[Bug c++/97198] __is_constructible(int[], int) should return true

[lichray at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97198

--- Comment #8 from Zhihao Yuan <lichray at gmail dot com> ---
(In reply to Jonathan Wakely from comment #7)
> (In reply to Zhihao Yuan from comment #5)
> > Encountered this today. In case I cannot show up when discussing LWG3486, my
> > use case is that C(in_place_type<T[]>, a, b, c) should "just works." It's up
> > to C how to deal with it. In my case, it's new T[].
> 
> I was going to add a note to the issue, but I don't know what to add. What
> is C? Why wouldn't it work today? Why does std::is_constructible affect it?

I meant to let C stand for some type C's constructor here. I wanted to express
the following: in_place_type is often used by type-erasures to forward all
information that is expression-equivalent to some form of initialization. Let's
say I want to create an object of type C with

  C obj(in_place_type<U>, a, b, c);

where obj erases the type of a hypothetical object created in

  U x(a, b, c);

Because type erasure means to erase the U in in_place_type<U>, it doesn't
matter if U != decltype(x). It works according to the literal interpretation of
the standard today. But if we say std::is_constructible_v<int[], int, int, int>
== false, extra efforts are needed to restore the meaning of in_place_type.