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From: "redi at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug c++/91780] Discrepancy between gcc 7.4, through 9.2, compared
 to clang.
Date: Fri, 17 Dec 2021 10:46:59 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D91780

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|needs-reduction             |

--- Comment #8 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Reduced:

template<typename T> struct add_pointer { using type =3D T*; };
template<typename T> struct add_pointer<T&> { using type =3D T*; };
template<typename T> struct add_pointer<T&&> { using type =3D T*; };
template<typename T> using add_pointer_t =3D typename add_pointer<T>::type;

template<typename... T> struct first { };
template<typename T, typename... U> struct first<T, U...> { using type =3D =
T; };
template<typename... T> using first_t =3D typename first<T...>::type;

template <typename... Containers>
struct zip
{
    template <typename... Container_types>
    zip(Containers... containers) : containers_{ &containers... } { }

    add_pointer_t<first_t<Containers...>> containers_[sizeof...(Containers)=
];
};

template <typename... Container_types>
zip(Container_types&&... containers) -> zip<Container_types...>;

struct vector { int i =3D 0; };

int main()
{
  vector v1, v2;
  zip z(v1, v2);
  z.containers_[0]->i =3D 1;
  z.containers_[1]->i =3D 2;
  if (v1.i =3D=3D 0)
    throw 1;
}=