From: Ryan Davis <ryand-ruby@...>
Date: 2011-03-10T08:06:30+09:00
Subject: Re: double singleton?


On Mar 9, 2011, at 14:34 , 7stud -- wrote:

> Roger Pack wrote in post #986564:
>> Hello all.
>> 
>> Noticed this behavior:
>> 
>>>> require 'singleton'
>> => true
>>>> class A; include Singleton; end
>> => A
>>>> A.instance
>> => #<A:0x3703c38>
> 
> I looked through the ruby docs and neither Object, Module, Class, nor 
> Singelton have a method named 'instance'.  Where does that come from?

9998 % ri Singleton
= Singleton

(from ruby core)
------------------------------------------------------------------------------
The Singleton module implements the Singleton pattern.

Usage:
       class Klass
          include Singleton
          # ...
       end

* this ensures that only one instance of Klass lets call it ``the instance''
  can be created.

  a,b  = Klass.instance, Klass.instance a == b   # => true a.new    # 
  NoMethodError - new is private ...

* ``The instance'' is created at instantiation time, in other words the first
  call of Klass.instance(), thus

          class OtherKlass
            include Singleton
            # ...
...