# Newbie question about scope, variables, declarations of vari **URL:** \ **Category:** Ruby\ **Created:** [March 8, 2006, 10:03am UTC](https://www.ruby-forum.com/t/newbie-question-about-scope-variables-declarations-of-vari/78328 "2006-03-08T10:03:47Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![Talha\_O](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/c2a13f/32.png) [@Talha\_O](https://www.ruby-forum.com/u/Talha_O)\ **Post date:** [March 8, 2006, 10:03am UTC](https://www.ruby-forum.com/t/newbie-question-about-scope-variables-declarations-of-vari/78328/1 "2006-03-08T10:03:47Z")
Hello, I am trying to understand the syntax error I receive in a code similar to this. 1 require ‘logger’ 2 3 log = logger.new #some other logger settings are ignored. 4 def func 5 log.debug “a statement” # error is reported here when func is called below 6 # some code 7 end 8 9 #some code continues 10 func When func is called, an error is reported on line-5 saying that undefine local variable log etc. I understand that functions create scopes and log is seen as local variable which is not defined in that scope. As it is qualified with no scope operator, interpreter thinks that it is local but can not find definition of the log before it’s usage but also in the parameter list and I understand that. On the other hand, I can use log without qualifying it with a scope symbol anywhere in the same file if it is not in a function. I know that loops, if statements etc are built into the language and do not create scope. Code blocks inherit the locals. So it is meaningful that I can use it anywhere else. When I qualify log with $ as $log, it becomes global and I no longer receive error. I have tried it qualifying with @ etc. but the received the same error. What I am asking is, what is scope of log?. What kind of variable is it? It is the local or instance variable of what, Object? I know that func is private to the Object. But what about log? How can I access it in a function without making it global? Is there a way to make variables local to a file as perl does with “my”. Is there a strict option that prevents unintended variable creation because of typos. Is there a way force predeclaration of variables? Thanks. ---
**Author:** ![Talha\_O](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/c2a13f/32.png) [@Talha\_O](https://www.ruby-forum.com/u/Talha_O)\ **Post date:** [March 8, 2006, 2:51pm UTC](https://www.ruby-forum.com/t/newbie-question-about-scope-variables-declarations-of-vari/78328/2 "2006-03-08T14:51:14Z")
On Mar 8, 2006, at 3:01 AM, Talha O. wrote: > When I qualify log with $ as > $log, it becomes global and I no longer receive error. I have tried it > qualifying with @ etc. but the received the same error. No, this works too (after you fix your Logger constructor call): require ‘logger’ @log = Logger.new(“test.log”) #some other logger settings are ignored. def func @log.debug “a statement” # error is reported here when func is called below # some code end #some code continues func > What I am asking is, what is scope of log? It’s a local variable, scoped to the file it is defined in. It would not be available inside class, module, or method definitions though, because they are not closures. > What kind of variable is it? Local. > It is the local or instance variable of what, Object? To the file. > But what about log? How can I access it in a function without > making it global? You could pass it as a parameter, or make it an instance variable, as shown above. > Is there a way to make variables local to a file as perl does with > “my”. This is how it functions. > Is there a strict option that prevents unintended variable creation > because > of typos. Is there a way force predeclaration of variables? You must assign to a local before you can use it in Ruby. That’s why you got the error. 😉 James Edward G. II ---
**Author:** ![Talha\_O](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/c2a13f/32.png) [@Talha\_O](https://www.ruby-forum.com/u/Talha_O)\ **Post date:** [March 8, 2006, 3:43pm UTC](https://www.ruby-forum.com/t/newbie-question-about-scope-variables-declarations-of-vari/78328/3 "2006-03-08T15:43:07Z")
Hi – On Wed, 8 Mar 2006, James Edward G. II wrote: > @log = Logger.new(“test.log”) #some other logger settings are ignored. > > def func > @log.debug “a statement” # error is reported here when func is called below That’s a different @log from the one you assigned to, though. David – David A. Black (removed\_email\_address@domain.invalid) Ruby Power and Light, LLC ([http://www.rubypowerandlight.com](http://www.rubypowerandlight.com)) “Ruby for Rails” chapters now available from Manning Early Access Program! [Ruby for Rails](http://www.manning.com/books/black) ---
**Author:** ![Talha\_O](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/c2a13f/32.png) [@Talha\_O](https://www.ruby-forum.com/u/Talha_O)\ **Post date:** [March 8, 2006, 4:38pm UTC](https://www.ruby-forum.com/t/newbie-question-about-scope-variables-declarations-of-vari/78328/4 "2006-03-08T16:38:27Z")
Hi – On Thu, 9 Mar 2006, James Edward G. II wrote: > > > > qualifying with @ etc. but the received the same error. > > p @log.object\_id > 923180 > 923180 Weird. I guess Logger does something bizarre in its constructor. David – David A. Black (removed\_email\_address@domain.invalid) Ruby Power and Light, LLC ([http://www.rubypowerandlight.com](http://www.rubypowerandlight.com)) “Ruby for Rails” chapters now available from Manning Early Access Program! [Ruby for Rails](http://www.manning.com/books/black) ---
