Ruby Syntax - One::Two

ruby-talk
1

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

2

Alle venerdì 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

3

I understand now, I didn't realize "class One::Two" actually defined
the constant Two inside One.
Thank you!

···

On Feb 16, 8:26 am, Stefano Crocco <stefano.cro...@alice.it> wrote:

Alle venerdì 16 febbraio 2007, tou...@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