lichray marked an inline comment as done.
lichray added a comment.
In https://reviews.llvm.org/D44865#1048880, @EricWF wrote:
> Has this paper been adopted into the standard yet?
No. However, it cleanly passed LEWG for recommending a DR against C++17, so I
think we can apply it early, just like we sometimes make changes before filing
issues :)
================
Comment at: include/variant:1109
+#define _LIBCPP_VARIANT_BOOLEAN_CONVERSION(bool_type) \
+ template <class... _Types> \
----------------
EricWF wrote:
> EricWF wrote:
> > I would like to see a version of this patch that doesn't use preprocessor
> > expansion to specialize `__overload` multiple times.
> >
> > Perhaps adding a `bool = is_same<remove_cv_t<First>, bool>` to `__overload`
> > and then specializing once on that?
> Or perhaps SFINAE-ing the `test` member instead of specializing `__overload`.
>
> Something like this maybe?
>
> ```
>
> template <class _Tp, class... _Types>
> struct __overload< _Tp, _Types...> : __overload<_Types...>
> {
> using __overload<_Types...>::operator();
>
> template <bool _EnableBool>
> using _DepIsBool = typename __dependent_type<
> enable_if<is_same_v<remove_cv_t<_Tp>, bool> == _EnableBool>,
> _EnableBool
> >::type;
>
> template <class _Up, bool _EnableBool = false, class =
> _DepIsBool<_EnableBool>>
> auto operator()(_Tp, _Up&& __t) const
> -> decltype(_Tp{__t}, __identity<_Tp>());
>
> template <class _Up, class _Ap = __uncvref_t<_Up>,
> bool _EnableIfBool = true, class = _DepIsBool<_EnableIfBool>>
> auto operator()(bool, _Up&&, int _Ap::*) const
> -> __identity<_Tp>;
>
> template <class _Up, class _Ap = __uncvref_t<_Up>,
> bool _EnableIfBool = true, class = _DepIsBool<_EnableIfBool>>
> auto operator()(bool, _Up&&) const
> -> enable_if_t<is_same_v<_Ap, bool>, __identity<_Tp>>;
> };
>
> ```
If we have concepts we can do so, but `__overload` is already variadic, leaving
no space for sfinae...
Repository:
rCXX libc++
https://reviews.llvm.org/D44865
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