do not reallly understand why you want nil, instead of [], but apart
> of this I would do
> select{|_,v| v.include? item}.map(&:first)
> 
> or if you insist
> 
> inject( nil ){ |r,(k,v)|  v.include?( item ) ? (r||[]) << k : r }

Can you please explain the line:
> select{|_,v| v.include? item}.map(&:first)

I've never seen the _ before where I would expect a variable. I also 
don't understand (&:first) on the call to map.

The reason I was returning nil was so I can the write code like this:

rights_held = rights_for_item (rights_hash, item)
perform_something_with_rights unless rights_hash.nil?

perhaps I should change that thought process to this:

rights_held = rights_for_item (rights_hash, item)
perform_something_with_rights unless rights_hash.empty?

I had thought use of nil was the right way but I'm learning so I'm happy 
to be convinced otherwise...
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