Dynamically creating class methods

Ruby
1

I want to create a class method which allows us to create further class
methods, so something like:

class Test
class << self
def create_method(name, proc)
self.class.send(:define_method, name, proc)
end
end
end

proc = lambda {puts ‘Hello world’}
Test.create_method(:foo, proc)
Test.foo #want this
Integer.foo #don’t want this

The problem with the above is that create_method adds foo to all
classes. self.send on its own doesn’t seem to do what I want - it adds
foo as instance method instead.

The method will eventually be placed in an module to be mixed in when
desired, although I don’t think that matters here.

Ideas?

2

Hi –

On Wed, 1 Jul 2009, Shak Shak wrote:

proc = lambda {puts ‘Hello world’}
Test.create_method(:foo, proc)
Test.foo #want this
Integer.foo #don’t want this

The problem with the above is that create_method adds foo to all
classes. self.send on its own doesn’t seem to do what I want - it adds
foo as instance method instead.

There are three candidates for the class to which you might send the
:define_method message:

  1. Test
  2. Class
  3. the singleton class of Test

#3 is the one you want. The code you’ve written sends the message to
Class, and the self.send that you’ve tried sends it to Test.

Try this:

class Test
def self.create_method(name, proc)
s_class = class << self; self; end
s_class.send(:define_method, name, proc)
end
end

There are other ways (including using class_eval), but that’s the
general idea.

David