From: Steven Jenkins <steven.jenkins@...>
Date: 2005-06-20T23:11:45+09:00
Subject: Re: preventing instantiation

R. Mark Volkmann wrote:
> Quoting Gavri Fernandez <gavri.fernandez@gmail.com>:
> 
> 
>>On 6/19/05, R. Mark Volkmann <mark@ociweb.com> wrote:
>>
>>>What is the recommended way in Ruby to prevent other classes from creating
>>>instances of a given class?  The class isn't a singleton.  It creates
>>
>>several
>>
>>>instances of itself and no additional instances should be able to be
>>
>>created.
>>
>>>I considered making the new method private, but thought there might be a
>>
>>better
>>
>>>way.
>>
>>What could be a better way than making new private? :)
>>The simplest solution is the best!
> 
> 
> When I put the following in my class, it seems that even that class can't create
> instances.
> 
> private_class_method :new
> 
> I'm confused.  How can I create a few objects within the class and then prevent
> other classes from creating additional instances?

Does this do it?

sjenkins@tidal ~ $ cat t.rb
require 'singleton'

class A; end

a0 = A.new
a1 = A.new
a2 = A.new

class A
  include Singleton
end

a3 = A.new
sjenkins@tidal ~ $ ruby t.rb
t.rb:13: private method `new' called for A:Class (NoMethodError)

Remember, 'include' is exectuable.

Steve