[Bug c++/115769] Implement CWG 2867 - Order of initialization for structured bindings

[jakub at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115769

--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Better testcase:
// CWG2867 - Order of initialization for structured bindings.
// { dg-do run { target c++17 } }

#define assert(X) do { if (!(X)) __builtin_abort(); } while (0)

namespace std {
  template<typename T> struct tuple_size;
  template<int, typename> struct tuple_element;
}

int c;
int i;

struct A {
  A () { assert (c == 3); ++c; }
  ~A () { assert (c == 12); ++c; }
  template <int I> int &get () const { assert (c == 5 + I); ++c; return i; }
};

template <> struct std::tuple_size <A> { static const int value = 4; };
template <int I> struct std::tuple_element <I, A> { using type = int; };
template <> struct std::tuple_size <const A> { static const int value = 4; };
template <int I> struct std::tuple_element <I, const A> { using type = int; };

struct B {
  B () { assert (c >= 1 && c <= 2); ++c; }
  ~B () { assert (c >= 9 && c <= 10); ++c; }
};

A
foo (const B &, const B &)
{
  A a;
  assert (c == 4);
  ++c;
  return a;
}

int
main ()
{
  {
    c = 1;
    const auto &[x, y, z, w] = foo (B {}, B {});
    assert (c == 11);
    ++c;
  }
  assert (c == 13);
}