From: Stefano Crocco <stefano.crocco@...>
Date: 2007-02-16T19:26:25+09:00
Subject: Re: Ruby Syntax - One::Two

Alle venerd� 16 febbraio 2007, toulax@gmail.com ha scritto:
> I'm a newcomer to ruby and there's this little something I don't
> really understand:
>
> class One::Two
> ...
> end
>
> Class One::Three
> ...
> end
>
> On this example, what does "::" mean? If understand correctly it's
> just sort of a naming convention to imply that both the Two and Three
> classes belong to the same "group", as in Net::HTTP and Net::FTP.
> So, in essence Two and Three are completely unrelated, and I'd not
> even need to have a class named One for it to work, is that right?
>
> If not, please tell me, what exactly is the purpose of "::" on class
> names?
>
> Thanks

:: is the scope operator. It is used to access constants defined in a class or 
module. Since classes are constants, when you write class One::Two, you're 
defining the class Two inside One (where One can be a class or a module). If 
you didn't define One, the code class One::Two will give you a NameError, 
telling you that the constant One is not initialized:

>> class One::Two
>> end
NameError: uninitialized constant One
        from (irb):1
>>

Another example of the use of :: is 

puts Math::PI, which prints the value of the PI constant

>> puts Math::PI
3.14159265358979

Since PI belongs to the Math module, I couldn't have written puts PI. In fact, 
this raises an exception:

>> puts PI
NameError: uninitialized constant PI
        from (irb):5

I hope this helps.

Stefano