From: Robert Klemme <bob.news@...>
Date: 2004-02-01T21:29:50+09:00
Subject: Re: Save the flip/flop op!


"Hal Fulton" <hal9000@hypermetrics.com> schrieb im Newsbeitrag
news:401C0A45.3000504@hypermetrics.com...
> Phil Tomson wrote:
> >>That's why I personally would like to see it gone, and good riddance.
> >>You, of course, are welcome to root for a pardon, but I just wanted to
> >>make sure the other side of the aisle was represented :-)
> >>
> > And just what would you replace that functionality with?
>
> Phil,
>
> I'm with Nathaniel. Save the functionality but please KILL the
> syntax. Only a perler could love it. (No offense meant.)
>
> I haven't thought this through yet. But let's do it with a
> method call.
>
>    #untested
>    f.set_context(/BEGIN/,/END/)
>    f.each_line do |l|
>      if f.in_context
>        # do something with l...
>      else
>        # whatever
>      end
>    end
>
>
> 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

io=<<TEXT
foo
BEGIN
bar
BEGIN
baz
END
bar
TEXT

ff = FlipFlop.new /BEGIN/, /END/

io.each_line do |line|
  line.chomp!
  puts "#{ff === line}: #{line}"
end

Yields

false: foo
true: BEGIN
true: bar
true: BEGIN
true: baz
false: END
false: bar

If you want to include the last line you can do:

class FlipFlop2
  def initialize(on, off)
    @on, @off = on, off
    @state = false
  end

  def ===(o)
    old = @state

    if @state
      @state = false if @off === o
    else
      old = @state = true if @on === o
    end

    old
  end
end

Yields:

false: foo
true: BEGIN
true: bar
true: BEGIN
true: baz
true: END
false: bar

Regards

    robert