From: Keith Rarick <kr@...>
Date: 2007-08-04T07:24:28+09:00
Subject: Re: method_added hook and class methods

Nobuyoshi Nakada wrote:
> Hi,
> 
> At Fri, 3 Aug 2007 15:29:06 +0900,
> Keith Rarick wrote in [ruby-talk:263159]:
>> Now I want to observe when class methods are defined. My understanding
>> of ruby says that "class methods" are really just instance methods of
>> the metaclass. So I do this:
>> 
>> class C
>>   class << self
>       def singleton_method_added(name)
>         puts 'added ' + name.to_s
>       end

Thanks very much! This works perfectly.

Out of curiosity, why are metaclasses treated differently than regular 
classes in this respect?

Suppose I am given a variable, x, that contains a class. The object may 
be either a class or a metaclass, and I wish to observe the creation of 
instance methods on x. Now I must do one of two different things 
depending on the type of x (class or metaclass). (For the sake of 
brevity, I assume a metaclass() method and ignore the fact that 
define_method() is private.)

If x is a regular class:

x.metaclass.define_method(:method_added) { |name| puts "added #{name}" }

or, if x is a metaclass:

x.define_method(:singleton_method_added) { |name| puts "added #{name}" }

Further, I do not know of a reliable way to determine if x is a regular 
class or a metaclass, so I must actually do *both* if I want to be sure 
to see the addition of a method on x.

Is this an accurate description or am I missing something?

kr
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