From: Gavin Sinclair <gsinclair@...>
Date: 2002-10-24T22:00:39+09:00
Subject: Re: Read "current line" from a file?

From: <dblack@candle.superlink.net>


> Hi --
>
> On Thu, 24 Oct 2002, Gavin Sinclair wrote:
>
> > All,
> >
> > Given an IO object, you can get the "next" line with #gets, right?
> >
> > Given an IO object, you can get the "current" line with #X, right?  Please?
> >
> > I know it's not a common operation, but I would like tobe able to do it.
>
> Do you mean a kind of one-line lookahead?  I had occasion to do that
> somewhere recently, and did:
>
>   class File
>     def ungets(str)
>       seek(pos - str.size,0)
>     end
>
>     # One-line lookahead.
>     def next_line
>       line = gets
>       ungets(line) if line
>       line
>     end
>   end
>
>
> David

Hmmm... I might give that a go.  This is the sort of thing I'm trying to do.
I've got the following code:

      file.reverse_each do |line|
        if line =~ /Published/
          timestamp = collect_timestamp(line)
          line = file.gets && file.gets
          unless line.nil?
            backend_id = collect_backend_id(line)
            ...
          end
        end
      end

And I'd like to refactor it to:

      file.reverse_each do |line|
        if line =~ /Published/
          timestamp, backend_id = collect_data(file)
        end
      end

      def collect_data(file)
        timestamp = collect_timestamp(file.current_line)
        line = file.gets && file.gets
        unless line.nil?
          backend_id = collect_backend_id(line)
          ...
        end
      end


File#reverse_each is a nifty method I wrote to process a file in reverse line
order.  I was (obviously) hoping that IO/File would have a buffer of the
current line that it can share with me!  If I have to hack it, then I don't
really achieve anything pretty.

Thanks,
Gavin