From: Eero Saynatkari <ruby-ml@...>
Date: 2006-10-24T01:38:33+09:00
Subject: Re: newbie: class attribute accessors?

--J+xDcZ1j08+V/OfU
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
Content-Transfer-Encoding: quoted-printable

On 2006.10.23 20:25, John Turner wrote:
> Diego Virasoro wrote:
> >>Please explain. Use an example.
> >
> >>From what I understood, for any instance variable, I can make ruby
> >automatically produce the accessors. For example:
> >
> >class Dog
> >   @name
> >   @@NumberOfLegs =3D 4
> >
> >   attr_accessor :name
> >end
> >
> >x =3D Animal.new
> >...
> >puts x.name
> >
> >
> >However, I would like to do something similar for class variables. So
> >for example in the above example, for @@NumberOfLegs.
> >
> >Is this possible?
> >
> >Thank you
> >
> >Diego Virasoro
> >
>=20
> You can do this for instance variables of a class, not sure there are=20
> equivalents for actual class variables though:
>=20
> class Dog
>   @names =3D ["Fido", "Rex"]
>   class << self
>      attr_accessor :names
>   end
> end
> puts Dog.names

Please note that it is often better to use class instance variables
(@var at the class scope) rather than class variables (@@var):

 class A;     @@a =3D 5; end
 class B < A; @@a =3D 4; end
 class C < A; @@a =3D 3; end
 class D < B; @@a =3D 2; end

 p A.send 'class_variable_get', "@@a"
 p B.send 'class_variable_get', "@@a"
 p C.send 'class_variable_get', "@@a"
 p D.send 'class_variable_get', "@@a"

 class C; @@a =3D 4; end

 p A.send 'class_variable_get', "@@a"
 p B.send 'class_variable_get', "@@a"
 p C.send 'class_variable_get', "@@a"
 p D.send 'class_variable_get', "@@a"

Class instance variables have a simpler inheritance, none:

 class E; @a =3D 1; end
 class F < E; end

 p E.send 'instance_variable_get', '@a'
 p F.send 'instance_variable_get', '@a'

 class F; @a =3D 2; end

 p E.send 'instance_variable_get', '@a'
 p F.send 'instance_variable_get', '@a'

--J+xDcZ1j08+V/OfU
Content-Type: application/pgp-signature
Content-Disposition: inline

-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.4.5 (FreeBSD)

iD8DBQFFPO9o7Nh7RM4TrhIRAh7eAJ9wd7faT038x78bWsQVG1yGciACyQCgm7Mo
RlUi5BODUKi2dGhV1+AiE8w=
=tGle
-----END PGP SIGNATURE-----

--J+xDcZ1j08+V/OfU--