Mixin a module method as a class method

Ruby
1

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

2

On 10/18/06, Farrel L. [email protected] wrote:

include Foo

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

3

Farrel L. 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

4

Farrel L. wrote:

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.

5

Jan S. wrote:

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/RubyMethodLookupFlow.png - 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?)

6

Posted by Farrel L. (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-methods.html

7

On Wed, 18 Oct 2006, Farrel L. wrote:

include Foo

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

8

On 10/18/06, [email protected] [email protected] wrote:

printed out. Is there any way to do this besides making Foo a class
end
harp:~ > ruby a.rb
module ClassMethods
include InstanceMethods
end
-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.denhaven2.com/

9

Verno Miller wrote:

Posted by Farrel L. (Guest)
on 18.10.2006 15:05

Is it possible to mix in a module method to become a class method?

Yet another approach:

Ruby, iOS, and Other Development: Mixing in Class Methods

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.

10

On Thu, 19 Oct 2006, Rick DeNatale wrote:

No need for the separate module for instance methods;

no. you are correct, it’s just a convention which signifies to the
uninitiated what is happening.

regards.

-a