From: Greg Millam <ruby-talk@...>
Date: 2006-02-20T04:55:30+09:00
Subject: Re: [SOLUTION] metakoans.rb (#67)

Here's my solution: Took me about 15 minutes to solve the koans. I agree 
with everyone else: Great quiz =). Continuous fiddling with it made me 
late for a date, and when I tried explaining why, she just stared at me. 
"Meta cones? What's that?" Ah well!

My koan solution, 9 lines:

def one_attribute(arg,&b)
   name = (arg.is_a?(Hash) ? arg.keys[0] : arg).to_s
   p    = Hash.new( arg.is_a?(Hash) ?  arg[name] :  nil  )
   fun  = lambda { |*args|
     p[self] = *args unless args.empty?
     (p.include?(self) or !b) ? p[self] : instance_eval(&b)
   }
   ['','?','='].each { |ch| define_method(name+ch,&fun) }
end

And to make it accept multiple arguments to work with the benchmark 
suites (10 lines):

def attribute(arg,&b)
   attribute(*rest,&b) if rest.any?
   name = (arg.is_a?(Hash) ? arg.keys[0] : arg).to_s
   p    = Hash.new( arg.is_a?(Hash) ?  arg[name] :  nil  )
   fun  = lambda { |*args|
     p[self] = *args unless args.empty?
     (p.include?(self) or !b) ? p[self] : instance_eval(&b)
   }
   ['','?','='].each { |ch| define_method(name+ch,&fun) }
end

With comments:

def attribute(arg,&b)
   # Allow multiple attributes to be set and defined.
   attribute(*rest,&b) if rest.any?

   # The name of the attribute.
   name = (arg.is_a?(Hash) ? arg.keys[0] : arg).to_s

   # p holds all the attributes for each object.
   # This is wasteful since in real use, this would cause
   # Each object that's set an attribute to be kept in
   # memory.
   p    = Hash.new( arg.is_a?(Hash) ?  arg[name] :  nil  )

   # The only method I define: It takes 1 or more arguments.
   # If it's given an argument, it assigns. In all cases,
   # It returns.
   fun  = lambda { |*args|
     # Assign if necessary.
     p[self] = *args unless args.empty?
     # If it's been assigned, or there's no block, return
     # Its saved value (Or Hash's default)
     (p.include?(self) or !b) ? p[self] : instance_eval(&b)
   }

   # Assign that method to all 3 methods we need.
   ['','?','='].each { |ch| define_method(name+ch,&fun) }
end


More quizzes like this would be much appreciated. It rocked.

Ara++

- Greg