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List:       ruby-talk
Subject:    Re: class methods like attr:
From:       Wilson Bilkovich <wilsonb () gmail ! com>
Date:       2006-01-23 15:23:55
Message-ID: d4e4955b0601230651m612b9e88j5f36ad06016dce3 () mail ! gmail ! com
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Check this tutorial/game/artwork out:
http://poignantguide.net/dwemthy/

By the end, you will definitely know how to create methods that behave
like attr_accessor.

On 1/21/06, Gioele Barabucci <ml@gioelebarabucci.com> wrote:
> 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>
>
>


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