From: John Lane <ruby-forum@...>
Date: 2010-04-15T19:17:49+09:00
Subject: Blocks and local variable creation

Hello,

I have a simple method:

def rights_for_item (rights_hash, item)
   rights_hash.each { |k,v| (rights ||= []) << k if v.include? item }
   rights
end

This does not work because "rights" is created local to the block on
"rights_hash.each" instead of local to the method itself. This makes the
statement returning the value of "rights" to fail because there is no
method local variable called "rights".

I can do this instead

def rights_for_item (rights_hash, item)
   rights = Array.new
   rights_hash.each { |k,v| rights << k if v.include? item }
   rights
end

The problem is this returns an empty array rather than nil if no matches
are found. So I do this:

def rights_for_item (rights_hash, item)
   rights = Array.new
   rights_hash.each { |k,v| rights << k if v.include? item }
   rights.empty? ? rights : nil
end

But I don't think it is good idiomatic ruby code. Is there a better way
to write this type of thing ?
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