From: "Esteban Manchado Velázquez" <zoso@...>
Date: 2006-05-03T17:28:48+09:00
Subject: Re: Constant in Ruby.

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Hi Charlie,

On Sun, Apr 30, 2006 at 03:57:41PM +0900, Charlie wrote:
> [...]
> > It's constant in that you can't reassign a different instance to the=20
> > same name (try setting X =3D 10 after you've set it to 20 and Ruby will=
=20
> > gripe).  The instances themselves may still be mutable (see=20
> > Object#freeze if you want to change that).
>=20
> okay, I just try this:
>=20
> X =3D 20
> X =3D 10
> puts(X)
> 10
> X.freeze
> X =3D 30
> puts(X)
> 30

    The "freeze" doesn't let the object change, but in this case you're not
changing the object, you're changing the reference.

    Let's see if an example clears it up:

------------------------------------- 8< ----------------------------------=
---
irb(main):001:0> X =3D "hi"
=3D> "hi"
irb(main):002:0> X =3D "hello"
(irb):2: warning: already initialized constant X
=3D> "hello"
irb(main):003:0> X.sub!(/$/, "!")
=3D> "hello!"
irb(main):004:0> X.freeze
=3D> "hello!"
irb(main):005:0> X.sub!(/e/, "a")
TypeError: can't modify frozen string
        from (irb):5:in `sub!'
        from (irb):5
irb(main):006:0>
------------------------------------- >8 ----------------------------------=
---

You can't reassign a constant (without a warning), and you can't change an
_object_ (possibly, but not necessarily, pointed to by a constant) that has
been frozen.

    HTH,

--=20
Esteban Manchado Vel=E1zquez <zoso@foton.es> - http://www.foton.es
EuropeSwPatentFree - http://EuropeSwPatentFree.hispalinux.es

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