Eric Lemings wrote:
>
>
>> -----Original Message-----
>> From: Travis Vitek [mailto:Travis.Vitek@roguewave.com]
>> Sent: Monday, June 23, 2008 4:59 PM
>> To: dev@stdcxx.apache.org
>> Subject: RE: svn commit: r668225 -
>> /stdcxx/branches/4.3.x/etc/config/src/VA_LIST_FUNC_MACRO.cpp
>>
>>
>>
>>> Eric Lemings wrote:
>>>
>>>> Martin Sebor wrote:
>>>>
>>>>
>>>> My point was that I couldn't find a way to use a feature
>>>> that depends on variadic macros on platforms where they
>>>> are not supported. In other words, I can't picture what
>>>> the #else branch below would look like:
>>>>
>>>> #ifndef _RWSTD_NO_VARIADIC_MACROS
>>>> # define RW_ASSERT(expr, ...) \
>>>> rw_assert (expr, 0, __LINE__, __VA_LIST__)
>>>> #else
>>>> # define RW_ASSERT(expr, ???) ...
>>>> #endif
>>> You're right. There is no backward-compatible workaround which
>>> essentially rules out using variadic macros in these cases.
Which is why I don't think we'll be able to (or need to) use the
config macro in our code.
>>>
>> I think I've showed this trick before, but it won't work with template
>> parameters, only function parameters.
Right. This "trick" obviates the need for variadic macros in the
case of the rw_xxx() functions.
(Note that the trick isn't a general replacement for variadic macros
because it relies on a runtime mechanism while variadic macros are
a compile-time one.)
>>
>> struct Variadic
>> {
>> void operator()(const char* fmt, ...);
>> };
>>
>> #define VARIADIC Variadic().operator()
>>
>> Of course you would use it like this...
>>
>> VARIADIC("hello %s", "world!");
>
> Had forgotten about that. :)
>
> So, we have something like this:
There's no need for the additional complexity when we can just use
the #else case unconditionally. The !_RWSTD_NO_VARIADIC_MACROS case
provides no advantage over the workaround.
>
> #ifndef _RWSTD_NO_VARIADIC_MACROS
> # define RW_ASSERT(expr, ...) \
> rw_assert (expr, 0, __LINE__, __VA_LIST__)
> #else
> struct __rw_assert {
> int operator()(int expr, const char* file, int line,
> const char* fmt, ...) {
> va_list va;
> va_start (va, fmt);
> _rw_vdiag (diag_assert, 0 == expr, file, line, fmt, va);
> va_end (va);
> return success;
> }
> };
> # define RW_ASSERT __rw_assert().operator()
> #endif
>
> That pretty close?
>
> And why is there a 2nd parameter in rw_assert() if its never used? :P
>
> Brad.
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