From: Harry Spier <harryspier@...>
Date: 2010-09-15T00:58:00+09:00
Subject: Re: Converting from one class to another in Ruby

Robert Klemme wrote:

>  Just do this for your classes:
> 
> class A
>   def initialize( what goes here? )
>     # what do you want to do here?
>   end
> 
>   def to_binary_matrix
>     bm = BinaryMatrix.new
>     # fill bm
>     bm
>   end
> end
> 
> 
>> Rather I wanted my Binary_matrix object to check if the object to be
>> converted to a Binary_matrix had a to_Binary_matrix method and then to
>> call it.
> 
> Just call it (see below).
> 

> Why and what do you want to convert to BM in #initialize?  This hasn't
> become clear yet.

I wrote
>> I want to be able to say
>> page_in_pixels = page_image.to_Binary_matrix
>> as well as
>> page_in_pixels = Binary_matrix(page_image)
> 

I meant to write: (more finger trouble :-)  )
I want to be able to do both:
page_in_pixels = page_image.to_Binary_matrix
page_in_pixels = Binary_matrix.new(page_image)
(i.e. Binary_matrix.new doesn't create an empty Binary_matrix object but 
takes as a parameter an object which is converted to a Binary_matrix )

so for that reason my solution had as follows:
1) obj_a.to_Binary_matrix calls Binary_matrix.new to create a new 
Binary_matrix object.
I.e.In this case  #to_Binary_matrix is being called outside the context 
of Binary_matrix#initialize

but

2)Binary_matrix#initialize contains an arg = arg.to_Binary_matrix 
statement to access the conversion logic.
I.e. #to_Binary_matrix is being called within the context of 
Binary_matrix#initialize

 so my solution (retyped at the end of this post had a flag to keep from 
getting in an infinite loop and to do the following:

(I'm not sure if I'm missing something really obvious but I still don't 
see that I don't need a flag or someway to tell if #to_Binary_matrix is 
being called within Binary_matrix#initialize or not)

case 1:
p = page_image.to_Binary_matrix
   calls page_image.to_Binary_matrix
    --> calls Binary_matrix.new(page_image) since flag_not_set
           Binary_matrix.initialize(arg)
             arg = arg.to_Binary_matrix(flag_set)
               -->calls arg.to_Binary_matrix(flag_set)
                    convert page_image to binary format since flag_set
           Binary_matrix <-- return binary matrix format since flag_set
    <-----Binary_matrix.new returns Binary_matrix obj

case 2:
p = Binary_matrix.new(page_image)
  calls Binary_matrix.new(page_image)
  --> Binary_matrix.initialize(arg)
        arg = arg.to_Binary_matrix(flag_set)
             -->calls arg.to_Binary_matrix(flag_set)
                -->calls arg.to_Binary_matrix(flag_set)
                    convert page_image to Binary_matrix format since 
flag_set
           Binary_matrix <-- return binary matrix format
    <-----Binary_matrix.new returns Binary_matrix obj




 class Binary_matrix < Array
    def initialize(arg)
      called_from_initialize =true
      if arg.respond_to? :to_Binary_matrix
        arg = arg.to_Binary_matrix (called_from_initialize)
      else
       ....do some error reporting
      end
      validate arg #Is the Binary_matrix object correctly formed?
       self.replace arg
    end
 ...
 end


 class A
    def to_Binary_matrix(from_initialize_method = false)
       if from_initialize_method
           ...logic to convert to Binary_matrix format
           and store result in two_dimensional_binary_array...
          return two_dimensional_binary_array
         else
          return Binary_matrix.new(self)
       end
     end
 ...
 end

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