From: bwv549 <jtprince@...>
Date: 2007-04-04T02:15:12+09:00
Subject: Re: implementing an array based class

Based on the model I was using above for an array based object
(inherits from array) and similar to the way Struct works to
initialize it, I've worked up this guy (with some effor):


class ArrayClass
  def self.create(fields)
    new_class = Class.new(Array)
    new_class.class_eval('undef_method :flatten')
    new_class.class_eval('undef_method :flatten!')
    new_class.class_eval("@@keyword_to_index = {}")
    fields.each_with_index do |field,i|
      field_sym = field.to_sym
      ## THE GETTERS AND SETTERS:
      new_class.class_eval("def #{field}() self[#{i}] end")
      new_class.class_eval("def #{field}=(val) self[#{i}]=val end")

      new_class.class_eval("@@keyword_to_index[:#{field}] = #{i}")
    end
    new_class.class_eval('def self.indices() @@keyword_to_index end')
    new_class.class_eval('def indices() @@keyword_to_index end')
    new_class
  end
end

## 'flatten' wreaks havoc on objects that inherit from array.  I've
tried in different ways to make the above object insensitive to
flatten, with no real luck.  It will break code with other array-based
objects that want to be flattened, but allows us to use flatten on
arrays of our objects:

class Array
  ## WARNING! I've redefined Array#flatten to only work on Array
objects (not
  # derived objects)
  def flatten
    new_array = []
    self.each do |v|
      if v.class == Array
        new_array.push( *(v.flatten) )
      else
        new_array << v
      end
    end
    new_array
  end

  ## WARNING! I've redefined Array#flatten! to only work on Array
objects (not
  # derived objects)
  def flatten!
    self.replace(flatten)
  end
end

## USAGE:
MyClass = ArrayClass.create( %w(f1 f2 f3 f4 f5) )
obj = MyClass.new( %w(v1 v2 v3 v4 v5) )
puts obj.f1
obj.f2 = 'something_else'
MyClass.indices # -> hash giving index based on keyword.
obj.indices     # -> same

I've written some tests and it seems to fly.