2017-05-28 18:16 GMT+03:00 Ted Unangst <t...@tedunangst.com>:
> Vadim Zhukov wrote:
>> While working on getting Boost & its friends work under Clang,
>> I've stumbled upon the code that looks like the following:
>>
>> decltype(x, y) z = w;
>
> why not espie's fix from earlier?
Because I've missed it. :( I have no idea why espie@ did it this way, though...
And what's more interesting we shouldn't get into this code when
compiling with Clang. This should happen only for old GCCs. See the
program:
#define _LIBCPP_HAS_NO_DECLTYPE
#include <vector>
int main() {
int x;
double y;
decltype(x, y) z = y;
}
If you comment out the first line, it compiles fine under Clang. So
basically the problem only raises when the program being compiled
plays dirty games with _GNU_VER or something like that...
> but clang++ has variadic macros, like C99... the following patch allows
> macro decltype() to work a lot more like builtin __decltype in pre-C++11
>
> (note that still works with -std=c++98 -pedantic, much to my surprise, but
> which is cool)
>
> Index: __config
> ===================================================================
> RCS file: /cvs/src/lib/libcxx/include/__config,v
> retrieving revision 1.3
> diff -u -p -r1.3 __config
> --- __config 19 Sep 2016 22:17:22 -0000 1.3
> +++ __config 5 May 2017 15:21:58 -0000
> @@ -670,7 +670,7 @@ template <unsigned> struct __static_asse
> #ifdef _LIBCPP_HAS_NO_DECLTYPE
> // GCC 4.6 provides __decltype in all standard modes.
> #if !__is_identifier(__decltype) || _GNUC_VER >= 406
> -# define decltype(__x) __decltype(__x)
> +# define decltype(__x, ...) __decltype(__x, ##__VA_ARGS__)
> #else
> # define decltype(__x) __typeof__(__x)
> #endif
>
--
WBR,
Vadim Zhukov
