Re: [boost] [config] local types as template params

Subject: Re: [boost] [config] local types as template params
From: Vicente J. Botet Escriba (vicente.botet_at_[hidden])
Date: 2012-01-07 09:42:41

Le 07/01/12 11:23, Lorenzo Caminiti a écrit :
> On Thu, Jan 5, 2012 at 1:00 PM, Mathias Gaunard
> <mathias.gaunard_at_[hidden]>  wrote:
>> On 01/02/2012 10:58 AM, Lorenzo Caminiti wrote:
>>> Hello all,
>>>
>>> Is it possible to add a macro
>>> BOOST_CONFIG_LOCAL_TYPES_AS_TEMPLATE_PARAMS to Boost.Config to
>>> indicate if local types can be passed as template parameters?
>>>
>>> 1) Boost.Closure (formerly, Boost.Local) implements some optimizations
>>> when local types can be passed as template parameters.
>>> 2) C++11 always allows to pass local types as template parameters.
>>> 3) Local types cannot be passed as template parameters on C++03
>>> instead but some C++03 compilers MSVC 8 (and older?) allow it anyway.
>>>
>>> // If it is possible to pass local types (classes, etc) as template
>>> parameters.
>>> // This is not possible in pure C++03 but it is possible in some C++03
>>> // extensions (MSVC 8.0) and with C++11 (GCC>= 4.5.x -std=c++0x).
>>> #if (__GNUC__>    4 || (__GNUC__ == 4&&    __GNUC_MINOR__>    4))&&    \
>>>          defined(__GXX_EXPERIMENTAL_CXX0X__)
>>>      // From GCC 4.5.x when -std=c++0x specified.
>>> #   define BOOST_LOCAL_TYPES_AS_TEMPLATE_PARAMS
>>> #elif defined(_MSC_VER)
>>>      // For (all?) MSVC (tested on MVSC 8.0).
>>> #   define BOOST_LOCAL_TYPES_AS_TEMPLATE_PARAMS
>>> #endif
>>
>> Boost.Config is not organized like that, it's per compiler.
> I see, I will add the macro to the relative compiler's header.
>
>> the name should also be BOOST_NO_LOCAL_TYPES_AS_TEMPLATE_PARAMS.
> OK (even if the macro will be defined by default on C++03 compilers
> unless tested otherwise-- in other words, it is the most conservative
> to define the macro on C++03).
>
>> Finally this seems incomplete, local types as template params used to work
>> in C++03 with older versions of GCC too.
>> It does indeed work for all versions of MSVC AFAIK.
> Yes, it's incomplete... Can someone with access to many compilers and
> compiler versions try to compile the example below and let me know if
> it compiles? (I only have access to MSVC 8.0 and GCC 4.5.3).
>
> #include<algorithm>
> #include<iostream>
>
> int main() {
>     struct s {
>         void operator()(int x) {
>             std::cout<<  x<<  std::endl;
>         }
>     } l;
>
>     int nums[] = {1, 2, 3};
>     std::for_each(nums, nums + 3, l);
>
>     return 0;
> }
>
> Thanks a lot.
> --Lorenzo
>
Lorenzo,

I suggest you to follow the process (see 
http://www.boost.org/doc/libs/1_48_0/libs/config/doc/html/boost_config/guidelines_for_boost_authors.html) 
to add new macros and propose a patch for the trunk to John.

In this way you will have the results for all the trunk testers.

Best,
Vicente