Cannot get attr_accessor to work


#1

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)

#2

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!


#3

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


#4

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)

#5

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 -

>> > 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


#6

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)

#7

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)

#8

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 :slight_smile: (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!


#9

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)

#10

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 :slight_smile:

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!