Please tell me what this means? self.<method> in a class

ruby-talk
1

Not entirely sure I understand this (it's a newbie-ruby question).

class Test
  def foo
  end

  def Test.foo
  end

  def self.foo
  end
end

The first definitition of foo is an instance method. The second a
class method. Perhaps my terminology is wrong but I understand what I
mean.

It's the third one I'm not sure of. The "self.foo".

What does this do, how and where would I use it?

···

--

All the best
Glenn
Aylesbury, UK

2

The self.foo method definition is redefining Test.foo. It's kind of a
shorthand notation. You'd use by saying "Test.foo". The important lesson
here, is that class/module definitions are in fact executing ruby code in the
context of the class/module, hence, there is a "self" which is the
class/module object.

David

···

On Tuesday 29 March 2005 05:34 am, Glenn Smith wrote:

It's the third one I'm not sure of. The "self.foo".

What does this do, how and where would I use it?

3

Hello --

Not entirely sure I understand this (it's a newbie-ruby question).

class Test
def foo
end

def Test.foo
end

def self.foo
end
end

The first definitition of foo is an instance method. The second a
class method. Perhaps my terminology is wrong but I understand what I
mean.

It's the third one I'm not sure of. The "self.foo".

What does this do, how and where would I use it?

Every time you do this:

    def some_object.some_method
      ...
    end

you create a singleton method some_method for the object some_object
-- that is, a method that only some_object can call.

If you do the above using 'self' as the receiver, then the singleton
method you create will belong to whatever 'self' was at the time.

In your example, self is actually Test, the class whose scope you are
in. So, in effect, Test.foo and self.foo are the same, in that
context.

David

···

On Tue, 29 Mar 2005, Glenn Smith wrote:

--
David A. Black
dblack@wobblini.net

4

Ah. That's what confused me. I couldn't find it in pickaxe2.

Thanks David(s!)

Glenn

···

On Tue, 29 Mar 2005 20:11:01 +0900, David A. Black <dblack@wobblini.net> wrote:

Hello --

On Tue, 29 Mar 2005, Glenn Smith wrote:

> Not entirely sure I understand this (it's a newbie-ruby question).
>
> class Test
> def foo
> end
>
> def Test.foo
> end
>
> def self.foo
> end
> end
>
>
> The first definitition of foo is an instance method. The second a
> class method. Perhaps my terminology is wrong but I understand what I
> mean.
>
> It's the third one I'm not sure of. The "self.foo".
>
> What does this do, how and where would I use it?

Every time you do this:

    def some_object.some_method
      ...
    end

you create a singleton method some_method for the object some_object
-- that is, a method that only some_object can call.

If you do the above using 'self' as the receiver, then the singleton
method you create will belong to whatever 'self' was at the time.

In your example, self is actually Test, the class whose scope you are
in. So, in effect, Test.foo and self.foo are the same, in that
context.

David

--
David A. Black
dblack@wobblini.net

--

All the best
Glenn
Aylesbury, UK

5

Additional remarks:

- Preferably use "self" instead of the class name in order to minimize
the number of places in the code you have to touch if the class name
changes.

- You can as well use the class << notation either way

class Test
  class <<self
    def foo() "foo" end
  end

  class <<Test
    def bar() "bar" end
  end
end

Test.foo

=> "foo"

Test.bar

=> "bar"

Of course you can define multiple methods with this in one
class<<self...end like for "normal" classes.

Kind regards

    robert

6

There's more here:
http://www.rubygarden.org/ruby?SingletonTutorial

···

On Tue, Mar 29, 2005 at 08:29:34PM +0900, Glenn Smith wrote:

Ah. That's what confused me. I couldn't find it in pickaxe2.

Thanks David(s!)