Re: extending c++ classes and enumerations
perrog@gmail.com wrote:
I have some question about a C++ syntax that can extend classes and
enumerations. A modern language should support this. :-) I'm asking
because there seems to be a dozen c++ entusiasts reading this group,
and I guess this is the right place to go, perhaps resulting in finding
support, new friends or whatever. :-)
To put myself shortly,
* extending instance member fields (autos and volatiles) and instance
functions (virtuals) would be an error.
* Extending static functions and fields and non-virtual functions
would be legatime.
* Extending enumeration automatically starts the increment from the
previously enumeration definition.
Has this been discussed before? Has anyone other thought about this? If
you have, you are welcome to exchange ideas with me. ;-)
You've got this already, just with a slightly different syntax.
Use the keyword struct, instead of class, and use free functions
taking a pointer to the type as first parameter, rather than
member functions. You can extend to your hearts desire.
Of course, encapsulation sort of takes a beating. Classes were
introduced into C++ exactly to prevent this sort of thing.
(There is a slight argument for being able to add private
non-virtual member functions, but not enough to make it worth
writing up a proposal. There is also some argument for being
able to allow non-member functions to be called with member
function syntax, and vice versa. I don't know that it's
conclusive, however.)
In the case of enum's, of course, I doubt that it's
implementable. The compiler needs to know all of the values of
an enum in order to know the size of an instance of the enum (or
even the size of a pointer to an instance, on some machines).
--
James Kanze (GABI Software) email:james.kanze@gmail.com
Conseils en informatique orientie objet/
Beratung in objektorientierter Datenverarbeitung
9 place Simard, 78210 St.-Cyr-l'Icole, France, +33 (0)1 30 23 00 34
--
[ See http://www.gotw.ca/resources/clcm.htm for info about ]
[ comp.lang.c++.moderated. First time posters: Do this! ]