7 Languages in 7 weeks: Ruby day 3

Ruby Day 3: Serious change 

The final day on Ruby is all about metaprogramming. It takes you through:

• Adding methods to open classes
• Using method missing to produce very human readable syntax
• Adding functionality to classes via Modules

Having used Java reflection, Java IDL Dynamic Invocation Interface (DII) and the Java IDL Dynamic Seketon Interface extensively when I used to develop IBM's Websphere Message Broker I know how cumbersome any form of metaprogramming is in Java. So I enjoyed playing around with a language that does it much better!

Now to the Self study. Only one this time! Modify the Csv application to support an each method to return a CsvRow object. E.g for the following csv file:

one, two

lions, tigers

allow an API that works like this:

csv = RubyCsv.new

csv.each{|row| puts row.one}

This should print "lions".

Well I decided to work with the following input:

one, two, three

1, 2, 3 

uno, dos, tres

And here is my solution using modules and method missing:

module ActsAsCsv

  def self.included(base)

    base.extend ClassMethods

  end

  module ClassMethods

    def acts_as_csv

      include InstanceMethods

    end

  end

  module InstanceMethods

    def read

      @csv_contents = []

      filename = self.class.to_s.downcase + '.txt'

      file = File.new(filename)

      @headers = file.gets.chomp.split(', ')

      file.each  do |row|

        @csv_contents << row.chomp.split(', ')

      end

    end

    def each(&block)

      @csv_contents.each_index do |index|

        hash = Hash[@headers.zip @csv_contents[index]]

        block.call(CsvRow.new(hash))  

      end

    end

  end

  attr_accessor :headers, :csv_contents

  def initialize

    read

  end

end

class RubyCsv

  include ActsAsCsv

  acts_as_csv

end

class CsvRow

  def initialize(arg)

    @arg = arg

  end

  

  def method_missing name, *args

    key = name.to_s

    return @arg[key]

  end

end

m = RubyCsv.new

m.each do |row| 

  puts row.send(ARGV[0])

end

And that is it for Ruby!