From: Robert Klemme <bob.news@...>
Date: 2003-07-22T17:10:46+09:00
Subject: Re: Case Checks


"Martin DeMello" <martindemello@yahoo.com> schrieb im Newsbeitrag
news:t%4Ta.29045$Ma.6022851@news1.telusplanet.net...
> Robert Klemme <bob.news@gmx.net> wrote:
> > When I couldn't sleep this morning, this came across my head:
> >
> > class Check
> >  def initialize(sym, args)
> >    @args=args
> >    instance_eval "def ===(obj); obj.#{sym}(*@args); end"
> >  end
> >
> >  class <<self
> >    def create(sym=nil, *args, &bl)
> >      if bl
> >        def bl.===(obj); call(obj); end
> >        bl
> >      elsif sym
> >        new sym, args
> >      else
> >        raise "Need either block or symbol with arguments"
> >      end
> >    end
> >
> >    private :new
> >  end
> > end
>
>
> Very nice! Here's an extension (untested):

> def check(*args, &block)
>   checks = args
>   checks << Check.create(block) if block
>   class << checks
>     def ===(obj)
>       all? {|i| i === obj}
>     end
>   end
>   checks
> end

The create method is not called correctly.  But I like the shorter
creation, i.e.,

check {|x| x == "bar"}

Corrected:

def check(*args, &block)
  checks = args
  checks << Check.create(&block) if block

  class <<checks
    def ===(obj)
      all? {|i| i === obj}
    end
  end

  checks
end

Of course, invoking check outside the case is more efficient for cases
where case is executed often.

> allowing
>
> case i
>   when check(Positive, Div5) {|x| x > 100}

    robert