Asp Forum - Nested Modules/Classes

Ken Mitchell

4/2/2007 9:03:00 PM

I have what I feel should be a simple issue. Look at the following:

############################
# Test of nested modules/classes
############################
class Global
module TestMod
TEST = "test1"
def print_test
puts "test2"
end
end#module TestMod

include TestMod
puts TEST
print_test

end#class Global
##############################

->test1
->test.rb:22: undefined local variable or method 'print_test' for
Global:Class

Whether "Global" is a Class or a Method the same happens. However, if I
comment out "Global" completely, out put is as expected:

->test1
->test2

Thanks in advance.

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7 Answers

Ryan Leavengood

4/2/2007 9:30:00 PM

On 4/2/07, Ken Mitchell <kmitchell@farmerswireless.com> wrote:
> I have what I feel should be a simple issue. Look at the following:
>
> ############################
> # Test of nested modules/classes
> ############################
> class Global
> module TestMod
> TEST = "test1"
> def print_test
> puts "test2"
> end
> end#module TestMod
>
> include TestMod

You only include the module, therefore any methods defined in it will
only be instance methods. By trying to call print_test from inside the
class definition you are calling it as a class method. If you want
print_test to also be a class method you must extend TestMod as well
as including it.

Basically include adds the module's methods as instance methods and
extend adds them as class methods.

Ryan

Brian Candler

4/2/2007 9:30:00 PM

On Tue, Apr 03, 2007 at 06:02:41AM +0900, Ken Mitchell wrote:
> I have what I feel should be a simple issue. Look at the following:
>
> ############################
> # Test of nested modules/classes
> ############################
> class Global
> module TestMod
> TEST = "test1"
> def print_test
> puts "test2"
> end
> end#module TestMod
>
> include TestMod
> puts TEST
> print_test
>
> end#class Global
> ##############################
>
> ->test1
> ->test.rb:22: undefined local variable or method 'print_test' for
> Global:Class
>
> Whether "Global" is a Class or a Method the same happens. However, if I
> comment out "Global" completely, out put is as expected:
>
> ->test1
> ->test2

If you 'include' a module in a class, its methods are added as instance
methods for objects of that class. Try:

a = Global.new
a.print_test

Stefano Crocco

4/2/2007 9:32:00 PM

Alle lunedì 2 aprile 2007, Ken Mitchell ha scritto:
> I have what I feel should be a simple issue. Look at the following:
>
> ############################
> # Test of nested modules/classes
> ############################
> class Global
> module TestMod
> TEST = "test1"
> def print_test
> puts "test2"
> end
> end#module TestMod
>
> include TestMod
> puts TEST
> print_test
>
> end#class Global
> ##############################
>
> ->test1
> ->test.rb:22: undefined local variable or method 'print_test' for
> Global:Class
>
> Whether "Global" is a Class or a Method the same happens. However, if I
> comment out "Global" completely, out put is as expected:
>
> ->test1
> ->test2
>
> Thanks in advance.

When you include TestMod in the class Global, the instance methods of TestMod
become instance methods of Global, that is, they become methods of the
instances of Global, not of Global itself. So, you can do:

Global.new.print_test
=> "test2"

The same happens if Global were a module.

If you want to add the instance methods of TestMod to Global itself, instead,
you can do the following:

class Global
module TestMod
...
end #End of TestMod
extend TestMod
end

While Module#include adds the instance methods of the module as instance
methods of the class (or module) where it's called, extend adds the instance
methods of the module to its receiver (self, in this case).

I hope this helps

Stefano

Ken Mitchell

4/2/2007 9:43:00 PM

Brian Candler wrote:
> On Tue, Apr 03, 2007 at 06:02:41AM +0900, Ken Mitchell wrote:
>> end
>> ->test.rb:22: undefined local variable or method 'print_test' for
>> Global:Class
>>
>> Whether "Global" is a Class or a Method the same happens. However, if I
>> comment out "Global" completely, out put is as expected:
>>
>> ->test1
>> ->test2
>
> If you 'include' a module in a class, its methods are added as instance
> methods for objects of that class. Try:
>
> a = Global.new
> a.print_test

Thank you two! See, I knew it would be simple and now it even makes
sense.

So in the context of the above, my application will be performing a wide
range of work and will need to be quite modular (ok I'm lazy). As far
as preference and "best practice", how would I best layout the
namespace. For instance:

#/lib/testapp.rb
#/lib/testapp/config.rb
#/lib/testapp/logger.rb

maybe this....

module Testapp
module config
end

class logger
end
end

Looking through included source, I see this done so many different ways.
What is the best. Thanks so much

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Ken Mitchell

4/2/2007 9:45:00 PM

Sorry for the Double Post, thank you Stefano I missed you.

Where is the mailing list located. I cannot find it, only these forums.
It seems that some of you guys are using maillist functionality

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Ilan Berci

4/2/2007 9:50:00 PM

Ken Mitchell wrote:
> I have what I feel should be a simple issue. Look at the following:
>
> ############################
> # Test of nested modules/classes
> ############################
> class Global
> module TestMod
> TEST = "test1"
> def print_test
> puts "test2"
> end
> end#module TestMod
>
> include TestMod
> puts TEST
> print_test
>
> end#class Global
> ##############################
>
> ->test1
> ->test.rb:22: undefined local variable or method 'print_test' for
> Global:Class
>
> Whether "Global" is a Class or a Method the same happens. However, if I
> comment out "Global" completely, out put is as expected:
>
> ->test1
> ->test2
>
> Thanks in advance.

irb(main):004:0> class Global
irb(main):005:1> module TestMod
irb(main):006:2> TEST = "test1"
irb(main):007:2> def print_test
irb(main):008:3> puts "test2"
irb(main):009:3> end
irb(main):010:2> end
irb(main):011:1> extend TestMod
irb(main):012:1> end
=> Global
irb(main):013:0> Global.print_test
test2
=> nil

ilan

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Ryan Leavengood

4/2/2007 9:55:00 PM

On 4/2/07, Ken Mitchell <kmitchell@farmerswireless.com> wrote:
>
> Where is the mailing list located. I cannot find it, only these forums.
> It seems that some of you guys are using maillist functionality

Hi Ken,

The Ruby Forum is useful for the occasional post. It forwards your
messages to the ruby-talk mailing list. If you would like to subscribe
to ruby-talk go here:

http://www.ruby-lang.org/en/community/mail...

You can learn a lot about Ruby by reading the messages posted here.

Regarding your question about how to structure your Ruby code, here
are my suggestions:

- create a Module as the namespace for all the classes in your
application or library.
- create the classes you need inside that module.
- if you find classes with common functionality, see if you can break
that out into modules which are included in those classes.
- I recommend using the Test::Unit library to unit test your classes.
An example of this is in my recent Ruby Quiz submission:

http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-t...

Good luck with Ruby and welcome to our community. As you can see we
are a pretty friendly and helpful bunch :)

Regards,
Ryan

comp.lang.ruby

Nested Modules/Classes

Ken Mitchell

Ryan Leavengood

Brian Candler

Stefano Crocco

Ken Mitchell

Ken Mitchell

Ilan Berci

Ryan Leavengood

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