From: Robert Klemme <bob.news@...>
Date: 2003-08-12T20:43:33+09:00
Subject: Re: using case with classes


"Ryan Pavlik" <rpav@users.sourceforge.net> schrieb im Newsbeitrag
news:20030811190930.5e03fb72.rpav@users.sf.net...
> On Tue, 12 Aug 2003 10:25:04 +0900
> Michael Garriss <mgarriss@earthlink.net> wrote:
>
> > Ok, this did not work like I expected (because I know too little about
> > Ruby):
> >
> > def test( obj )
> >     case obj.class
> >        when Array then puts "Array"
> >        when Hash  then puts "Hash"
> >        when Class then puts "Class"
> >        else puts "ugh"
> >     end
> > end
>
> try this:
>
>     def test( obj )
>         case obj
>            when Array then puts "Array"
>            when Hash  then puts "Hash"
>            when Class then puts "Class"
>            else puts "ugh"
>         end
>     end
>
> Unfortunately the behavior above is still annoying; in this case you
> have an object to work with, but I've run into a number of cases
> where I have only a class, and I just have to use a big "if" block.

No.

class TypeCheck
  def initialize(cl)
    @cl = cl
  end

  def ===(o)
    @cl == o
  end
end

case Array
  when TypeCheck.new(Array)
    puts "Array"
  when TypeCheck.new(Hash)
    puts "Hash"
  else
    puts "buh!"
end

# even better, because it creates less instances:

def TypeCheck(cl)
  (@@checks ||= Hash.new {|h,k| h[k] = TypeCheck.new(k)} )[cl]
end

case Array
  when TypeCheck(Array)
    puts "Array"
  when TypeCheck(Hash)
    puts "Hash"
  else
    puts "buh!"
end


see also ruby talk 76641

    robert