From: Louis J Scoras <louis.j.scoras@...>
Date: 2005-10-04T05:40:51+09:00
Subject: [Solution]: Lisp partial solution - meta-programming help

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Hi all;

I started to give the lisp quiz a go. From the begining, I resolved to try
for a solution such that the map can be set up in a declarative manner.

I wanted it to look something like the attr_ class methods and ActiveRecord=
s
`associations`; however, setting up something like this seems to be more
work than I thought it would be. Following is some working code, but it's
pretty ugly. Setting the class variable in this manner just feels very
hackish, yet it's the only way I could seem to get this to work.

The problem was this: how to write the methods so that they don't have to b=
e
explicitly overwritten in the subclasses, and yet they can reference these
concrete classes state?

Anyone with a bit more ruby experiance have any refactoring ideas?


--
Lou


module LocationClassMethods
def exit_to(place,direction,opts=3Dnil)
portal =3D (opts[:through] || opts[:via] if opts.respond_to?:[]) || 'door'
class_variable_set(:@@exits, []) unless class_variables.include?(:@@
exits.to_s)
exits =3D class_variable_get(:@@exits)
exits << Exit.new(direction,portal)
end

def description(desc)
class_variable_set(:@@description, desc)
end

def exits
class_variable_get(:@@exits)
end

def get_description
class_variable_get(:@@description)
end

end

class Location
def self.inherited(sub)
sub.extend(LocationClassMethods)
end

def initialize
@exits =3D self.class.exits
@description =3D self.class.get_description
end

def describe
puts @description
describe_exits
end

def describe_exits
@exits.each { |e| puts e.describe }
end
end

class Attic < Location
exit_to :living_room, :down, :via =3D> 'staircase'

description 'You are in the attic of the wizard\'s house. There is a giant
welding torch in the corner.'
end

class Garden < Location
exit_to :living_room, :west

description 'You are standing in a beautiful garden. There is a well in
front of you.'
end

class LivingRoom < Location
exit_to :attic, :up, :via =3D> 'staircase'
exit_to :garden, :east

description 'You are in the living-room of a wizard\'s house. There is a
wizard snoring loudly on the couch.'
end


a =3D Attic.new
a.describe

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