From: Aaron Patterson <tenderlove@...>
Date: 2012-03-01T08:08:32+09:00
Subject: [ruby-core:43030] return values of methods on String subclasses


--huq684BweRXVnRxX
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
Content-Transfer-Encoding: quoted-printable

It pains me to ask about this, but since Rails subclasses String, I need
to ask some questions.

If you call a method that returns a substring on an instance of a
subclass of string, the subclass is returned:

    class TranslatedString < String
    end
   =20
    TranslatedString.new("omg")[0,1].class # =3D> TranslatedString

That's fine, except that if the String subclass implements initialize,
the initialize method is never called on the new object:


    class TranslatedString < String
      def initialize str
        super
        @not_translated =3D true
      end

      def translated?
        !@not_translated
      end
    end
   =20
    TranslatedString.new("omg").translated?      # =3D> false
    TranslatedString.new("omg")[0,1].translated? # =3D> true

This leaves us with instances of TranslatedString whose internal state is
incorrect because it had no chance to set up it's internal state.  Why
do we have this behavior?

I would like to propose that we either:

1: Only return instances of String (as a superclass implementation)

OR

2: Have `initialize_copy` or some other method called when the new
string subclass is created.

I prefer number #2.

Here is a patch for #2.  It may be naive, but my test passes:

  https://gist.github.com/1945213

Thanks.

--=20
Aaron Patterson
http://tenderlovemaking.com/

--huq684BweRXVnRxX
Content-Type: application/pgp-signature

-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.4.11 (Darwin)

iQEcBAEBAgAGBQJPTq6xAAoJEJUxcLy0/6/GZfAH/iYUC46kp3X08yAJhufQLHa/
9e1iYk7Ho+8prppkCXxmBpZUzo3B6YdfkSRztTGdU7OzQia/I/tNKAJ/5MIAdWap
WOobScp1/8jrRs9ijyaKaDabk3MVsByvDx0dFKt/HlQoIy+sPAKMM8fzsVYP/NJh
xplplBh8VbAu9+sYCEem39hXgU9L2jngJnkEG2BR6nw6G3nvUH+HOTc8CddSHApl
pijn8bePlk01WaOIHyO+s352To9jtCagIQ27ojAfKIds5HTNt+YmxZIo/GPgXxMJ
VIICwqu/ySdE+RrEwQNOeolNbO9mIp/TZEQE/O5HWDwFtIupIGH0sEBmrYzkzW4=
=BCA3
-----END PGP SIGNATURE-----

--huq684BweRXVnRxX--