cannot get attr_accessor to work

[Tom Cloyd]

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
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 Cloyd, MS MA, LMHC - Private practice Psychotherapist
Bellingham, Washington, U.S.A: (360) 920-1226
<< (e-mail address removed) >> (email)
<< TomCloyd.com >> (website)
<< sleightmind.wordpress.com >> (mental health weblog)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

 

[David A. Black]

Hi --

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

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 Collins]

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 -

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 Cloyd]

Hi --



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,

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 Cloyd, MS MA, LMHC - Private practice Psychotherapist
Bellingham, Washington, U.S.A: (360) 920-1226
<< (e-mail address removed) >> (email)
<< TomCloyd.com >> (website)
<< sleightmind.wordpress.com >> (mental health weblog)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

 

[Tom Cloyd]

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 Cloyd, MS MA, LMHC - Private practice Psychotherapist
Bellingham, Washington, U.S.A: (360) 920-1226
<< (e-mail address removed) >> (email)
<< TomCloyd.com >> (website)
<< sleightmind.wordpress.com >> (mental health weblog)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

 

[Justin Collins]

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.

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]

Hi --

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.

The code I saw was:

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 Cloyd]

Hi --



The code I saw was:


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

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 Cloyd, MS MA, LMHC - Private practice Psychotherapist
Bellingham, Washington, U.S.A: (360) 920-1226
<< (e-mail address removed) >> (email)
<< TomCloyd.com >> (website)
<< sleightmind.wordpress.com >> (mental health weblog)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

 

[David A. Black]

Hi --

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 Cloyd]

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

Got it! Makes total sense (in retrospect).

Tks,

t.

--

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Tom Cloyd, MS MA, LMHC - Private practice Psychotherapist
Bellingham, Washington, U.S.A: (360) 920-1226
<< (e-mail address removed) >> (email)
<< TomCloyd.com >> (website)
<< sleightmind.wordpress.com >> (mental health weblog)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~