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| From | Seungbeom Kim<musiphil@bawi.org> |
|---|---|
| Newsgroups | comp.std.c++ |
| Subject | Re: New strongly type enum proposal featuring inherited enums |
| Date | 2011-08-24 14:06 -0700 |
| Organization | albasani.net |
| Message-ID | <j2fuat$u6f$1@usenet.stanford.edu> (permalink) |
| References | <4e49ea26$2@news.x-privat.org> |
On 2011-08-16 20:28, Phil Bouchard wrote:
>
> Is it too late to change the strongly type enum? I have a proposal
> that is much cleaner than what is on its way.
I'm afraid it is too late to change anything for C++0x.
But you can certainly propose something for the next standard.
> Right now we have:
> enum class Val: unsigned long { E1, E2, E3, E4 };
>
> Comments:
> 1) This design is bad because the ':' sign is reserved for inheritance.
The ':' sign had not been reserved for inheritance. Labels (including
case labels) use it, bit field declarations use it, ctor-initializers
use it, the ternary operator (?:) use it, and so on.
Furthermore, extending the meaning of a lexical element is common
as the language evolves.
>
> 2) Inheriting from another enum would be quite useful. For example:
> enum class Widget {button, combobox, listview};
> enum class SuperWidget : Widget {iconview}
>
> This way iconview would be equal to 3, not 0.
When class D inherits from class B, any D object can be regarded as a
B object; e.g. you can pass a D object to a function like f(B&).
Therefore, D is a subtype of B, i.e. D<: B.
When enum class SW "inherits" from enum class W, a SW object cannot be
regarded as a W object, but the converse holds: i.e. not SW<: W, but
W<: SW. In this regard, using the term "inheritance" for extending enum
classes as such may be confusing.
But this could be useful, still. I can even imagine something like this:
enum class WindowOptions : unsigned short { A, B, C };
enum class AdvancedWindowOptions : WindowOptions { D, E };
whose implications in full I'm not sure of yet.
>
> 3) Redefining the underlying type could be easily done with:
> enum class Val { unsigned long E1, E2, E3, E4 };
>
> This is much more neat and is similar to a declaration of multiple instances:
> const unsigned long E1, E2, E3, E4;
It looks similar to a simple-declaration, but its syntax must be
something entirely different. You can neither put a semicolon at
the end of the list of the enumerators, nor use different types
for different enumerators.
I think this is a case where a syntax that is too similar but not the
same can be more confusing than a syntax that looks different enough.
We might face questions like '"int i1, i2;" is equivalent to "int i1;
int i2;" but why isn't it the case inside an enum?'
Anyway, this is a matter of taste, after all.
--
Seungbeom Kim
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Back to comp.std.c++ | Previous | Next — Previous in thread | Next in thread | Find similar
New strongly type enum proposal featuring inherited enums Phil Bouchard <philippe@fornux.com> - 2011-08-16 21:28 -0600
Re: New strongly type enum proposal featuring inherited enums Daniel Krügler <daniel.kruegler@googlemail.com> - 2011-08-18 07:54 -0600
Re: New strongly type enum proposal featuring inherited enums Phil Bouchard<philippe@fornux.com> - 2011-08-24 14:06 -0700
Re: New strongly type enum proposal featuring inherited enums Daniel Krügler<daniel.kruegler@googlemail.com> - 2011-08-24 17:39 -0700
Re: New strongly type enum proposal featuring inherited enums Bart van Ingen Schenau<bart@ingen.ddns.info> - 2011-08-25 20:51 -0600
Re: New strongly type enum proposal featuring inherited enums =3D?ISO-8859-15?Q?Daniel_Kr=3DFCgler?=3D <daniel.kruegler@googlemail.= com> - 2011-09-07 11:08 -0700
Re: New strongly type enum proposal featuring inherited enums Miles Bader <miles@gnu.org> - 2011-09-08 14:46 -0700
Re: New strongly type enum... why not use "using"? "peter miller"<fuchsia.groan@virgin.net> - 2011-09-12 11:18 -0700
Re: New strongly type enum... why not use "using"? Miles Bader<miles@gnu.org> - 2011-09-13 09:29 -0700
Re: New strongly type enum... why not use "using"? "peter miller"<fuchsia.groan@virgin.net> - 2011-09-15 14:13 -0700
Re: New strongly type enum proposal featuring inherited enums Pete Becker <pete@versatilecoding.com> - 2011-08-18 07:51 -0600
Re: New strongly type enum proposal featuring inherited enums Victor Bazarov<v.bazarov@comcast.invalid> - 2011-08-24 14:06 -0700
Re: New strongly type enum proposal featuring inherited enums Paavo Helde<myfirstname@osa.pri.ee> - 2011-08-24 14:06 -0700
Re: New strongly type enum proposal featuring inherited enums Francis Glassborow<francis.glassborow@btinternet.com> - 2011-08-24 14:52 -0700
Re: New strongly type enum proposal featuring inherited enums Phil Bouchard<philippe@fornux.com> - 2011-08-24 17:39 -0700
Re: New strongly type enum proposal featuring inherited enums Alain Ketterlin <alain@dpt-info.u-strasbg.fr> - 2011-08-18 07:53 -0600
Re: New strongly type enum proposal featuring inherited enums Phil Bouchard<philippe@fornux.com> - 2011-08-24 14:52 -0700
Re: New strongly type enum proposal featuring inherited enums Marcel Müller <news.5.maazl@spamgourmet.com> - 2011-08-18 07:52 -0600
Re: New strongly type enum proposal featuring inherited enums Phil Bouchard<philippe@fornux.com> - 2011-08-23 18:20 -0700
Re: New strongly type enum proposal featuring inherited enums Phil Bouchard <philippe@fornux.com> - 2011-08-24 14:52 -0700
Re: New strongly type enum proposal featuring inherited enums Phil Bouchard <philippe@fornux.com> - 2011-08-24 14:52 -0700
Re: New strongly type enum proposal featuring inherited enums Francis Glassborow<francis.glassborow@btinternet.com> - 2011-08-24 14:06 -0700
Re: New strongly type enum proposal featuring inherited enums "Bo Persson"<bop@gmb.dk> - 2011-08-24 14:06 -0700
Re: New strongly type enum proposal featuring inherited enums red floyd<no.spam.here@its.invalid> - 2011-08-24 14:06 -0700
Re: New strongly type enum proposal featuring inherited enums Seungbeom Kim<musiphil@bawi.org> - 2011-08-24 14:06 -0700
Re: New strongly type enum proposal featuring inherited enums Phil Bouchard<philippe@fornux.com> - 2011-08-24 17:39 -0700
Re: New strongly type enum proposal featuring inherited enums Phil Bouchard<philippe@fornux.com> - 2011-08-24 17:40 -0700
Re: New strongly type enum proposal featuring inherited enums Phil Bouchard<philippe@fornux.com> - 2011-08-24 17:40 -0700
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