From: David Vallner <david@...>
Date: 2006-12-03T19:53:36+09:00
Subject: Re: Simple and stuppid bug (can anyone find it?)

--------------enigC2A67252DAFBD93047DFE80A
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: quoted-printable

paul wrote:
> Hi all,
> I thought it to be good programming style to make attribute assignment
> chainable. When using the attr_writer an assignment returns te value
> assigned which is not what I want, so I tried to do-it-myself.
> The result is below. This doesn't work. When running Ruby gives:
> undefined method 'b=3D' for "AA":String (NoMethodError)
> Anybody, please tell me: *why*. What simple stuppid thing am I
> overseeing?
> Thanks in advance!
> Cheers,
> Paul
>=20
> --the code--
> class A
>   def initialize
>   end
>   def a
>     return @a
>   end
>   def a=3D(someA)
>     @a =3D someA
>     return self
>   end
>   def b
>     return @b
>   end
>   def b=3D(someB)
>     @b =3D someB
>     return self
>   end
> end
>=20
> puts A.new.a=3D("AA").b=3D("BB").a
> --the code--
>=20
>=20

There is no bug in your code, apparently Ruby always returns the rvalue
from what parses as an assignment.

With your class loaded into irb, I got:

irb(main):039:0> A.new.a=3D("AA")
=3D> "AA"

irb(main):043:0> A.new.send('a=3D', 'AA') # Does what you expected.
=3D> #<A:0x3b3015c @a=3D"AA">


So, can anyone recall a rationale for the behaviour (consistency with
mainstream programming languages with regards to assignment?) or is this
a Ruby bug?

Either way, disclaimer: I don't like what you're trying to do in the
first place. Pretty much anyone reading your code will expect assignment
to return the rvalue because that's what #attr_writer does, and the
chained assignment in your example just reads plain ugly to me,
especially since I subconsciously parse it as:
	A.new.a =3D "AA".b =3D "BB".a
i.e. ``assign "BB".a to -both- "AA".b and A.new.a''
and therefore am in favour of consistency with assignment in other
languages instead of consistency with Javaesque property setters (where
the ambiguity doesn't manifest.)

David Vallner


--------------enigC2A67252DAFBD93047DFE80A
Content-Type: application/pgp-signature; name="signature.asc"
Content-Description: OpenPGP digital signature
Content-Disposition: attachment; filename="signature.asc"

-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.4.5 (MingW32)

iD8DBQFFcqysy6MhrS8astoRAgD1AJ9oERqfAqkIwBT9VJYSnnSfluQFXwCfUBKb
24fEAPvL1iiULSF9paVZyys=
=i/Ea
-----END PGP SIGNATURE-----

--------------enigC2A67252DAFBD93047DFE80A--