So, let's talk about Ruby...

[Huw Collingbourne]

...and maybe some Rails too.  

This is the place to ask questions and share ideas about Ruby programming in general. If you are a newcomer to Ruby, you might be interested in downloading our free eBook, The Little Book Of Ruby, to help to get you started. For a more in-depth guide, download The Book Of Ruby.

Please bear in mind that this forum is intended for users of SapphireSteel Software IDEs so please confine discussion to programming issues related to Ruby In Steel and/or the two SapphireSteel Software Ruby eBooks mentioned above.

best wishes
Huw

[papp.zoltan]

I don't understand singleton methods. There is a same name but different meanings in Design Patterns.

[Huw Collingbourne]

I've explained these in the Book. Can you tell me which elements you don't understand?

Best wishes

Huw

[papp.zoltan]

In Desing Patterns, singleton object mean there is only one and nothing more object created.
http://en.wikipedia.org/wiki/Singleton_pattern

If you understand Java here is the sample:

class Singleton
{
   private static Singleton instance;
   private Singleton()
   {
      ...
   }

   public static synchronized Singleton getInstance()
   {
      if (instance == null)
         instance = new Singleton();

      return instance;
   }
   ...
   public void doSomething()
   {
      ...   
   }
}

Singleton.getInstance().doSomething();

[Huw Collingbourne]

I think that's similar to Ruby singletons. But in Ruby singleton is 'built in' to the language so you don't have to check if an instance exists before creating a singleton. The only confusing thing in Ruby is that there are several syntaxes for creating Singletons and singleton methods.

Singleton methods are methods that can be added to a specific object. So if you have class X and objects x1 and  2 you can add method y() to x2 but x1 won't have it.

A singleton class is a class which is used to create a single object. e.g.

Code:

ob = Object.new
  class << ob
    def blather( aStr )
      puts("blather, blather #{aStr}")
    end
  end

Here the unnamed class descends from object, defines methods etc in the usual way and adds them to the object called ob. Now ob is the only object with those methods. No other instance can be created from the class so it is a singleton. As I said there are other syntaxes too but fundamentally that's how singletons work in Ruby.

best wishes

Huw

[ArunSakthivel]

If you want to mare information about singleton check this link
http://dalibornasevic.com/posts/9-ruby-singleton-pattern-again

[petermmose]

I have read your book, It was really very easy simple to understand and very informative also. It helped me a lot to understand the most powerful mix-in Functionality of ruby.