From: Gioele Barabucci <ml@...>
Date: 2006-01-22T07:28:28+09:00
Subject: class methods like attr:

How can I create methods like "attr:" that can create methods and instance 
variables?

I'd like to do this

  class B < A
    my_property :k, "K"
    def test
      p @k # should print "K"
      p @@my_properties # should print ['k']
    end
  end

I tried with this (non-) solution

  class A
    def A.my_property(sym, val)
      self.instance_eval {
        @@my_properties ||= Array.new()
        @@my_properties << sym.to_s
        eval "@#{sym.id2name} = \"#{val}\""
        # p @k1 # << this shows "K1.B" or "K1.C" as expected
      }
    end
  end

but these tests showed me that I was wrong

  class A
    def test
      p @@my_properties
    end
  end

  class B < A
    my_property :k1, "K1.B" # k1 is a string fixed to "K1"
    my_property :k2, "K2.B"
    def test
      super  # should be ['k1', 'k2']
      p @k1  # should be "K1"
    end
  end
  
  class C < A
    my_property :k1, "K1.C"
    def test
      super  # should be ['k1']
      p @k1  # should be "K1.C"
    end
  end

A.new.test (should print nil or a warning) => ["k1", "k2", "k1"]

B.new.test (should print ['k1', 'k2'] 'K1.B') => ["k1", "k2", "k1"]
./at.rb:28: warning: instance variable @k1 not initialized
nil

A.new.test (should print nil or a warning) => ["k1", "k2", "k1"]

C.new.test (should print ['k1'] 'K1.C') => ["k1", "k2", "k1"]
./at.rb:36: warning: instance variable @k1 not initialized
nil

Any suggestion or idea?

--
Gioele <dev@gioelebarabucci.com>