From: ptkwt@...1.aracnet.com (Phil Tomson)
Date: 2002-03-14T17:05:51+09:00
Subject: Re: Method type 'abstract' (Module#abstract)

In article <3C9009A9.FC285892@stud.ntnu.no>,
Kent Dahl  <kentda@stud.ntnu.no> wrote:
>Phil Tomson wrote:
>> class MyClass
>>   abstract :some_method
>> end
>> 
>> mc = MyClass.new
>
>Ugh! Some Java/C++ idiom just reared its head in the back of my skull
>when seeing this. Since MyClass is abstract, I would expect the call to
>new to freak too. (Fail early) 

Perhaps, but you could redefine it later (classes are always open) or add 
it as a singleton method so I'm not sure you would want new to fail right 
away.

Actually, I think it's kind of cool that though Ruby doesn't have the 
concept of abstract methods built-in, you can easily mimick them with less 
than 10 lines of code.

>
>Which reminds me: Is there any way of seeing which methods have been
>redefined between a super- and subclass?
>
>SubClass.instance_methods - SuperClass.instance_methods return the new
>methods, but how could I get a list of methods that SubClass has
>redefined, if that is possible?
>

Wouldn't you just get the list of SubClass methods that also exist 
in the SuperClass?  Something like (I'm sure there is an easier/more 
efficient way):

redefinedMethods = []
superClassMethods = SuperClass.instance_methods
SubClass.instance_methods.each { |subMethod|
   if superClassMethods.include?(subMethod)
      redefinedMethods << subMethod
   end
end

Actually, come to think of it couldn't you just 'and' the two arrays?

redefinedMethods = SuperClass.instance_methods & SubClass.instance_methods

Phil