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From: Alf P. Steinbach on 10 Dec 2009 21:23
* Kaz Kylheku:
> On 2009-12-11, Alf P. Steinbach <alfps(a)start.no> wrote:
>> * Kaz Kylheku:
>>> On 2009-12-11, Alf P. Steinbach <alfps(a)start.no> wrote:
>>>>> On 2009-12-10, Alf P. Steinbach <alfps(a)start.no> wrote:
>>>>>> You loose the ability to assert that you're overriding something
>>>>>> existing.
>>> [ ... ]
>>>
>>>> Nobody's said that you can assert that you're overriding, so that's a straw man
>>> ?
>> You're quoting the wrong context.
>>
>> In my first statement, the meaning of "overriding something existing" which I
>> said one can do, was with the accent on the something existing, otherwise
>> there'd be no point in adding those words; you know that you're overriding,
>> you're asserting that the func you're overriding does exist in base class, and
>> that assertion serves as documentation and guards against code changes.
>
> Okay, can you show how you are coding that?

#define CPPX_IS_OVERRIDE_OF_0ARG( memberSpec ) \
::cppx::suppressUnusedWarning( sizeof( (memberSpec(), 0) ) )
#define CPPX_IS_OVERRIDE_OF_1ARG( memberSpec, a1 ) \
::cppx::suppressUnusedWarning( sizeof( (memberSpec(a1), 0) ) )
#define CPPX_IS_OVERRIDE_OF_2ARG( memberSpec, a1, a2 ) \
::cppx::suppressUnusedWarning( sizeof( (memberSpec(a1, a2), 0) ) )

#define CPPX_IS_OVERRIDE_OF( memberSpec ) CPPX_IS_OVERRIDE_OF_0ARG( memberSpec )


Note that the macro name doesn't say what the macro does.

It's just a documentation macro outfitted with some checking that doesn't hurt
if what it documents is true.

Instead of individual args you can better use just an arg-list argument, but the
code above didn't start out that way and there's been no reason to fix it.


> If we simply declare a function in a class which has bases, we don't
> know whether or not that function is virtual; it could match a virtual
> function in one of the bases, thereby inheriting that attribute
> and overriding.
>
> If we explicitly make it virtual, we still don't know whether or not
> something is being overridden, or whether it's a new virtual.
>
> We can inspect all the bases when we are coding this, but tomorrow, they
> can change; someone can add a virtual function to a base such that
> we already have an overriding function in the derived class.

I think that's right, that there's no portable way to detect virtualness of a
specific member routine in a C++98.


> If there is a way of writing assertions for this sort of thing, or
> anyting at all related to overriding or not-overriding; that could be
> useful. (Compile time, or run-time).

I don't think so, not in a portable way.


Cheers & hth.,

- Alf
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