From: Robert Klemme <shortcutter@...>
Date: 2008-04-01T17:42:25+09:00
Subject: Re: MetaMonster

2008/3/31, Ruhe <nocturneer@gmail.com>:
> Hi.
>  I needed something like a Vector class,
>  but with named elements, and default params in constructor.
>  I needed to add, subtract, multiply my own vectors.

That instantly reminds of Struct.

>  At the same time a learned a lot about metaprogramming.
>  So I decided to make my own monster :)
>  http://pastie.caboo.se/173413
>
>  I don't hope that my work is useful in real-world app,
>  but I would like to see critics of my metaprogramed monster.
>  What is wrong, what could be done better.
>
>  PS
>  I understand that this is a bad way to build class,
>  I did it to get new skills in metaprogramming, not for real-world use.

Here are my 0.02EUR:

Make create and others class instance methods instead of instance
methods.  You do not need the instance for anything else than creating
classes so it's obsolete.  At least it should not be visible from the
outside.

You could save some typing by integrating this with Struct, i.e. let
Struct do all that it does already and only add mathematic methods,
like

class Vector
  def self.new(*syms)
    cl = Struct.new(*syms)
    # add math instance methods to cl
    cl
  end
end

I'd probably also generate the method code and class_eval it vs. using
instance_variable_set and *get because that code is likely faster and
you do not need a closure, e.g.

    %w{+ -}.each do |op|
      cl.class_eval = %Q{
        def #{op}(other)
          self.class.new(#{syms.map {|s| "self.#{s} #{op}
other.#{s}"}.join(', ')})
        end
      }
    end

Ah, and why the many empty lines?  Or is this just a pasting artifact?

Kind regards

robert

-- 
use.inject do |as, often| as.you_can - without end