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comp.lang.ruby

Mixin a module method as a class method

Farrel Lifson

10/18/2006 1:05:00 PM

Is it possible to mix in a module method to become a class method? I'd
like to define the method_added method in a module and then mix it
into a class like so
module Foo
def self.method_added(method)
puts "Added #{method}"
end
end

class Bar
include Foo
def bar
end
def baz
end
end
So that I get
Added bar
Added baz
printed out. Is there any way to do this besides making Foo a class
and subclassing Foo from it?

Farrel
9 Answers

Jano Svitok

10/18/2006 1:19:00 PM

0

On 10/18/06, Farrel Lifson <farrel.lifson@gmail.com> wrote:
> Is it possible to mix in a module method to become a class method? I'd
> like to define the method_added method in a module and then mix it
> into a class like so
> module Foo
> def self.method_added(method)
> puts "Added #{method}"
> end
> end
>
> class Bar
> include Foo
> def bar
> end
> def baz
> end
> end
> So that I get
> Added bar
> Added baz
> printed out. Is there any way to do this besides making Foo a class
> and subclassing Foo from it?
>
> Farrel

See previous thread: 'Ruby for Rails p.462-464 - why include vs.
extend?' or api.rubyon rails and there *::*::ClassMethods

basicly something like this:

module A
module M
module ClassMethods
def some_method
#...
end

def included(c)
c.extend(ClassMethods)
end
end
end

and then a class later that does this:

class B
include A::M
end

Gavin Kistner

10/18/2006 1:39:00 PM

0

Farrel Lifson wrote:
> Is it possible to mix in a module method to become a class method? I'd
> like to define the method_added method in a module and then mix it
> into a class like so
[...snip...]
> So that I get
> Added bar
> Added baz
> printed out.

module Foo
def method_added(method)
puts "Added #{method}"
end
end
class Bar
extend Foo
def bar; end
def baz; end
end

Gavin Kistner

10/18/2006 1:56:00 PM

0

Jan Svitok wrote:
> module A
> module M
> module ClassMethods
> def some_method
> #...
> end
>
> def included(c)
> c.extend(ClassMethods)
> end
> end
> end

The extra ClassMethods module is needed because self methods of a
module are never mixed into the lookup flow. See note #3 at
http://phrogz.net/RubyLibs/RubyMethodLook... - using 'extend'
instead of 'include' causes the left end of the mixed-in module line to
come from the 'class methods' side of the extended class, but doesn't
change that the right end always points to the 'instance' methods of
the module.

(Right?)

Trans

10/18/2006 2:47:00 PM

0


Farrel Lifson wrote:
> Is it possible to mix in a module method to become a class method? I'd
> like to define the method_added method in a module and then mix it
> into a class like so
> module Foo
> def self.method_added(method)
> puts "Added #{method}"
> end
> end
>
> class Bar
> include Foo
> def bar
> end
> def baz
> end
> end
> So that I get
> Added bar
> Added baz
> printed out. Is there any way to do this besides making Foo a class
> and subclassing Foo from it?

Search ruby-talk for #class_extension.

require 'facet/module/calss_extension'

module Foo
class_extension {
def method_added(method)
puts "Added #{method}"
end
}
end

T.

Ara.T.Howard

10/18/2006 3:14:00 PM

0

Verno Miller

10/18/2006 3:44:00 PM

0

> Posted by Farrel Lifson (Guest)
> on 18.10.2006 15:05
>
> Is it possible to mix in a module method to become a class method?


Yet another approach:

http://redcorundum.blogspot.com/2006/06/mixing-in-class-me...

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

Rick DeNatale

10/19/2006 12:42:00 AM

0

On 10/18/06, ara.t.howard@noaa.gov <ara.t.howard@noaa.gov> wrote:
> On Wed, 18 Oct 2006, Farrel Lifson wrote:
>
> > Is it possible to mix in a module method to become a class method? I'd
> > like to define the method_added method in a module and then mix it
> > into a class like so
> > module Foo
> > def self.method_added(method)
> > puts "Added #{method}"
> > end
> > end
> >
> > class Bar
> > include Foo
> > def bar
> > end
> > def baz
> > end
> > end
> > So that I get
> > Added bar
> > Added baz
> > printed out. Is there any way to do this besides making Foo a class
> > and subclassing Foo from it?
> >
> > Farrel
>
> harp:~ > cat a.rb
> module Foo
> #def self.method_added(method)
> def method_added(method)
> puts "Added #{method}"
> end
> end
>
> class Bar
> #include Foo
> extend Foo
> def bar
> end
> def baz
> end
> end
>
> harp:~ > ruby a.rb
> Added bar
> Added baz
>
>
> if you need both instance and class methods to be in Foo, then you'll want:
>
>
> harp:~ > cat a.rb
> module Foo
> #def self.method_added(method)
> module ClassMethods
> def method_added(method)
> puts "Added #{method}"
> end
> end
> module InstanceMethods
> def foo() 42 end
> end
> def self.included other
> other.module_eval{
> extend ClassMethods
> include InstanceMethods
> }
> end
> end
>
> class Bar
> include Foo
> def bar
> end
> def baz
> end
> end
>
> p Bar.new.foo
>
>
> harp:~ > ruby a.rb
> Added bar
> Added baz
> 42
>
>
> -a
> --
> my religion is very simple. my religion is kindness. -- the dalai lama

No need for the separate module for instance methods;

rick@frodo:/public/rubyscripts$ cat a1.rb
module Foo

module ClassMethods
def method_added(method)
puts "Added #{method}"
end
end

def self.included(other)
other.extend ClassMethods
end

def foo
42
end
end

class Bar
include Foo

def bar
end

def baz
end
end

p Bar.new.foo
rick@frodo:/public/rubyscripts$ ruby a1.rb
Added bar
Added baz
42


--
Rick DeNatale

My blog on Ruby
http://talklikeaduck.denh...

Ara.T.Howard

10/19/2006 5:00:00 AM

0

Trans

10/19/2006 12:06:00 PM

0


Verno Miller wrote:
> > Posted by Farrel Lifson (Guest)
> > on 18.10.2006 15:05
> >
> > Is it possible to mix in a module method to become a class method?
>
>
> Yet another approach:
>
> http://redcorundum.blogspot.com/2006/06/mixing-in-class-me...

This looks like much like #class_extension. How does this differ?

An interesting side note to this. I recetnly ran into the opposite case
wehere I wanted to prevent a class method (of a class) from being
inherited by the subclass. I had to use some method programming tricks
to undef the particular method. This further leads me to believe that
the best solution is to allow deignation of methods as inheritable or
not in much the same way we designate private/public. Classes' class
methods would be inheritable be default, module's not. This could also
be used for instance methods to create namespace local methods.

T.