anonymous classes

[Ian Macdonald]

Hi,

Could someone please explain to me the concept of an anonymous class?

I'm talking about this construct:

class << Foo
...
end

I'm having a hard time understanding the books and figuring out when I
might actually want/need to use this.

Ian
--
Ian Macdonald | Keep cool, but don't freeze. -- Hellman's
System Administrator | Mayonnaise
[email]ian@caliban.org[/email] |
[url]http://www.caliban.org[/url] |
|

[Chad Fowler]

Ian Macdonald wrote:

>Hi,
>
>Could someone please explain to me the concept of an anonymous class?
>
>I'm talking about this construct:
>
>class << Foo
>...
>end
>
>I'm having a hard time understanding the books and figuring out when I
>might actually want/need to use this.
>
>Ian
>
>

This may be a good starting point:

[url]http://www.rubygarden.org/ruby?ClassMethods[/url]

Chad

[Ian Macdonald]

On Tue 01 Jul 2003 at 19:04:23 +0900, Brian Candler wrote:

> On Tue, Jul 01, 2003 at 08:50:31AM +0900, Ian Macdonald wrote:

> > Hi,
> >
> > Could someone please explain to me the concept of an anonymous class?
> >
> > I'm talking about this construct:
> >
> > class << Foo
> > ...
> > end
> >
> > I'm having a hard time understanding the books and figuring out when I
> > might actually want/need to use this.

>
> What you've written is called a "singleton class". I wrote this a while:
>
> [url]http://www.rubygarden.org/ruby?SingletonTutorial[/url]
>
> It might be helpful and includes a couple of links to more detailled
> information.

Thanks. This is an excellent resource and makes things a lot clearer.

Ian
--
Ian Macdonald | Yes, we will be going to OSI, Mars, and
System Administrator | Pluto, but not necessarily in that order.
[email]ian@caliban.org[/email] | -- Jeffrey Honig
[url]http://www.caliban.org[/url] |
|

[Dominik Werder]

> What you've written is called a "singleton class". I wrote this a while:

>
> [url]http://www.rubygarden.org/ruby?SingletonTutorial[/url]

it is very helpful for me too :)

One question referring to
"A neat solution then is to create a singleton class for each POP3
connection as it arrives: "
How much memory does this technique consume? Are the new methods created
for each individual instance? Or just something like a lookup table?

bye!
Dominik

[Brian Candler]

On Wed, Jul 02, 2003 at 05:36:21PM +0900, Dominik Werder wrote:

> > What you've written is called a "singleton class". I wrote this a while:
> >
> > [url]http://www.rubygarden.org/ruby?SingletonTutorial[/url]

>
>
> it is very helpful for me too :)
>
> One question referring to
> "A neat solution then is to create a singleton class for each POP3
> connection as it arrives: "
> How much memory does this technique consume? Are the new methods created
> for each individual instance? Or just something like a lookup table?

All that happens is that a new proxy class is added to the object, which
points at the module which you #extended it with. It certainly doesn't copy
all the methods.

You can prove this easily enough, by modifying the module *after* you have
done extend:

module A
end
a = "hello"
a.extend A
b = "world"
b.extend A

module A
def foo
puts "it works"
end
end
a.foo #=> "it works"
b.foo #=> "it works"

You can see that the two objects share the same module implementation.

Regards,

Brian.