MSVC in /std:c++latest mode rejects the code as ambiguous, but not in C++17
mode, nor do GCC/Clang in any mode...

https://gcc.godbolt.org/z/PzYWKxj8s

I would guess it might be a bug in MSVC.

On Tue, 28 Sept 2021 at 13:16, Vladimir Grigoriev via Std-Discussion <
std-discussion_at_[hidden]> wrote:

> I know that they are ambiguous. I have pointed out that it looks like a
> contradiction and unexpected behavior. It would be more natural if in
> the second case also the second function would be selected.
>
> With best regards,
> (Vlad from Moscow)
> You can meet me at http://cpp.forum24.ru/ or www.stackoverflow.com or
> http://ru.stackoverflow.com
>
>
>
> Вторник, 28 сентября 2021, 5:39 +03:00 от jim x <xmh970252187_at_[hidden]>:
>
>
>
> Vladimir Grigoriev via Std-Discussion <std-discussion_at_[hidden]
> <//e.mail.ru/compose/?mailto=mailto%3astd%2ddiscussion_at_[hidden]>>
> 于2021年9月28日周二 上午12:23写道：
>
> In my opinion there is some inconsistence in the function overload
> resolution when a function parameter has a referenced array type.
>
> Let assume that we have two functions
>
> void f( const ( &a )[] );
>
> and
>
> void f( const ( &a )[2] );
>
> If to write
>
> f( { 1, 2 } );
>
> then the second function will be selected.
>
> However if to write
>
> int a[2];
>
> and then
>
> f( a );
>
> then the compiler will issue an error relative to an ambiguity.
>
> It would be more natural if in this case also the second function would be
> selected.
>
> With best regards
> (Vlad from Moscow)
>
>
>
>
> You can meet me at http://cpp.forum24.ru/ or www.stackoverflow.com or
> http://ru.stackoverflow.com
> --
> Std-Discussion mailing list
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> https://lists.isocpp.org/mailman/listinfo.cgi/std-discussion
>
>
>
> For the first example, [over.ics.rank] p3 explicitly says that the second
> viable function is better than the first one
> > Two implicit conversion sequences of the same form are
> indistinguishable conversion sequences unless one of the following rules
> applies:
> >> -[...]
> >> L1 and L2 convert to arrays of the same element type, and either the
> number of elements
> n1 initialized by L1 is less than the number of elements n2 initialized
> by L2, or n1=n2 and L2 converts to an array of unknown bound and L1 does
> not,
>
>
> For the second case, they are all governed by [dcl.init.ref#5.1]
> > If the reference is an lvalue reference and the initializer expression
> >> is an lvalue (but is not a bit-field), and “cv1 T1” is
> reference-compatible with “cv2 T2”, or
>
> -
>
> pointer to an array of unknown bound of const int is reference-compatible
> with a pointer to an array of 2 int (via qualification conversion).
> Regardless of `#1` or `#2`, they are identity conversion in reference
> binding as per [over.ics.ref] p1, and they cannot be distinguishable by
> [over.ics.rank] and [over.match.best.general], so they are ambiguous.
>
>
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-- 
Yongwei Wu
URL: http://wyw.dcweb.cn/