From: Jeff Mitchell <quixoticsycophant@...>
Date: 2004-07-07T18:38:18+09:00
Subject: Re: Class#=== has interesting results

--- Charles Comstock <cc1@cec.wustl.edu> wrote:
> > 
> > whatisit = case obj
> > 	   when Array
> > 	      "it's an array!"
> > 	   when Hash
> > 	      "it's a hash!"
> > 	   when Septuagenarian
> > 	      "it's a septuagenarian!"
> > 	   end
> > 
> > $ ri Module#===
> > ------------------------------------------------------------- Module#===
> >      mod === obj    => true or false
> > ------------------------------------------------------------------------
> >      Case Equality---Returns +true+ if _anObject_ is an instance of
> >      _mod_ or one of _mod_'s descendents. Of limited use for modules,
> >      but can be used in +case+ statements to classify objects by class.
> > 
> 
> Right I was trying to use it in an example almost exactly like that 
> except that obj was a name of a commandclass.
> 
> Ie:
>    def parse(str)
>      input = str.chomp.split
>      comm = CommandFactory[input[0]]
> 
>      case comm
>      when StartCommand
>        comm.new(input[1],input[2..-1])
>        @mobile = input[1]
>      when HelpCommand
>      else
>        comm.new(@mobile,input[1..-1])
>      end
>    end
> 
> The idea was for a command factory to return the name of the command, 
> and instantiate that command with the rest of the string as parameters, 
> except for a few special case examples which would be checked against in 
> a case statement.  Since StartCommand === StartCommand returns false 
> this doesn't work.  Why you would want == to return true and === to 
> return false in this case is beyond me. I knew about the example you 
> gave above, that was what I was trying to emulate except at a step before.

I'm not sure what you mean.  StartCommand is not and instance of
StartCommand or one of its decendants, therefore 

StartCommand === StartCommand

returns false.  Did you want the case statement behave differently
different when given a class?

Does this help:

      case comm.to_s.intern
      when :StartCommand
        comm.new(input[1],input[2..-1])
        @mobile = input[1]
      when :HelpCommand
      else
        comm.new(@mobile,input[1..-1])
      end



	
		
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