From: Troy Denkinger <tdenkinger@...>
Date: 2006-03-04T03:15:59+09:00
Subject: Re: Dynamic Object Instantiation

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Thanks for the followup.  I also figured out how to search and found this:

http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/13414?help-en

Which also helps.

Thanks.

On 3/1/06, Joel VanderWerf <vjoel@path.berkeley.edu> wrote:
>
> Troy Denkinger wrote:
> > I'm sure this question has been asked and answered in the past, but
> googling
> > and searching the list archives isn't getting me much.  It's probably a
> case
> > of me not searching correctly.  So, if someone has a pointer on that
> front,
> > let me know.
> >
> > Basically, I want a class to dynamically load and instantiate objects.
> > Here's the code that is supposed to do that:
> >
> > ComponentGatherer.rb
> > ---------------------------------
> >
> > class ComponentGatherer
> >
> >   def initialize()
> >     @@components =3D []
> >     Dir.foreach( File.dirname( __FILE__ ) ){|x|
> >       next unless x =3D~ /component.rb$/i
> >       x.gsub!( ".rb", "" )
> >       require "#{x}"
> >       @@components.push( x )
> >     }
> >   end
> >
> >   def components
> >     @@components.each{ |x|
> >         test =3D x.new()
> >        # Blah, blah, blah
> >     }
> >   end
> > end
> >
> >
> > Locating and requring the files seems to be working fine, it's when the
> > component() call is made that I'm a bit lost.  I have to
> > *Component.rbfiles, they look like this:
> >
> > MyOtherComponent.rb
> > --------------------------------
> > class MyOtherTestComponent
> >
> >   attr :test
> >
> >   def initialize()
> >     self.test =3D 2
> >   end
> > end
> >
> > The error I get from the components() method is:
> >
> >   undefined method `new' for "MyOtherTestComponent":String
> (NoMethodError)
> >
> > I understand what the error is saying, but I'm not sure how to call
> new() on
> > "x" above such that it returns an object of the requested class.  Any
> help
> > is appreciated.
> >
> > Regards,
> >
> > Troy Denkinger
> >
>
> If there is a way to map from the file name to the class name (in this
> example, it would map "MyOtherComponent.rb" to "MyOtherTestComponent"),
> then you can do this first, and then use const_get to get the class:
>
>   x =3D "MyOtherComponent.rb"
>   x.gsub(/.rb$/, "")
>   x.gsub(/Component/, "TestComponent")
>   cl =3D Kernel.const_get x
>   obj =3D cl.new
>
> But it's sometimes difficult to enforce this filename/classname
> consistency.
>
> I prefer something like this:
>
> http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/181735
>
> It still uses const_get, but it wraps the component inside a module, so
> that the global namespace doesn't get polluted, and you can query for
> the class that was defined in a file without mucking around with the
> file name.
>
> HTH.
>
> --
>       vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407
>
>

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