From: Rune Hammersland <rune@...>
Date: 2006-10-31T20:37:17+09:00
Subject: Difference between define_method and def method; end

Hello dear Rubyists.

It was suggested on the IRC channel that I try the ML for this  
problem ...

While looking at how to undefine a method, I found out that there is  
a difference in how define_method and the def ... end block works.  
Example coming up:

# Two classes to play with.
class Parent
     def lol
         puts "P: LOL"
     end
end

class Child < Parent
     # Commenting out the redefinition doesn't help
     def lol
         puts "C: LOL"
     end
end

# test1.rb
c = Child.new
c.lol # => "C: LOL" or "P: LOL" if commented out
Child.class_eval { undef_method :lol }

# Try to redefine method and call super.
class Child < Parent
     def lol
         print "LOL: "
         begin
             super
         rescue NameError => e
             puts e.to_s
         end
     end
end

c.lol # => "LOL: superclass method `lol' disabled"

# Then in test2.rb:

c = Child.new
c.lol # => "C: LOL", or "P: LOL" if commented out.

Child.class_eval { undef_method :lol }
# Try to redefine method and call super.
Child.class_eval do
     define_method(:lol) { print "LOL: "; super }
end
c.lol # => "LOL: P: LOL"

Now ... Why can I call super in the redefinition of the method using  
define_method, and not using the def ... end block? For me this seems  
like an inconsistency. First I thought it was neat that I could not  
call super in the method after using undef_method and redefining it  
again, but then I found out I could using define_method.

As the comments state, I also tried to run the code with the  
redefinition of the lol method in the Child class, but to no help.  
The output is roughly the same (P instead of C obviously).

Anybody care to shed a little light on this?

-- 
Vennlig Hilsen
Rune Hammersland