From: Robert Klemme <shortcutter@...>
Date: 2007-05-25T21:00:09+09:00
Subject: Re: Replacement idiom for "list_or_nil.to_a"?

On 25.05.2007 12:13, Rich Morin wrote:
> 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?

Probably.  How do you like

list_or_nil and list_or_nil.each do |x|
   ...
end

Or

irb(main):001:0> class NilClass
irb(main):002:1> def each; self; end
irb(main):003:1> include Enumerable
irb(main):004:1> end
=> NilClass
irb(main):005:0> nil.each {|x| puts x}
=> nil
irb(main):006:0>

?

Kind regards

	robert