From: Austin Ziegler <halostatue@...>
Date: 2005-12-07T14:20:06+09:00
Subject: Re: how best to handle errors in object instaintiation (sp ?)

On 12/5/05, Timothy Hunter <cyclists@nc.rr.com> wrote:
> Russell Fulton wrote:
> > Hi,
> >    I'm new to Ruby and still trying to figure out how best to do things
> > "the Ruby way".  The particular problem I am looking at now is the
> > initialize method of a class I am writing. Several things can go wrong
> > in calls to new for this class ranging from the caller specifying
> > incompatible parameters to database calls failing.
> >
> > What is the perferred method of handling such errors? Simply raising
> > exceptions and returning nil?
> You don't really have any choice. The return value from 'new' is an
> instance of the class, never nil. (Okay, some clever Rubyists could
> think of a way to make it nil, but no user of your class should ever be
> asked to handle that case.) If your initialize method can fail, it
> should raise an exception.

Hm, no, that's not quite right ;)

  class Foo
    def self.new
      super
    rescue Exception
      nil
    end
    def initialize
      raise "Bah!"
    end
  end

It's not ideal, and it would probably be better to do something like:

  class Bar
    class << self
      private :new

      def create(*args, &block)
        ob = self.allocate
        ob.initialize(*args, &block)
        ob
      rescue Exception
        nil
      end
    end
    def initialize(*args, &block)
      raise "Empty!" if args.empty
      @args = args
    end
    attr_accessor :args
  end

That is, it's better to use a different method than new.

-austin
--
Austin Ziegler * halostatue@gmail.com
               * Alternate: austin@halostatue.ca