2017-05-28 18:35 GMT+03:00 Vadim Zhukov <persg...@gmail.com>:
> 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...
Ah, now I've got it: it's compiling without -std=c++11 which triggers error.
I.e., when run:
clang++ x.cpp -o x
you'll get error with current __config, and won't with patched. And
this is how we compile boost - without c++11. And it's likely will be
a pain and ever likely break stuff, if we'll switch boost to c++11
mode, since we'll have to switch all software depending on boost,
either directly or indirectly (that's a really big number!), to eg++
on non-clang archs...
>> 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
--
WBR,
Vadim Zhukov
