On 4/23/06, Michael Guterl <mgute= rl@gmail.com > wrote:

I finally decided to dive in and give m= etaprogramming in Ruby a shot. I'm not sure that my example is exactl= y 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 bett= er way?

3. I am using facets because I like the Dictionary (OrderedH= ash), but I'm sure there are better ways to build the structure while prese= rving the field order. I especially don't like the fact that I have t= o specify Dictionary[] in the structure of the subclass.

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

I'm not sure if it's customary to attach the code in a fil= e 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)
&nb= sp;
    class_eval do
      @@struct= ure =3D ordered_hash
    end

  &n= bsp; keys =3D @@structure.keys
    instance_eval do
&n= bsp;     attr_accessor *keys
    end<= br>
end

# this entire met= hod could probably be a lot cleaner

def self.open(file_name)
    class_eval do=
      data =3D IO.read(file_name)
&nb= sp;    records =3D []
      data= .each_line do |line|
        last_pos= ition =3D 0
        record =3D self.n= ew
        @@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
    &nbs= p;   end
        records &l= t;< record
      end
      re= turn records
    end
end

end

clas= s InputStructure < FixedLength

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

structur= e Dictionary[ :id , 10,
        = ;    :phone , 10,=20
            :fir= st_name , 25, :middle_name , 1, :last_name , 25,
   &nbs= p;        :address , 30,
  = ;          :city , 25,
&nb= sp;           :state , 2,=
            :zi= p , 5, :zip4 , 4 ]

end

require 'test/unit'

class InputStructureTest < Test::Unit::TestCase

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

def test_first
  &nbs= p; record =3D @records.first
    assert_equal "1&quo= t;,=20 record.id
    assert_equ= al "1234567890", record.phone
    assert_equal = "SOME RANDOM", record.first_name
    assert_equal "", record.middle_name
&nb= sp;   assert_equal "PERSON",=20 record.last_name
    assert_equal "1234 SOME RANDOM = STREET", record.address
    assert_equal "RANDO= M CITY", record.city
    assert_equal "OH"= , record.state
    assert_equal "45219",=20 record.zip
    assert_equal "", record.zip4
= end

end