From: Robert Klemme <bob.news@...>
Date: 2004-02-01T23:04:51+09:00
Subject: Re: Save the flip/flop op!


"Gavin Sinclair" <gsinclair@soyabean.com.au> schrieb im Newsbeitrag
news:1221728269450.20040201235547@soyabean.com.au...
> On Sunday, February 1, 2004, 11:29:50 PM, Robert wrote:
>
> >> Comments, Phil? Nathaniel? Others?
>
> > I wouldn't put it into File or IO since this is too specialized
> > functionality.  It deserves a class of it's own:
>
> > class FlipFlop
> >   def initialize(on, off)
> >     @on, @off = on, off
> >     @state = false
> >   end
> >
> >   def ===(o)
> >     if @state
> >       @state = false if @off === o
> >     else
> >       @state = true if @on === o
> >     end
> >
> >     @state
> >   end
> > end
>
>
> Nice implementation.

Thanks!

>  The usage is still more verbose than the FF
> operator, though.

Yeah, but it avoids the speciality of treating ".." and "..." differently
when they appear in an if clause.

>  Perhaps some method to process an enumerable
> object?
>
> # Untested
> class FlipFlop
>   def process(enum)
>     enum.each do |o|
>       yield(o) if self === o
>     end
>   end
> end
>
>
> File.open(path) do |io|
>   FlipFlop.new(/BEGIN/, /END/).process(io) do |line|
>     puts line
>   end
> end
>
> Is that any good?

It looks good.  The only thing that bothers me a bit is that the iteration
is kind of "hidden".  In Ruby we typically do enum.each{|elem| do sth. with
elem}.  It's just a feeling, I can't exactly point to why this might be bad.
The only thing that comes to my mind is that you make the whole block
dependend on the FF's state while you might want to do something else with
the line even if the FF doesn't match.  E.g. you could be wanting to do:

io.each_line do |line|
  line.chomp!

  case line
  when ff1
    # do stuff
  when ff2
    # do other stuff
    if ff3 === line
      # nested
    end
  end
end

Dunno whether that is realistic.

Regards

    robert