Forum: Ruby cannot get attr_accessor to work

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Tom C. (Guest)
on 2009-01-21 04:13
(Received via mailing list)
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 -

> > 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

--

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Tom C., MS MA, LMHC - Private practice Psychotherapist
Bellingham, Washington, U.S.A: (360) 920-1226
<< removed_email_address@domain.invalid >> (email)
<< TomCloyd.com >> (website)
<< sleightmind.wordpress.com >> (mental health weblog)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
David A. Black (Guest)
on 2009-01-21 04:22
(Received via mailing list)
Hi --

On Wed, 21 Jan 2009, Tom C. wrote:

> # Set up logging
> run_log = Manage_log.new( 'logfile.txt' ).open
> log = run_log.log
> logging_now = run_log.lgg    # @logging_now = false

I haven't read the rest of your code but I'll bet the problem is right
there. Ruby is interpreting log and logging_now as local variables. If
you want to call the methods of those names, you have to do:

   self.log = run_log.log
   self.logging_now = run_log.lgg

Basically, given any expression that looks like this:

    var = value

the parser interprets var as a local variable name. So you have to add
the explicit receiver to achieve the method call.


David

--
David A. Black / Ruby Power and Light, LLC
Ruby/Rails consulting & training: http://www.rubypal.com
Coming in 2009: The Well-Grounded Rubyist (http://manning.com/black2)

http://www.wishsight.com => Independent, social wishlist management!
Justin C. (Guest)
on 2009-01-21 04:24
(Received via mailing list)
Tom C. wrote:
>  # Set up logging
>  # * _op_ - Requested operation: _open_ or _close
>
> require lib }
>> setnet-x.rb:40
>> 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
Tom C. (Guest)
on 2009-01-21 04:29
(Received via mailing list)
David A. Black wrote:
>>
> you want to call the methods of those names, you have to do:
>
>
> David
>
David,

Thank for your reply, but I'm puzzled by it. Doesn't the code in my
previous post make it clear that I'm dealing with instance variables?
The class instance initiates them, e.g., @log, and I'm trying to get
that with the run_log.log call. This is NOT an attempt to call a method.
I very carefully copied (I thought) the pattern I saw in several
authoritative sources, but it doesn't work for me, which is nuts.

I hope this makes sense.

t.

--

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Tom C., MS MA, LMHC - Private practice Psychotherapist
Bellingham, Washington, U.S.A: (360) 920-1226
<< removed_email_address@domain.invalid >> (email)
<< TomCloyd.com >> (website)
<< sleightmind.wordpress.com >> (mental health weblog)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Tom C. (Guest)
on 2009-01-21 04:39
(Received via mailing list)
Justin C. wrote:
>> def main
>>  #
>>    @lgg = true
>> %w(rubygems ruby-debug readline strscan logger fileutils).each{ |lib|
>>> $ ruby setnet-x.rb
>>> setnet-x.rb:5
>
>
> 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
>
>
Well, nuts. That's crystal clear. Man, it's tough being a Ruby amateur,
when it 's not great fun, which it hasn't been for a couple of hours.

Thanks Justin. Much appreciated.

t.

--

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Tom C., MS MA, LMHC - Private practice Psychotherapist
Bellingham, Washington, U.S.A: (360) 920-1226
<< removed_email_address@domain.invalid >> (email)
<< TomCloyd.com >> (website)
<< sleightmind.wordpress.com >> (mental health weblog)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Justin C. (Guest)
on 2009-01-21 04:44
(Received via mailing list)
Tom C. wrote:
> Justin C. wrote:
>> Tom C. 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 -
>>>
>>>
<snip>
>>
> of hours.
>
> Thanks Justin. Much appreciated.
>
> t.


Just remember that whenever you see

NoMethodError Exception: undefined method `..." for nil:NilClass

look at what variable you are calling the method on. Then figure out why
it is nil.

