[libcxx-commits] [PATCH] D135292: [libc++][format] Improves CTAD.

[Louis Dionne via Phabricator via libcxx-commits]

ldionne accepted this revision.
ldionne added inline comments.
This revision is now accepted and ready to land.


================
Comment at: libcxx/include/__config:1202
 
 // There are a handful of standard library types that are intended to support CTAD but don't need any
 // explicit deduction guides to do so. This macro is used to mark them as such, which suppresses the
----------------



================
Comment at: libcxx/include/__config:1206
 #if _LIBCPP_STD_VER >= 17
-#  define _LIBCPP_CTAD_SUPPORTED_FOR_TYPE(_ClassName)                                                                  \
-    template <class _Tag = void>                                                                                       \
-    _ClassName(typename _Tag::__allow_ctad) -> _ClassName<_Tag>
+#    define _LIBCPP_CTAD_SUPPORTED_FOR_TYPE(_ClassName)                                                                \
+      template <class _Tag = void>                                                                                     \
----------------
ldionne wrote:
> Can we instead try this?
> 
> ```
> #define _LIBCPP_CTAD_SUPPORTED_FOR_TYPE(_ClassName) \
>   template <class ..._Tag> \
>   _ClassName(typename _Tag::__allow_ctad...) -> _ClassName<_Tag...>;
> ```
> 
> Would that allow handling class templates that take any number of arguments?
In a follow-up patch, I think we could consider also renaming this macro to `_LIBCPP_CTAD_INTENDED_TO_WORK`? We can bikeshed on that but I think we can find something better than `_LIBCPP_CTAD_SUPPORTED_FOR_TYPE`.


================
Comment at: libcxx/include/__config:1206-1208
+#    define _LIBCPP_CTAD_SUPPORTED_FOR_TYPE(_ClassName)                                                                \
+      template <class _Tag = void>                                                                                     \
+      _ClassName(typename _Tag::__allow_ctad)->_ClassName<_Tag>
----------------
Can we instead try this?

```
#define _LIBCPP_CTAD_SUPPORTED_FOR_TYPE(_ClassName) \
  template <class ..._Tag> \
  _ClassName(typename _Tag::__allow_ctad...) -> _ClassName<_Tag...>;
```

Would that allow handling class templates that take any number of arguments?


Repository:
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  https://reviews.llvm.org/D135292/new/

https://reviews.llvm.org/D135292