From: Rich Morin <rdm@...>
Date: 2007-05-25T19:13:41+09:00
Subject: Replacement idiom for "list_or_nil.to_a"?

Many scripting languages, including Ruby, will "do nothing
gracefully" when asked to iterate through an empty list.
That is, they iterate NO times.

However, many Ruby methods do not return empty lists when
nothing is found.  Instead, they return nil.  This means
that idioms such as:

  list_or_nil.each do |value|
    ...
  end

will fail.  As a workaround, I've been using this idiom:

  list_or_nil.to_a.each do |value|
    ...
  end


However, I gather that this will soon be deprecated:

  http://www.megasolutions.net/ruby/to_a-68350.aspx

This page suggests putting the list in brackets:

  [list_or_nil]

but this doesn't solve MY problem:

  >> list_or_nil=nil
  => nil
  >> [list_or_nil]
  => [nil]

because the loop will now run once with the value nil.
I really dislike having to wrap the iteration block in
an "if" block:

  if list_or_nil
    list_or_nil.each do |value|
      ...
    end
  end

and this is only marginally better:

  list_or_nil.each do |value|
    ...
  end if list_or_nil


I suppose I could define my own to_a method for nil,
but that seems a bit questionable, as well.  So, is
there a Better Way To Do It?

-r
-- 
http://www.cfcl.com/rdm            Rich Morin
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