From: Richard Turner <richard@...>
Date: 2005-01-21T23:58:55+09:00
Subject: Re: Refernce objects

On Fri, 2005-01-21 at 23:36 +0900, David A. Black wrote: 
> >
> > I'm new to Ruby
> 
> Welcome!
> 

Thank you :)

> 
> At the risk of over-simplifying, let me try to simplify :-)
> 
> Generally in Ruby you don't need or see too many methods with 'get'
> and 'set' in their names, since there are a variety of ways to perform
> those operations less verbosely.  For example, you can define a method
> called [] and then use index-style bracket syntax:
> 
>    class Section
>      def self.[](n)
>        # here, a fetch command for record n
>      end
>    end
> 
>    record = Section[10]
> 
> That would bypass the need for a constructor (if that's appropriate in
> your case).
> 

That's great, but isn't that just a more succinct way of doing the same
thing?  I.e. isn't this the same?:

class Section
  def self.loadedFromDB(sectionID)
    # here, a fetch command for record sectionID 
  end
end

What I want []() or loadedFromDB() to return is a Section, but I don't
want people to be able to call Section.new in error, otherwise they'll
not get what they think.  E.g.:

secFromFactory1 = Section.getSection(10)
=> #<Section:0xb7f8d468 @index=1, @firstQuestionID=515, @name="Living
Arrangements", @sectionID=10>
secFromFactory2 = SectionFactory.getSection(10)
=> #<Section:0xb7f8d468 @index=1, @firstQuestionID=515, @name="Living
Arrangements", @sectionID=10>

BUT:
secFromNew = Section.new(10)
=> #<Section:0xb7f728e8 @index=1, @firstQuestionID=515, @name="Living
Arrangements", @sectionID=10>

See the object IDs are the same from the factory but different using the
constructor.  So if I do:

secFromFactory1.index = 2
secFromFactory2.index
=> 2
BUT:
secFromNew.index
=> 1

In short, I've rather painfully created a factory method that, given an
ID, returns the correct object from a pre-filled set.  However, I now
need to stop people using Section.new and I can't.  This leads me to
believe that there may be a Better Way, but I don't know what it is :(

Cheers,

Richard.