Sending extend and include to your own class definition


#1

hello.

I’m trying to learn the ruby way of doing things, and ran across some
code that I’m finding hard to understand. It seems to be sending
extend and include messages of inner modules to the class def itself.

I’ve boiled the sample down to something like this.

class C

module ClassMethods
def c1
‘Class method c1’
end

def c2
  'Class method c2'
end

end

send :extend, ClassMethods

module InstanceMethods
def i1
‘Instance method i1’
end

def i2
  'Instance method i2'
end

end

send :include, InstanceMethods

end


I think I must be missing something.

Isn’t the receiver of the send message the Class itself? If not, who
is the receiver?

If it is, what does this technique offer compared to just declaring
the class and instance methods in the first place?

I’d really appreciate some clarification about this style.

TIA.


#2

On May 22, 2009, at 3:40 PM, rlf wrote:

I’m trying to learn the ruby way of doing things, and ran across some
code that I’m finding hard to understand. It seems to be sending
extend and include messages of inner modules to the class def itself.

send :extend, ClassMethods
[…]
send :include, InstanceMethods

These could be more simply written as:
extend ClassMethods
include InstanceMethods

Isn’t the receiver of the send message the Class itself? If not, who
is the receiver?

Yes, the class ‘C’ is the receiver.

If it is, what does this technique offer compared to just declaring
the class and instance methods in the first place?

Perhaps because the modules are going to be used elsewhere? If you
declare the methods directly as class and instance methods it is
awkward to incorporate them into other classes or modules via extend
and include.