From: Phrogz <gavin@...>
Date: 2007-06-07T05:00:13+09:00
Subject: Re: best DRY solution for this task

On Jun 6, 11:57 am, anansi <kaz...@oleco.net> wrote:
> I'm reading a file byte for byte. This file is structured and I try to
> give out each structures element and the meaning of it. So let's pretend
> the file content would be this in bytes (you get it e.g. with
> file.read(7)): 1 3d 0 233 0 1 2f

a) You might want to look into the BitStruct library.
b) See the following. It's up to you how much work you want to put in
the common 'eat' method, versus how much you want to leave up to the
proc for each particular matcher.

# Just for no-file testing
require 'stringio'
bytes = [ 1, 0x3d, 0, 233, 0, 1, 0x2f  ]
byte_string = StringIO.new( bytes.map{ |b| b.chr }.join )

class ByteEater
  def initialize( title, num_bytes, &block )
    @title = title
    @num_bytes = num_bytes
    @proc = block
  end
  def eat( file )
    bytes = file.read( @num_bytes )
    print( "#@title: " )
    @proc.call( bytes )
    bytes.each_byte{ |x| print "%x" % x }
    puts ""
  end
end

structure = [
  ByteEater.new( 'startflag', 3 ){ |bytes|
    if bytes == "\01\x3d\0"
      print " good"
    else
      print " bad"
    end
  },
  ByteEater.new( 'dbg_mode', 1 ){ |bytes|
    case bytes
      when 1.chr
        print " on"
      when 255.chr
        print "don't know"
      else
        print "bad"
    end
  },
]

structure.each{ |eater|
  eater.eat( byte_string )
}

#=> startflag:  good13d0
#=> dbg_mode: bade9