On 30 March 2017 at 19:14, Agustín Bergé <agustinberge_at_[hidden]> wrote:

> LWG2911 gave us the new `is_aggregate` trait, but no feature-test macro.
> I would like to suggest `__cpp_lib_is_aggregate`. What follows is a
> motivational use case, courtesy of Jonathan Wakely:
>
> #include <vector>
> template<typename T, typename... Args>
> T make(Args&&... args)
> {
> #if __cpp_lib_is_aggregate
> if constexpr (std::is_aggregate_v<T>)
> return { std::forward<Args>(args)... };
> else
> #endif
> return T(std::forward<Args>(args)...);
> }
> struct Agg { int i; };
> int main()
> {
> auto v = make<std::vector<int>>(1, 2);
> #if __cpp_lib_is_aggregate
> // make<> only supports aggregates if std::is_aggregate is
> available
> auto a = make<Agg>(1);
>

What does the #else look like here? I'm not yet seeing how this feature
test macro is useful.

     #endif
> }
>
> Regards,
> --
> Agustín K-ballo Bergé
> http://talesofcpp.fusionfenix.com
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