From: Martin Hansen <mail@...>
Date: 2010-04-16T21:33:16+09:00
Subject: Writing a parser

Hello there,

I am struggling to get a grip on OO (and Ruby) and write a parser for
this particular data format described at the below get_record method.
The goal is to parse and emit records of this type and be able to
manipulate these with the methods in class Hash.

For now I am trying to get parsing to work, and the problem here is,
that the add methods is not defined for Hash. What is the best way of
doing that?



M




class Record < Hash
  SEPERATOR = "\n---\n"

  def initialize(path=nil)
    @path = path
    @ios  = File.open(@path, 'r') if @path
  end

  # Reads the next 'record' from the I/O stream. The records are
separated by
  # lines of "---" and each record consists of a varying number of lines
with a
  # key/value pair separated by ": ". The record is returned as a hash.
  def get_record
    block = @ios.gets(SEPERATOR).chomp!(SEPERATOR)

    record = {}
     block.each_line do |line|
      fields = line.split(": ")
      raise ArgumentError, "Bad record line: #{line}" if fields.length
!= 2

      record.add(fields[0],fields[1])
    end

    record
  end

  # Add a key value pair to this record.
  def add(key, value)
    raise ArgumentError, "Bad key contains ': ' or '\n' ->#{key}"     if
key.match(": |\n")
    raise ArgumentError, "Bad value contains ': ' or '\n' ->#{value}" if
value.match(": |\n")

    self[key] = value
  end

  # Return the content of this record as a string.
  def to_s
    return nil if empty?
    self.map { | key, val | "#{ key }: #{ val }" }.join( "\n" ) +
SEPERATOR
  end
end
-- 
Posted via http://www.ruby-forum.com/.