BufferMapper provides lazy-loading bindings for a binary buffer

buffer_mapper.rb

module Raumod::BufferMapper
  # See http://ruby-doc.org/core/classes/String.html#M001112
  # for map types.
  
  def data_map;@data_map;end
  def data;@data;end
  def data_entry(method)
    offset = data_map[method][:offset]
    type = data_map[method][:type]    
    d = data[offset..-1].unpack(type)
    if d.count > 1
      d
    else
      d.first
    end
  end
  def method_missing(method,*args)      
    if data_map[method]
      data_entry(method)
    else
      raise "No such method: #{method}"
    end
  end    
end

module.rb

class Raumod::XM::Module
  require 'buffer_mapper'
  include Raumod::BufferMapper
  
  HeaderMap = { 
    :id_text=>{ :offset=> 0, :type=>'A17'},
    :name=>{:offset=>17,:type=>'A20'},
    :'1a' => {:offset=> 37, :type=>'C'},
    :tracker_name=>{:offset=>38,:type=>'A20'},
    :version=> {:offset=> 58, :type=> 'v'},
    :header_size=>{:offset=> 60,:type=>'V'},
    :song_length=>{:offset=> 64,:type=>'v'},
    :restart_position=>{:offset=> 66 ,:type=>'v'},
    :channel_count=>{:offset=> 68 ,:type=>'v'},
    :pattern_count=>{:offset=> 70 ,:type=>'v'},
    :instrument_count =>{:offset=> 72 ,:type=>'v'},
    :flags =>{:offset=> 74 ,:type=>'v'},
    :default_tempo=>{:offset=> 76 ,:type=>'v'},
    :default_bpm=>{:offset=> 78 ,:type=>'v'}
  }

  attr_accessor :patterns,:instruments
  def initialize(data=nil)
    @data= data #|| "Extended Module: "
    @data_map = HeaderMap
  end
end