From: Pit Capitain <pit@...>
Date: 2005-12-27T17:25:51+09:00
Subject: Re: can't figure out what's wrong

Erik, there are some typos in your code. See below.

erik blas schrieb:
> I'm reading the why's ruby guide, and i've retyped a class in the guide 
> to use through the metaprogramming chapter. when i try to use it with 
> irb i get this error:
> nomethoderror: undefined method '[]=] for nil:class
>  from path/dwemthy.rb:18:in 'life'

This means that in line 18, you tried to call method "[]=" on nil. Nil 
doesn't have such a method, so the NoMethodError is raised.

>  from path/dwemthy.rb:16:in 'life'
>  from path/rabbit.rb:4
> 
> here's the code for dwemthy.rb:
> class Creature
> 
> 	# get a metaclass for this class
> 	def self.metaclass; class << self; self; end; end
> 
> 	# advanced metaprogramming cord for clean traits
> 	def self.traits( *arr )
> 		return @traits if arr.empty?
> 
> 		# 1. setup accessors for each variable
> 		attr_accessor *arr
> 
> 		# 2. add a new class method to each trait
> 		arr.each do |a|
> 			metaclass.instance_eval do
> 				define_method( a ) do |val|
> 					@triats ||= {}
> 					@traits[a] = val

This is line 18. It looks like an assignment, but it really is a method 
call. It calls method "[]=" on the object @traits with arguments a and 
val. The error message above means that @traits is nil. If you look at 
the previous line (line 17), you notice the typo.

> 				end
> 			end
> 		end
> 
> 		# 3. for each monster, the 'initialize' method should use
> 		#     the default number for each trait
> 		class_eval do
> 			define_method( :initialize ) do
> 				self.class.traits.each do |k,v|
> 					instance_varable_set("@#{k}", v)

This should be "instance_variable_set". Note the missing "i".

> 				end
> 			end
> 		end
> 	end

I haven't looked further. HTH.

Regards,
Pit