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From: "redi at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug c++/104699] zero-length-array is not considered as an array
Date: Mon, 28 Feb 2022 09:58:30 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D104699

--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> ---
The std::is_array result is a consequence of the compiler not matching the
is_array<T[N]> partial specialization for int[0]:

using size_t =3D decltype(sizeof(0));
template<typename T> struct X { static constexpr bool value =3D false; };
template<typename T, size_t N> struct X<T[N]> { static constexpr bool value=
 =3D
true; };
static_assert( ! X<int[0]>::value );

GCC, Clang, Intel and MSVC all agree here: the int[0] type does not match t=
he
X<T[N]> partial specialization.

I don't think it would be reasonable for the library to work differently, a=
nd I
don't think it's reasonable to add kluges to make_shared to support creatin=
g an
object of a type that should only exist as a subobject of some other object=
.=