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-   -   self in method name (http://www.velocityreviews.com/forums/t841481-self-in-method-name.html)

iskaldur 06-12-2007 04:19 AM

self in method name
 
Is there any difference between using self in a method name, and not
using it?
For example, I've seen a lot something like

class Foo
def self.bar
...
end
end

Is this the same thing as

class Foo
def bar
...
end
end
?

--
Posted via http://www.ruby-forum.com/.


Jeremy McAnally 06-12-2007 05:22 AM

Re: self in method name
 
The first one creates a class method as opposed to the second one that
creates an instance method (e.g., Foo.bar rather than x = Foo.new;
x.bar;). :)

--Jeremy

On 6/12/07, iskaldur <iskaldur@gmail.com> wrote:
> Is there any difference between using self in a method name, and not
> using it?
> For example, I've seen a lot something like
>
> class Foo
> def self.bar
> ...
> end
> end
>
> Is this the same thing as
>
> class Foo
> def bar
> ...
> end
> end
> ?
>
> --
> Posted via http://www.ruby-forum.com/.
>
>



--
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My free Ruby e-book:
http://www.humblelittlerubybook.com/book/

My blogs:
http://www.mrneighborly.com/
http://www.rubyinpractice.com/


dblack@wobblini.net 06-12-2007 10:46 AM

Re: self in method name
 
Hi --

On Tue, 12 Jun 2007, iskaldur wrote:

> Is there any difference between using self in a method name, and not
> using it?
> For example, I've seen a lot something like
>
> class Foo
> def self.bar
> ...
> end
> end
>
> Is this the same thing as
>
> class Foo
> def bar
> ...
> end
> end


def self.bar is just a special case of:

def some_object.some_method

i.e., defining a singleton method on an object (a method that exists
only in the method look-up for that particular object, not for other
objects of its class). Actually it's not even a special case; it's
just using the current value of self as the object on which to define
the method.

At the top level of a class definition block, self is the class object
-- in this case, Foo. A singleton method defined on a class object
(such as Foo.bar) is usually referred to as a class method. In
addition, class methods are special-cased a bit, in comparison with
other singleton methods... but that's Lesson Two :-)


David

--
* Books:
RAILS ROUTING (new! http://safari.awprofessional.com/9780321509246)
RUBY FOR RAILS (http://www.manning.com/black)
* Ruby/Rails training
& consulting: Ruby Power and Light, LLC (http://www.rubypal.com)


Bertram Scharpf 06-12-2007 11:08 AM

Re: self in method name
 
Hi,

Am Dienstag, 12. Jun 2007, 13:19:02 +0900 schrieb iskaldur:
>
> class Foo
> def self.bar
> ...
> end
> end
>
> Is this the same thing as
>

class Foo
class <<self
def bar
...
end
end
end


Bertram


--
Bertram Scharpf
Stuttgart, Deutschland/Germany
http://www.bertram-scharpf.de


Peter Cooper 06-12-2007 11:18 AM

Re: self in method name
 
On 6/12/07, Bertram Scharpf <lists@bertram-scharpf.de> wrote:
> > class Foo
> > def self.bar
> > ...
> > end
> > end

>
> Is this the same thing as
>
> class Foo
> class <<self
> def bar
> ...
> end
> end
> end


Yes, except in the second you're actually opening up the virtual class
to work on it directly whereas in the first example you're defining
the method using an absolute name.

It's easy to see this as a pattern though without understanding the
background, which, hopefully, a brief example will rectify:

class << Fixnum
def x; "y"; end
end

puts Fixnum.x # => "y"
puts 10.x # ERROR

Note that you can dig into virtual classes at any time, not just
within the capacity of a class you're currently defining :)

So.. when you see class << self within the definition of another
class, then it's the equivalent of class << ClassName, and merely
using the "self" to provide the current class rather than naming it
explicitly.

Cheers,
Peter Cooper
http://www.rubyinside.com/


Erik Veenstra 06-12-2007 04:10 PM

Re: self in method name
 
> class Foo
> def self.bar
> end
>
> def bar
> end
> end


Arguably, the equivalent in Java is this:

public class Foo {
public static void bar1() {
}

public void bar2() {
}
}

Notice that you can't use the same method name statically and
as instance method in Java, whereas you can use the same name
for the class method and the instance method in Ruby.

gegroet,
Erik V. - http://www.erikveen.dds.nl/




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