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From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/92687] decltype of a structured binding to a tuple
 component is a reference type inside a template function
Date: Wed, 28 Feb 2024 12:15:05 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D92687

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jakub at gcc dot gnu.org

--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Testcase without using library:
namespace std {
  template<typename T> struct tuple_size;
  template<int, typename> struct tuple_element;
}

struct A {
  int i;
  template <int I> int& get() { return i; }
};

template<> struct std::tuple_size<A> { static const int value =3D 2; };
template<int I> struct std::tuple_element<I,A> { using type =3D int; };

template<typename T>
struct is_reference {
  static const bool value =3D false;
};

template<typename T>
struct is_reference<T&>
{
  static const bool value =3D true;
};

template<typename T>
struct is_reference<T&&>
{
  static const bool value =3D true;
};

template<int N>
void
foo ()
{
  auto [x, y] =3D A {};
  static_assert (!is_reference<decltype (x)>::value, "");
}

void
bar ()
{
  auto [x, y] =3D A {};
  static_assert (!is_reference<decltype (x)>::value, "");
}

template<typename T>
void
baz ()
{
  auto [x, y] =3D T {};
  static_assert (!is_reference<decltype (x)>::value, "");
}

void
qux ()
{
  foo<0> ();
  baz<A> ();
}

which shows it is only for the non-dependent structured binding in a templa=
te
case.=