From: ts <decoux@...>
Date: 2001-09-03T21:36:48+09:00
Subject: [ruby-talk:20769] Re: Dynamic generation of class variables?

>>>>> "R" == Renald Buter <buter@CWTS.LeidenUniv.nl> writes:

R> NEXT to that, I would like to enter 'max' and 'min' as keys into a class
R> variable '@@properties' to allow me to inspect which properties a
R> particular instance has. 

 use the class variable @properties

 If I take your example in [ruby-talk:20614] this give something like this

pigeon% cat b.rb
#!/usr/bin/ruby
class A
   def self.property( token, value )
      unless respond_to?(:properties)
         @properties = {}
         class_eval <<-EOD
         def self.properties
            @properties
         end
         EOD
      end
      @properties[token.to_s] = value
      class_eval <<-EOD
      def #{token}
         @#{token} ? @#{token} :
                     @#{token} = self.class.properties["#{token}"]
      end
      def #{token}=( value )
         @#{token} = value
      end
      EOD
   end
end

class B < A
   property :a, [1, 2]
   property :b, "foo"
end

class C < A
   property :c, 10
end

### Testing ###

b1 = B.new
b2 = B.new
b1.b = 2
c = C.new

p B.properties
B.properties.each do |p, h| 
   puts "original value #{h} b1=#{b1.method(p).call},b2=#{b2.method(p).call}"
end
p C.properties

puts c.c
pigeon% 
 
pigeon% b.rb
{"a"=>[1, 2], "b"=>"foo"}
original value 12 b1=12,b2=12
original value foo b1=2,b2=foo
{"c"=>10}
10
pigeon% 



Guy Decoux