From: Justin Collins <justincollins@...>
Date: 2009-01-21T11:21:06+09:00
Subject: Re: cannot get attr_accessor to work

Tom Cloyd wrote:
> I've been staring at this for a couple of hours, and I cannot crack 
> the nut. This SHOULD work, but I'm obviously screwing up. Just cannot 
> see where. I'm carefully following several examples, but...I cannot 
> get access to my instance variables.
>
> Here's a stripped down version of the code -
>
> # SetNet.rb
>
> def main
>  # Set up logging
>  run_log = Manage_log.new( 'logfile.txt' ).open
>  log = run_log.log
>  logging_now = run_log.lgg    # @logging_now = false
>    # @log, @logging_now = manage_log( 'open' )
> end
>
> # Creates program log file, setting default logging level of INFO. 
> Current logging is appended to existing log content. Closes log when 
> requested by user.
>  #
>  # * _op_ - Requested operation: _open_ or _close
>  #
> class Manage_log  attr_accessor :log, :lgg
>  def initialize( logFileName )
>    @logFileName = logFileName
>  end
>  def open    #create log file
>    log_main = File.open( @logFileName, File::WRONLY | File::APPEND )
>    @log = Logger.new( log_main )
>    @log.datetime_format = "%Y-%m-%d %H:%M:%S"
>    @lgg = true
>
>    # set logging level
>    @log.level = Logger::INFO # I.e., only INFO level and above will be 
> logged
>    @log.info( '===== START logging' ) # just a program place indicator
>    puts '> logging started, at INFO level'
>  end
>
> end
>
> %w(rubygems ruby-debug readline strscan logger fileutils).each{ |lib| 
> require lib }
> Debugger.start
> debugger # call to ruby-debug
>
> main
>
> ====
>
> Demonstration of the lack of access -
>
>> $ ruby setnet-x.rb
>> setnet-x.rb:40
>> main
>> (rdb:1) b 4
>> Breakpoint 1 file setnet-x.rb, line 4
>> (rdb:1) c
>> Breakpoint 1 at setnet-x.rb:4
>> setnet-x.rb:4
>> run_log = Manage_log.new( 'logfile.txt' ).open
>> (rdb:1) n
>> > logging started, at INFO level
>> setnet-x.rb:5
>> log = run_log.log
>> (rdb:1) p run_log.log
>> NoMethodError Exception: undefined method `log' for nil:NilClass
>> (rdb:1)
> I would truly appreciate someone's pointing out the problem here.
>
> Thanks!
>
> Tom
>


Take a look at ManageLog#open. The last expression is a call to puts, 
which returns nil. You are setting the variable "run_log" to the result 
of the call to open in the debugger, but that result is nil. Then you 
try to call "log" on nil, thus the error.

-Justin