Can't figure out what's wrong


#1

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’
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
			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)
			end
		end
	end

end

# creature attributes are read only
traits :life, :strength, :charisma, :weapon

# this method applies a hit taken during a fight
def hit( damage )
	p_up = rand( charisma )
	if p_up % 9 == 7
		@life += p_up / 4
		puts "[#{ self.class } magick powers up #{ p_up }!]"
	end

	# this method takes one turn in a fight
	def fight( enemy, weapon )
		if life <= 0
			puts "[#{ self.class } is too dead to fight!]"
			return
		end

		# attack opponent
		your_hit = rand( strength + weapon )
		puts "[You hit with #{ your_hit } points of damage!]"
		enemy.hit( your_hit )

		# retaliation
		p enemy
		if enemy.life > 0
			enemy_hit = rand( eneme.strenght + enemy.weapon )
			puts "[Your enemy hit with #{ enemy_hit } points \
			of damage!] "
			self.hit( enemy_hit )
		end
	end

end

end

class DwemthysArray < Array
alias _inspect inspect
def inspect; “#<#{ self.class }#{ _inspect }>”; end
def method_missing( meth, *args )
answer = first.send( meth, *args )
if first.life <= 0
shift
if empty?
puts “[Whoa. You decimated Dwemty’s Array!]”
else
puts “[Get ready. #{ first.class } has emerged.]”
end
end
answer || 0
end
end


#2

here is the code for rabbit.rb:
class Rabbit < Creature
traits :bobs

life 10
strength 2
charisma 44
weapon 4
bombs 3

# little boomerang
def ^( enemy )
	fight( enemy, 13 )
end

# the hero's sword is unlimited
def /( enemy )
	fight( enemy, rand( 4+ ( ( enemy.life % 10 ) ** 2 ) ) )
end

# lettuce will build your strength and extra ruffage
# will fly in the face of your opponent
def %( enemy )
	lettuce = rand( chairsma )
	puts "[Healthy lettuce gives you#( lettuce ) life points!!]"
	@life += lettuce
	fight( enemy, 0 )
end

# bombs, but you have only threee
def *( enemy )
	if @bombs.zero?
		puts '[Out of bombs!]'
		return
	end
	@bombs -= 1
	fight( enemy, 86 )
end

end


#3

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.

def self.traits( *arr )
@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


#4

Thank you for the help. Guess I’m just tired and didn’t notice all the
typos. Was driving me up the wall.


#5

On Tue, 27 Dec 2005 18:52:23 +0900, erik blas removed_email_address@domain.invalid
wrote:

Thank you for the help. Guess I’m just tired and didn’t notice all the
typos. Was driving me up the wall.

When typing in a program that has been provided, typos in Ruby can be
irritating, as you’ve seen.

When building my own programs, I try to go in smaller bites in Ruby than
I might
in C# or Java, because syntax errors and typos are often hard to find.