From: Michael Neumann <mneumann@...>
Date: 2004-06-14T17:14:09+09:00
Subject: Re: [RCR]: Replace pack and unpack with OO versions

On Mon, Jun 14, 2004 at 02:48:38PM +0900, Martin DeMello wrote:
> Bill Atkins <dejaspam@batkins.com> wrote:
> > Rather than having code like this:
> > 
> > flags, ignore, length, name = data.unpack "nnna*"
> > 
> > let's try this:
> > 
> > u = Unpacker.new data
> > flags, ignore, length, name = u.word, u.word, u.word, u.string
> > 
> > I think this looks a lot neater and is much more maintainable.  A
> > similar thing could be done with pack.
> 
> Alternatively, something I've been thinking of is to let pack and unpack
> take array arguments, which are 'compiled' into pack/unpack strings.
> 
> e.g.  flags, ignore, length, name = u.unpack [:word, :word, :word,
> :string]
> 
> All the compiler would have to do is translate symbols, and pass numbers
> through unchanged. Or, if you wanted to construct it in terms of pairs
> like [[:string, 3]], just run a flatten first.

It would be nice if Packer/Unpacker would work on IO/File objects. I've
written a BinaryReader and BinaryWriter mixin module, with methods like:

  read_word8(byte_order=ByteOrder::Native)
  read_word8_big ..._network
  read_word8_little 
  read_word8_native 

  and the same for word16, word32, int8, int16...

int's are signed integers, word are unsigned.

And to use it, you just have to extend your io object:

  require 'stringio'
  io = StringIO.new("Hello World")
  io.extend(BinaryReader)
  p io.read_word32

It's easy to add a unpack method:

  class BinaryReader
    def unpack(*spec)
      spec.map {|s| send("read_#{s}")} 
    end
  end
   
  io.unpack(:word8, :word8, :word32_little) 


Regards,

  Michael