From: Jim Freeze <jfreeze@...>
Date: 2002-08-14T03:16:26+09:00
Subject: Re: FileTest module confusion

On Wed, Aug 14, 2002 at 02:50:28AM +0900, James Toomey wrote:
> I'm just learning Ruby, so please forgive any naivete revealed here.
> In the following code,
> #---------------------------------------
> class DummyClass
>   include FileTest
> end
> DummyInstance = DummyClass.new
> #This works
> puts FileTest.exists?("c:\\autoexec.bat")
> #This doesn't work
> puts DummyInstance.exists?("c:\\autoexec.bat")
Try
  puts DummyInstance::FileTest.exists?("c:\\autoexec.bat")

I believe that the exists? (and family) are module methods.

> #---------------------------------------
> it seems like the FileTest module acts more like a class than a
> module. From what I've read, modules can be used as "mixins" to
> enhance existing classes but cannot be instantiated on their own.
> However, the opposite seems to be occurring.
> If I substitute the FileTest module for my own module, the expected
> behavior occurs:
> #---------------------------------------
> module SampleModule
>  def displayMessage
>   return "Hello World!"
>  end
> end
> class DummyClass2
>   include SampleModule
> end
> DummyInstance2 = DummyClass2.new
> #This works
> puts DummyInstance2.displayMessage
> #This doesn't work
> puts SampleModule.displayMessage

You can replicate FileTest behaviour with the following:
  module SampleModule
  def self.displayMessage
   return "Hello World!"
  end
  end
  class DummyClass2
    include SampleModule
  end
  DummyClass2.SampleModule.displayMessage
irb(main):010:0> DummyClass2::SampleModule.displayMessage
"Hello World!"
irb(main):011:0> DummyClass2.displayMessage
NameError: undefined method `displayMessage' for DummyClass2:Class
        from (irb):11


Hope that helps.

> #---------------------------------------
> Am I using the FileTest module incorrectly? And if FileTest can be
> used as a standalone object (instead of being mixed in), why isn't it
> a class instead of a module? I know there's the File::Stat object, but
> it seems to operate a bit differently than FileTest.

-- 
Jim Freeze
If only I had something clever to say for my comment...
~