From: Albert Wagner <alwagner@...>
Date: 2002-01-10T12:41:26+09:00
Subject: Re: How to override subclass#new

Nevermind.  I've solved my own problem. 

 	class A
 	    def A.new(a, *args)
 	    end
 	end

 	class B < A
	    @@b = nil
	    @@c = nil
 	    def B.new(a, b, c)
	        @@b = b
	        @@c = c
 	        x = 1
 	        y = 2
 	        z = 3
 	        <more>
 	        super(a, *args)
 	    end
 	    def initialize(a, *args)
 	        @a = a
 	        @b = @@b
 	        @c = @@c
 	    end
 	end

 	B.new(a,b,c)	#<==preferred method of creating a B instance

It still feels like a kludge, but it works.  

For those who questioned why and offered no how:  you learn by doing; There 
is no better reason.

But in fact, it wasn't "new" that I was adding behaviour to, but rather 
"create" and "open", aliases for "new".  "A" is a c code extension of a file 
manager(BDB).  x, y, z, and etc  are a variable number of attributes that 
determine, among other things, whether a new file is to be created or an 
existing file is to be opened for update.  I wanted to subclass "A" so that I 
could embed code to convert a Ruby Struct to delimited string format for 
persistent storage in the database. (Unlike relational DBs, Berkely DB does 
not keep track of fields; a record is just a binary string of arbitrary 
length)  I wanted this "catalog" type info to be contained in the file object 
and entered only once.  I also disliked the ugliness of a long string of file 
attributes cluttering up my main code.  Additionally, with eveything 
pertaining to a file properly contained in the file object, I was able to 
override the [] and []= methods of the "A" file object, so that I could 
interject code to format/unformat records cleanly.  I can now do code like 
this for the file catalog:

		if File.exists?(@catName + '.bdb')
			@cat = Catalog.open(@catName)
		else
			@cat = Catalog.create(@catName)
		end

		@cat[fileName] = fileFieldListAndOtherFileInfo  

		fileFieldListAndOtherFileInfo = @cat[filename]

And identical functionality for the data files.

This is much cleaner.  And it greatly pleases me.		

-- 
Quantum Mechanics: The dreams stuff is made of