**Author:** ![Talha\_O](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/c2a13f/32.png) [@Talha\_O](https://www.ruby-forum.com/u/Talha_O)\ **Post date:** [March 8, 2006, 4:47pm UTC](https://www.ruby-forum.com/t/newbie-question-about-scope-variables-declarations-of-vari/78328/5 "2006-03-08T16:47:33Z")
On Mar 8, 2006, at 9:38 AM, removed\_email\_address@domain.invalid wrote: > Weird. I guess Logger does something bizarre in its constructor. I guess I don’t understand what you are getting at. This is the normal behavior for any object: Neo:~/Desktop$ ls test.rb Neo:~/Desktop$ cat test.rb @obj = Object.new p @obj.object\_id def func p @obj.object\_id end func Neo:~/Desktop$ ruby test.rb 957270 957270 James Edward G. II ---
**Author:** ![Talha\_O](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/c2a13f/32.png) [@Talha\_O](https://www.ruby-forum.com/u/Talha_O)\ **Post date:** [March 8, 2006, 4:07pm UTC](https://www.ruby-forum.com/t/newbie-question-about-scope-variables-declarations-of-vari/78328/6 "2006-03-08T16:07:55Z")
On Mar 8, 2006, at 8:39 AM, removed\_email\_address@domain.invalid wrote: > > > > That’s a different @log from the one you assigned to, though. I’m not sure why you say this, but you’re wrong. 😉 Here’s the proof: Neo:~/Desktop$ ls log.rb Neo:~/Desktop$ cat log.rb require ‘logger’ @log = Logger.new(“test.log”) #some other logger settings are ignored. p @log.object\_id def func @log.debug “a statement” # error is reported here when func is called below p @log.object\_id # some code end #some code continues func Neo:~/Desktop$ ruby log.rb 923180 923180 Neo:~/Desktop$ cat test.log # Logfile created on Wed Mar 08 09:04:50 CST 2006 by logger.rb/1.5.2.7 D, [2006-03-08T09:04:50.196373 #5517] DEBUG – : a statement James Edward G. II ---
**Author:** ![Talha\_O](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/c2a13f/32.png) [@Talha\_O](https://www.ruby-forum.com/u/Talha_O)\ **Post date:** [March 8, 2006, 4:59pm UTC](https://www.ruby-forum.com/t/newbie-question-about-scope-variables-declarations-of-vari/78328/7 "2006-03-08T16:59:48Z")
Hi – On Thu, 9 Mar 2006, James Edward G. II wrote: > @obj = Object.new > p @obj.object\_id > > def func > p @obj.object\_id > end > > func > Neo:~/Desktop$ ruby test.rb > 957270 > 957270 For some reason I had hallucinated that the original example was inside a class definition body, rather than at the top level. Ignore me… David – David A. Black (removed\_email\_address@domain.invalid) Ruby Power and Light, LLC ([http://www.rubypowerandlight.com](http://www.rubypowerandlight.com)) “Ruby for Rails” chapters now available from Manning Early Access Program! [Ruby for Rails](http://www.manning.com/books/black) ---
**Author:** ![Talha\_O](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/c2a13f/32.png) [@Talha\_O](https://www.ruby-forum.com/u/Talha_O)\ **Post date:** [March 8, 2006, 4:59pm UTC](https://www.ruby-forum.com/t/newbie-question-about-scope-variables-declarations-of-vari/78328/8 "2006-03-08T16:59:41Z")
On Mar 8, 2006, at 10:38 AM, removed\_email\_address@domain.invalid wrote: > Weird. I guess Logger does something bizarre in its constructor. At the top level ‘self’ references the same object in the file scope and in the method scope (really private instance methods of the top- level object). Why then is it puzzling that the instance variables are accessible from either place? @a = ‘this is @a’ puts “top: self: #{self.object\_id}” puts “top: @a: #{@a}” def foo puts “foo: self: #{self.object\_id}” puts “foo: @a: #{@a}” end foo put that code in a file and run it: top: self: 1019060 top: @a: this is @a foo: self: 1019060 foo: @a: this is @a Gary W. ---
**Author:** ![Talha\_O](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/c2a13f/32.png) [@Talha\_O](https://www.ruby-forum.com/u/Talha_O)\ **Post date:** [March 8, 2006, 5:12pm UTC](https://www.ruby-forum.com/t/newbie-question-about-scope-variables-declarations-of-vari/78328/9 "2006-03-08T17:12:01Z")
Hi – On Thu, 9 Mar 2006, removed\_email\_address@domain.invalid wrote: > On Mar 8, 2006, at 10:38 AM, removed\_email\_address@domain.invalid wrote: > > > Weird. I guess Logger does something bizarre in its constructor. > > At the top level ‘self’ references the same object in the file scope > and in the method scope (really private instance methods of the top-level > object). Why then is it puzzling that the instance variables are > accessible from either place? See my last message – for some reason I projected a class definition body onto the example when I read it. David – David A. Black (removed\_email\_address@domain.invalid) Ruby Power and Light, LLC ([http://www.rubypowerandlight.com](http://www.rubypowerandlight.com)) “Ruby for Rails” chapters now available from Manning Early Access Program! [Ruby for Rails](http://www.manning.com/books/black)