From: Robert Klemme <shortcutter@...>
Date: 2010-09-13T23:21:46+09:00
Subject: Re: Converting from one class to another in Ruby

On Sun, Sep 12, 2010 at 3:34 AM, Harry Spier <harryspier@hotmail.com> wrote:
> Dear list members,
>
> I have an application with a class Binary_matrix < Array (which is just

The first thing I'd do differently is to cut off this inheritance.
Inheriting from core classes is rarely a good idea.  In this case you
*use* an array for your storage of a binary matrix which is an
implementation detail that should be hidden inside the class.  Also I
am sure you do not want all public Array methods to be available for
users of Binary_matrix.  So delegation is a much better option here.

> a two dimensional array filled with zeroes and ones).  I also have other
> classes which have to_Binary_matrix methods to convert objects of their
> class to Binary_matrix objects.
>
> The Ruby code I came up with to do the conversions is as follows.
>
> class A
>  def to_Binary_matrix(from_initialize_method = false)
>     ...some logic to convert class A object to binary_matrix_format
>     if from_initialize_method
>        return an_A_type_object_in_binary_matrix_format
>    else
>        return
> Binary_matrix.new(an_A_type_object_in_binary_matrix_format)
>    end
>  end
> end

I find it hard to come up with good suggestions since a lot is missing
in this example (for example how you call it from #initialize).  Why
don't you have a method
some_logic_to_convert_class_A_object_to binary_matrix_format which is
then called from #initialize and from to_Binary_matrix?  That seems
the most natural solution and then you do not need the flag in the
first place.

> class B
>  def to_Binary_matrix(from_initialize_method = false)
>     ...some logic to convert class B object to binary_matrix_format
>     if from_initialize_method
>        return a_B_type_object_in_binary_matrix_format
>    else
>        return
> Binary_matrix.new(a_B_type_object_in_binary_matrix_format)
>    end
>  end
> end
>
> class Binary_matrix < Array
>   def initialize arg
>      self.replace arg.to_Binary_matrix(true)
>   end
> end
>
> This allows me to do:
>
> a = A.new
> an_A_as_a_Binary_matrix_object = a.to_Binary_matrix
> b_as_a_Binary_matrix_object = Binary_matrix.new(b)
>
> It works but it seems a little clunky to me.  Is their a more Rubyish or
> elegent way of doing this.  In particular is it possible to get rid of
> the flag I use (from_initialize_method) to keep me from getting into an
> infinite loop as I go between the .to_Binary_matrix methods and the
> initialize method in Binary_matrix

It looks absolutely clunky.

Kind regards

robert

-- 
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