From: jeffz_2002@...
Date: 2007-01-03T13:55:08+09:00
Subject: Pickaxe question: "... on the way to true Ruby mastery."

Pickaxe has this code on page 374:

def once(*ids) # :nodoc:
  for id in ids
    module_eval <<-"end;"
    alias_method :__#{id.to_i}__, :#{id.to_s}
    private :__#{id.to_i}__
    def #{id.to_s}(*args, &block)
       (@__#{id.to_i}__ ||= [__#{id.to_i}__(*args, &block)])[0]
    end
end;
end
end

followed by "Understand this code, and you'll be well on the way to
true Ruby mastery."  I don't, so I'm not, but would like to, and then I
will (according to the book) - with some help.

I'm good up until the line (@__#{id.to_i}__ ||= [__#{id.to_i}__(*args,
&block)])[0]

Say the id.to_i was 42 ... then this reads: (@__42__ ||= [__42__(*args,
&block)])[ 0 ]

or: (@__42__ ||= [ return value from __42__ method call ] )[ 0 ]


Question: Why can't we just write

(@__42__ ||= return value from __42__ method call)

Why is the [0] necessary at all?

Thanks, (ps - a link to an in-depth explanation would be sufficient!)

Jeff