-Justin
David A. Black (Guest)
on 2009-01-21 04:50
(Received via mailing list)
Hi --

On Wed, 21 Jan 2009, Tom C. wrote:

>>> Here's a stripped down version of the code -
>> there. Ruby is interpreting log and logging_now as local variables. If
>> the explicit receiver to achieve the method call.
> copied (I thought) the pattern I saw in several authoritative sources, but it
> doesn't work for me, which is nuts.
>
> I hope this makes sense.

The code I saw was:

>>> run_log = Manage_log.new( 'logfile.txt' ).open
>>> log = run_log.log
>>> logging_now = run_log.lgg    # @logging_now = false

which are local variable assignments, and you'd mentioned
attr_accessor, so I assumed you had attr_accessor somewhere in a part
of the code you hadn't posted. It's a common error to do:

   class C
     attr_accessor :name
     def initialize(name)
       name = name        # should be @name or self.name
     end
   end

so I surmised that that was what was going on. Oh well -- can't hurt
to see that particular potential problem anyway :-)

I'm still not sure where attr_accessor fits in.


David

--
David A. Black / Ruby Power and Light, LLC
Ruby/Rails consulting & training: http://www.rubypal.com
Coming in 2009: The Well-Grounded Rubyist (http://manning.com/black2)

http://www.wishsight.com => Independent, social wishlist management!
Tom C. (Guest)
on 2009-01-21 05:03
(Received via mailing list)
David A. Black wrote:
>>>> the nut. This SHOULD work, but I'm obviously screwing up. Just
>>>> log = run_log.log
>>>
>> Thank for your reply, but I'm puzzled by it. Doesn't the code in my
>
>     def initialize(name)
> David
>
Sorry you got a partial copy of the code I sent. It rather sounded like
that was what happened. I DO appreciate that you responded so quickly.
You've certainly been very helpful to me on a number of occasions. (And
I require that help, at times, if I'm get anything much accomplished in
Ruby, in the time I have!).

Thanks.

Tom

--

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Tom C., MS MA, LMHC - Private practice Psychotherapist
Bellingham, Washington, U.S.A: (360) 920-1226
<< removed_email_address@domain.invalid >> (email)
<< TomCloyd.com >> (website)
<< sleightmind.wordpress.com >> (mental health weblog)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
David A. Black (Guest)
on 2009-01-21 05:11
(Received via mailing list)
Hi --

On Wed, 21 Jan 2009, Tom C. wrote:

>>>>> I've been staring at this for a couple of hours, and I cannot crack the
>>>>> run_log = Manage_log.new( 'logfile.txt' ).open
>>>> Basically, given any expression that looks like this:
>>>
>>
>>     def initialize(name)
>> David
>>
> Sorry you got a partial copy of the code I sent. It rather sounded like that
> was what happened.

I think I got it all (the bit I quoted was just a few lines of it),
but I surmised too quickly what your problem was. I'm STILL not sure
where attr_accessor fits in :-) (You're not calling it anywhere, are
you?) But it sounds like you got the problem resolved.

> I DO appreciate that you responded so quickly.  You've certainly
> been very helpful to me on a number of occasions. (And I require
> that help, at times, if I'm get anything much accomplished in Ruby,
> in the time I have!).

Glad to be of help!


David

--
David A. Black / Ruby Power and Light, LLC
Ruby/Rails consulting & training: http://www.rubypal.com
Coming in 2009: The Well-Grounded Rubyist (http://manning.com/black2)

http://www.wishsight.com => Independent, social wishlist management!
Tom C. (Guest)
on 2009-01-22 08:39
(Received via mailing list)
Justin C. wrote:
>>>>
>>>
>> amateur, when it 's not great fun, which it hasn't been for a couple
>
> look at what variable you are calling the method on. Then figure out
> why it is nil.
>
> -Justin
>
>
Got it! Makes total sense (in retrospect).

Tks,

t.

--

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Tom C., MS MA, LMHC - Private practice Psychotherapist
Bellingham, Washington, U.S.A: (360) 920-1226
<< removed_email_address@domain.invalid >> (email)
<< TomCloyd.com >> (website)
<< sleightmind.wordpress.com >> (mental health weblog)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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