From: Michael Guterl <mguterl@...>
Date: 2006-04-23T13:07:34+09:00
Subject: Metaprogramming is fun!

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I finally decided to dive in and give metaprogramming in Ruby a shot.  I'm
not sure that my example is exactly practical, but it seemed useful at the
time.  There's a few areas I would like to hear others suggestions on:

1. Does the syntax appear to be in line with the community standards?

2. Are my uses of class_eval and instance_eval okay / is there a better way=
?

3. I am using facets because I like the Dictionary (OrderedHash), but I'm
sure there are better ways to build the structure while preserving the fiel=
d
order.  I especially don't like the fact that I have to specify Dictionary[=
]
in the structure of the subclass.

4. Please comment on the code in general, I'm open to any kind of criticism=
.

I'm not sure if it's customary to attach the code in a file or post it in
the email.  I apologize if I should have attached the code in a file.

Michael Guterl

----------------------------------------------

require 'rubygems'
require 'facets'
require 'dictionary'

class FixedLength

  def self.structure(ordered_hash)

    class_eval do
      @@structure =3D ordered_hash
    end

    keys =3D @@structure.keys
    instance_eval do
      attr_accessor *keys
    end

  end

  # this entire method could probably be a lot cleaner

  def self.open(file_name)
    class_eval do
      data =3D IO.read(file_name)
      records =3D []
      data.each_line do |line|
        last_position =3D 0
        record =3D self.new
        @@structure.each_pair do |name, length|
          record.instance_variable_set( "@#{name.to_s}",
line.slice(last_position,
length.to_i).strip)
          last_position +=3D length.to_i
        end
        records << record
      end
      return records
    end
  end

end

class InputStructure < FixedLength

  # I'd like to clean this up, either removing the need for Dictionary[] an=
d
the separation by commas
  # or with something like this
  # column.add :id, 10
  # column.add :phone, 10
  # column.add :first_name, 25
  # etc.  I'd love to hear some suggestions.

  structure Dictionary[ :id , 10,
            :phone , 10,
            :first_name , 25, :middle_name , 1, :last_name , 25,
            :address , 30,
            :city , 25,
            :state , 2,
            :zip , 5, :zip4 , 4 ]

end

require 'test/unit'

class InputStructureTest < Test::Unit::TestCase

  def setup
    @records =3D InputStructure.open('fixed_data.txt')
  end

  def test_first
    record =3D @records.first
    assert_equal "1", record.id
    assert_equal "1234567890", record.phone
    assert_equal "SOME RANDOM", record.first_name
    assert_equal "", record.middle_name
    assert_equal "PERSON", record.last_name
    assert_equal "1234 SOME RANDOM STREET", record.address
    assert_equal "RANDOM CITY", record.city
    assert_equal "OH", record.state
    assert_equal "45219", record.zip
    assert_equal "", record.zip4
  end

end

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