From: James Ponder <james@...>
Date: 2001-04-24T00:55:52+09:00
Subject: [ruby-talk:14080] Re: OO

On Mon, Apr 23, 2001 at 09:42:42AM +0900, chad fowler wrote:
> What kind of data will be stored in the "Options"
> object?  What do the individual classes need from it? 
> It sounds like you are creating a static configuration
> mechanism.  Another coupling-related fear that I would
> have is that, when you pass a full "Options" into an
> object, you are probably giving that object access to
> any of the data in "Options".  So, you're creating
> possible dependencies between every object that uses
> "Options" and every possible "Option".

I think I understand what you are saying, but I don't see how I can achieve
this in practice.  For example, my options file might contain "debug=1",
and I don't want to have to alter my classes each time I come up with a new
option that several classes need to know about.

I've been discussing this with some Java people, and they think I should
be using a "singleton" - although this word appears to be used in Ruby as
a way of adding methods to objects I've not seen it used in the same way
that Java people use it.  Apparently in Java you do this by creating
a private constructor (so that nobody can instantiate the class) and have a
class variable that holds one instance of the object.  The object is normally
instantiated in the class init code or in a "unless(obj) obj = MyClass.new()"
way within each class method.

In Ruby, can you stop someone being able to instantiate an object?

> The solution I would propose is that you keep
> "Options" outside of any objects that don't
> specifically need it.  Then, from a controller object
> (probably the same one that actually instantiates each
> object), you can read "Options" and pass any required
> data to the objects that need it.  With this approach,
> "Options" doesn't know about your objects, and your
> objects don't know about "Options".

To me, if I add an option that is applicable to one particular class, it
seems bad that I have to alter the controller code, the class code
AND the constructor.

Or am I still thinking about this in the wrong way?


Best wishes, James
-- 
James Ponder; www.squish.net