From: "David A. Black" <dblack@...>
Date: 2005-08-13T02:17:14+09:00
Subject: Re: eval, attr_* like methods

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Hi --

On Sat, 13 Aug 2005, [ISO-8859-1] Brian Schr=F6der wrote:

> On 12/08/05, Patrick Gundlach <clr7.10.randomuser@spamgourmet.com> wrote:
>> Dear all,
>>
>> I'd like to create methods similar to the attr_* way. I'd like to
>> write
>>
>> class Foo
>>   lookup_meth :bar, :baz
>>
>>   def some_other_methods
>>       ....
>>   end
>>
>> end
>>
>> The lookup_meth should define for class Foo methods such as
>>
>> def bar
>>   # tricky lookup stuff
>>   return value
>> end
>> def bar=3D(obj)
>>   @bar=3Dobj
>> end
>>
>>
>> How would I write such lookup_meth? I've been playing a bit with eval,
>> but I didn't get it quite right.
>>
>> Patrick
>>
>>
>
> class Object
>  def self.lookup_meth(*args)
>    args.each do | name |
>      eval %(
>      def #{name}
> =09@#{name} ||=3D '24'
>      end
>
>      def #{name}=3D(arg)
> =09@#{name} =3D arg
>      end
>      )
>    end
>  end
> end
>
> class Test
>  lookup_meth :test1, :test2
>
>  def testme
>    p self.test1
>    self.test1 =3D 42
>    p self.test1
>  end
> end
>
> Test.new.testme
> =3D>
> "24"
> 42

# However.....

   p test1   =3D> "24"

You've defined them as instance methods of Object, so they appear at
the top level.

You'd probably want:

   class Module
     def lookup_meth(*args)
       args.each do |arg|
         define_method(arg) do
           instance_variable_get("@#{arg}")
         end
         define_method("#{arg}=3D") do |v|
           instance_variable_set("@#{arg}", v)
         end
       end
     end
   end

or similar.


David

--=20
David A. Black
dblack@wobblini.net
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