From: ts <decoux@...>
Date: 2002-11-20T23:36:53+09:00
Subject: Re: Need help dynamically creating classes.

>>>>> "P" == Paul Gregory <pgregory@aqsis.com> writes:

P> Next question: is it possible to specify arguments to the initialize
P> method when defining it with this code?

 Well, you can write

pigeon% cat b.rb
#!./ruby

class SceneObject
   def initialize(scale, &generate)
      @scale = scale
      @generate = generate
   end
   alias init initialize

   def render
      instance_eval(&@generate)
   end
end

def defineClass(name, &block)
   Object.const_set(name, Class.new(SceneObject)).instance_eval do
      define_method(:initialize) {|scale| init(scale, &block) }
   end
end

defineClass("MyObject") do
   puts "render some object #{self.inspect}"
end

a = MyObject.new(1.5)
a.render
pigeon%
 
pigeon% b.rb
render some object #<MyObject:0x401abc2c @generate=#<Proc:0x401abd30@./b.rb:21>, @scale=1.5>
pigeon% 

P> I'd like to be able to do something like...

P> defineClass("MyObject", scale) {
P>     scale(scale)
P>     puts(scale)
P> }

 but in this case you must write it

   defineClass("MyObject") {
      scale(@scale)
      puts(@scale)
   }

 Or you can make someting more complex

pigeon% cat b.rb
#!./ruby

class SceneObject
   def initialize(params, &generate)
      params.each do |k, v|
         class << self; self end.send(:attr_accessor, k)
         send("#{k}=", v)
      end
      @generate = generate
   end
   alias init initialize

   def render
      instance_eval(&@generate)
   end
end

def defineClass(name, var, &block)
   Object.const_set(name, Class.new(SceneObject)).instance_eval do
      define_method(:initialize) {|scale| init(var => scale, &block) }
   end
end

defineClass("MyObject", "scale") do
   puts "render some object #{self.inspect}"
   p self.scale
end

a = MyObject.new(1.5)
a.render
pigeon% 

pigeon% b.rb
render some object #<MyObject:0x401ab7e0 @scale=1.5, @generate=#<Proc:0x401ab8f8@./b.rb:24>>
1.5
pigeon% 

 but you must prefix `scale' with `self.' otherwise ruby interpret it as a
 local variable.


Guy Decoux