From: Robert Klemme <bob.news@...>
Date: 2005-07-13T22:20:51+09:00
Subject: Re: correct use of join?

Joseph Paish wrote:
> when i run a (large) script i am writing, this is the output i get on
> the screen (there are actually several hundred lines of output).
> note the "nil" on the first line.
>
> nil
> ["10/12/2001", "bought", "10000", "abc", "0.100", 0.2345, "17.43"]
> ["01/02/2005", "sold", "100", "widget2", "0.143", 0.4567, "22.45"]
>
> assuming that each line of the output is called single_record, when i
> type single_record.class, i find out that it is an Array.  so far, so
> good.
>
> when i include the line
>
> puts single_record.join(" ")
>
> in the script in order to print single_record out as a
> space-separated string, i get the following message :
>
> my_command_prompt$ ruby ~/ruby_dir/program_name.rb
> nil
> /my_command_prompt/ruby_dir/program_name.rb:377: undefined method
> `join' for nil:NilClass (NoMethodError)
>         from /my_command_prompt/ruby_dir/program_name.rb:239:in `each'
>         from /my_command_prompt/ruby_dir/program_name.rb:239
>
> when i use irb to do the example on the web page
> http://pine.fm/LearnToProgram/?Chapter=07, everything works perfectly.
>
> if single_record is in fact an array (and single_record.class tells
> me it is), what am i doing wrong?  I have a feeling it has to do with
> the appearance of the word "nil" in the first line of output.

Obviously the first time you access single_record it's nil.  And nil
doesn't join.  You can do several things:

puts single_record && single_record.join(" ")
single_record and puts single_record.join(" ")
puts single_record.join(" ") if single_record
puts single_record.to_a.join(" ")

and probably a lot more.  But maybe it's just a bug that lead to the nil
and it normally cannot happen.

Kind regards

    robert