Forum: Ruby dynamically define attr_accessors on objects?

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Aaron S. (Guest)
on 2007-06-25 20:23
How can I dynamically define attr_accessors on an object?

EX:;:
class Person
  attr_accessor :firstname
end
p = Person.new
p.firstname = 'aaron'
p.instance_variable_set(:@lastname, 'smith')
puts p.inspect
puts p.firstname
puts p.lastname

the last line generates an "undefined method lastname" error..

any ideas?
thanks
MenTaLguY (Guest)
on 2007-06-25 20:31
(Received via mailing list)
On Tue, 26 Jun 2007 01:23:44 +0900, Aaron S.
<removed_email_address@domain.invalid> wrote:
> How can I dynamically define attr_accessors on an object?
>
> EX:;:
> class Person
>   attr_accessor :firstname
> end
> p = Person.new
> p.firstname = 'aaron'

class << p
  attr_accessor :lastname
end
p.lastname = 'smith'

> puts p.inspect
> puts p.firstname
> puts p.lastname

You have to explicitly create the accessor methods; you don't get them
automatically when setting an instance variable.

-mental
Robert K. (Guest)
on 2007-06-25 21:31
(Received via mailing list)
On 25.06.2007 18:23, Aaron S. wrote:
> puts p.firstname
> puts p.lastname
>
> the last line generates an "undefined method lastname" error..
>
> any ideas?

Use OpenStruct.

  robert
Phil T. (Guest)
on 2007-06-26 04:54
(Received via mailing list)
On 6/25/07, Aaron S. <removed_email_address@domain.invalid> wrote:
> puts p.firstname
> puts p.lastname
>
> the last line generates an "undefined method lastname" error..
>
> any ideas?
> thanks
>
> --

I suppose you could do something like:

  class Person
   def def_accessor name, val=nil
     self.class.class_eval { attr_accessor name.intern }
     instance_variable_set ( "@#{name}".intern, val )
   end
 end

Then you could do something like:
h = { "fooname"=>"Foo", "age"=>28 }
h.each {|key,value|  p.def_accessor key, value }


...but the other suggestion to use OpenStruct is probably a better idea.

Phil
Aaron S. (Guest)
on 2007-06-26 07:32
thanks for the suggestions.. went with the openstruct.
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