From: laotse@...
Date: 2001-06-29T04:56:01+09:00
Subject: [ruby-talk:17028] Wrapping Methods


Hello all. I'm still playing around with dynamically mapping methods and
ran into a problem I'm trying to work out. I have two versions of a
script. One has everything contained in a class file, and works. One has
part of the method definitions in a mixin that is included, and it does
not work. Here's the code:

-- [ CODE THAT WORKS ] --------------------------------------------
class Redef
	def set_watchpoint(method)
		original_method = method + "_orig"
		unless defined? self.original_method
			self.type.class_eval {
				alias_method original_method, method
			}
		end
		eval <<-ENDEVAL
			def #{method}(*args)
				result = #{original_method}(*args)
				print "success\n"
				result
			end
		ENDEVAL
	end
	def hello
		print "hello\n"
	end
end

test = Redef.new
test.hello
test.set_watchpoint("hello")
test.hello
------------------
this outputs:

hello
hello
success

--[ CODE THAT DOES NOT WORK ]-------------------------------------------
module Redef
	def set_watchpoint(method)
		original_method = method + "_orig"
		unless defined? self.original_method
			self.type.class_eval {
				alias_method original_method, method
			}
		end
		eval <<-ENDEVAL
			def #{method}(*args)
				result = #{original_method}(*args)
				print "success\n"
				result
			end
		ENDEVAL
	end
end

class Hello
	include Redef
	def hello
		print "hello\n"
	end
end


test = Hello.new
test.hello
test.set_watchpoint("hello")
test.hello
-------------------
this outputs:

hello
hello

-----------------------------------------------------------------------------

Sorry for all the questions :) Still struggling to come up to speed on
Ruby. If along with a suggested fix, if anyone could suggest what portions
of the book (or online docs) I can read to understand why my first code
works and my second doesn't, that would be great.

-----------------------------------------------------------------------------
Brian Knox
Just Another Perl Hacker
perl -le '$_="6110>374086;2064208213:90<307;55";tr[0->][ LEOR!AUBGNSTY];print'