Forum: Ruby simple module method call question

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Tom C. (Guest)
on 2009-04-17 16:01
(Received via mailing list)
I'm making no progress on this, and so clearly have missed something
basic.

I have a class which requires a file containing module Utils_db. There
is another module 'required' in the program which instantiates this
class.

I then successfully access in the class two constants - one from each
module.

Utils::MENU
Utils_db::MENU

Now the trouble starts.

Right after accessing the constants, I try to call a method in one of
the modules -

eval("Utils.orph_chk")  <= I will be replacing the string with a
construction using a variable, in the final version

This always fails. I've tried every trick I can think of, but always I
get this:

../lib/setnet/SN.rb:579:in `proc_command': undefined method `orph_chk'
for Utils:Module (NoMethodError)
        from ../lib/setnet/SN.rb:229:in `eval'
        from ../lib/setnet/SN.rb:579:in `proc_command'
        from ../lib/setnet/SN.rb:229:in `user_interface'
        from ../lib/setnet/SN.rb:146:in `manage'
        from ../lib/setnet/SN.rb:68:in `startup'
        from ./setnet:28

Can someone suggest why I'm not able to get to this method?

Here's the relevant Module, in abbreviated form:

module Utils

  MENU = [
  ["orph_chk", "searches nodes and links for references which cannot be
resolved, and reports them"],
  ["tree_count","starting with node 'root', locates descendants of each
node, displaying count at each level"],
  ["showtree","starting with node 'root', locates and displays
descendants of each node"],
  ["tree_orphans","locates links which cannot be traced to the root
node, and displays them"]
  ]

  def orph_chk
    puts 'orph_chk'
  end

end

Any suggestions would be much appreciated. I cannot quite figure out
what to try next.

Thanks,

Tom
James C. (Guest)
on 2009-04-17 16:07
(Received via mailing list)
>       from ./setnet:28
>  ["tree_count","starting with node 'root', locates descendants of each
>
> end



You've defined an instance method, not a module method. The method as
you
define it will appear in classes that use 'include Utils'. To get a
module
method, define it on self:

module Utils
  MENU = [ ... ]

  def self.orph_chk
    # ...
  end
end
Ben L. (Guest)
on 2009-04-17 16:17
(Received via mailing list)
On Fri, Apr 17, 2009 at 1:00 PM, Tom C. <removed_email_address@domain.invalid> 
wrote:

>       from ../lib/setnet/SN.rb:579:in `proc_command'
>
> Tom
>

Hi,

Why are you eval'ing this? This works:

eval("include Utils; Utils.orph_chk")

I would think it has something to do with your binding when you eval.

Ben
Tom C. (Guest)
on 2009-04-17 18:41
(Received via mailing list)
James C. wrote:
>>       from ./setnet:28
>>  ["tree_count","starting with node 'root', locates descendants of each
>>
>   MENU = [ ... ]
>
Well. Live and learn. Very simple solution, but I sure wasn't looking in
THAT corner of the universe.

Thank you very much.

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 2009-04-17 18:41
(Received via mailing list)
Ben L. wrote:
>> Utils:Module (NoMethodError)
>>
>> Thanks,
>>
>> Tom
>>
>>
>
> Hi,
>
> Why are you eval'ing this?
Because the name of one of my two modules isn't known until class
instantiation time. It could literally be anything. That said, I'm not
at all sure my approach is the best. It's just the only one I could
think of. It's also my very first use of eval, and it well may be poorly
chosen.
> This works:
>
> eval("include Utils; Utils.orph_chk")
>
Hmm. I tried that, and got some kind of method error on the "include". I
studied it for a good long while and simply couldn't see the problem.
> I would think it has something to do with your binding when you eval.
>
Yeah, me two. I've never even thought about binding issues before, but I
sure am now!

Thanks for your thoughts.

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)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Suraj K. (Guest)
on 2009-04-18 03:18
James C. wrote:
> You've defined an instance method, not a module method. The method as
> you define it will appear in classes that use 'include Utils'. To get a
> module method, define it on self:
>
> module Utils
>   MENU = [ ... ]
>
>   def self.orph_chk
>     # ...
>   end
> end

Alternatively, you could use module_function() to make the instance
method a class method on the module:

module Utils
  def orph_chk
    # ...
  end

  module_function :orph_chk
end


Now you can either call the method directly (Utils.orph_chk) or mix it
in (include Utils; orph_chk).  So you can have your cake and eat it too!
Tom C. (Guest)
on 2009-04-18 19:47
(Received via mailing list)
Suraj K. wrote:
>>     # ...
>   end
>
>   module_function :orph_chk
> end
>
>
> Now you can either call the method directly (Utils.orph_chk) or mix it
> in (include Utils; orph_chk).  So you can have your cake and eat it too!
>
Hmmm. This is most interesting. Ruby amazes me every day. So much
built-in cleverness. And now this, which I've never seen anywhere. I'll
study up on it. Thanks very much for the heads up,

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)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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