[v3 PATCH] LWG 2766, LWG 2749

[Ville Voutilainen]

On 22 November 2016 at 15:36, Jonathan Wakely <jwakely@redhat.com> wrote:
>> +#if __cplusplus > 201402L || !defined(__STRICT_ANSI__) // c++1z or
>> gnu++11
>> +  template<typename _T1, typename _T2>
>> +    inline
>> +    typename enable_if<__not_<__and_<__is_swappable<_T1>,
>> +                                    __is_swappable<_T2>>>::value>::type
>> +    swap(pair<_T1, _T2>&, pair<_T1, _T2>&) = delete;
>
>
> Is there any advantage to using __not_ here, rather than just:
>
>    typename enable_if<!__and_<__is_swappable<_T1>,
>                               __is_swappable<_T2>>::value>::type
>
> ?
>
> __not_ is useful as a sub-expression of an __and_ / __or_ expression,
> but at the top level doesn't seem to buy anything, and is more typing,
> and requires indenting the code further.


There's no particular advantage, it's just a habitual way to write a mixture of
__and_s and __not_s that I suffer from, whichever way the nesting is.
I'm also not consistent:

+    inline enable_if_t<!(is_move_constructible_v<_Tp> && is_swappable_v<_Tp>)>
+    swap(optional<_Tp>&, optional<_Tp>&) = delete;

so I can certainly change all these swaps to use operator! rather than
__not_. Is the
patch otherwise ok for trunk? What about the tuple part?