[Bug c++/113308] New: derived class doesn't currently allow inherited explicit object member function post increment operator

[Bug c++/113308] New: derived class doesn't currently allow inherited explicit object member function post increment operator

[cooky.ykooc922 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113308

            Bug ID: 113308
           Summary: derived class doesn't currently allow inherited
                    explicit object member function post increment
                    operator
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: cooky.ykooc922 at gmail dot com
  Target Milestone: ---

With the recent support of explicit object parameter functions, inheriting
explicit object member functions from base class seems to work except for post
increment operator 'operator++(int)'.

struct add_fn
{
    template <typename Self>
    Self operator++(this Self&& self, int)
    {
      auto temp = self;
      ++self;
      return temp;
    }
};

struct A : add_fn 
{
    int n;
    A(int n) : n(n) {}

    A& operator++() 
    {
      ++n;
      return *this;
    }

    // this doesn't work either:
    // A& operator++(this A& self)
    // {
    //   ++self.n;
    //   return self;
    // }
};

int main()
{
    A a { 5 };
    ++a; // ok
    a++; // error: no 'operator++(int)' declared for postfix '++'
}

godbolt link: https://godbolt.org/z/1h57Thvds

[Bug c++/113308] derived class doesn't currently allow inherited explicit object member function post increment operator

[nathanieloshead at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113308

Nathaniel Shead <nathanieloshead at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |nathanieloshead at gmail dot com

--- Comment #1 from Nathaniel Shead <nathanieloshead at gmail dot com> ---
I believe this is correct behaviour: The definition of `operator++` in the
child class hides the `operator++` declared in the base class. Similarly to the
following code:


struct base {
  void f(int) {}
};
struct d1 : base {
  void f() {}
};
struct d2 : base {
  using base::f;  // explicitly add base::f as an overload
  void f() {}
};

int main() {
  d1{}.f(10);  // error
  d2{}.f(10);  // OK
}

[Bug c++/113308] derived class doesn't currently allow inherited explicit object member function post increment operator

[waffl3x at protonmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113308

--- Comment #2 from waffl3x <waffl3x at protonmail dot com> ---
(In reply to Nathaniel Shead from comment #1)
> I believe this is correct behaviour: The definition of `operator++` in the
> child class hides the `operator++` declared in the base class. Similarly to
> the following code:
> 
> 
> struct base {
>   void f(int) {}
> };
> struct d1 : base {
>   void f() {}
> };
> struct d2 : base {
>   using base::f;  // explicitly add base::f as an overload
>   void f() {}
> };
> 
> int main() {
>   d1{}.f(10);  // error
>   d2{}.f(10);  // OK
> }

I'm pretty sure Nathaniel is right,
https://godbolt.org/z/d4r3dTsqa
https://godbolt.org/z/sxz1rcGbb
Mind you, clang and msvc's implementations are buggier than mine so I'm
not going to say "doesn't work on theirs so it isn't a bug" but I don't
think this one is a bug.

Thank you for testing my patch though, I do appreciate it.

[Bug c++/113308] derived class doesn't currently allow inherited explicit object member function post increment operator

[waffl3x at protonmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113308

--- Comment #3 from waffl3x <waffl3x at protonmail dot com> ---
I meant to post this link instead of one of the others.
https://godbolt.org/z/oMP8185Yh
I guess I shouldn't be replying to things while still waking up, sorry!

[Bug c++/113308] derived class doesn't currently allow inherited explicit object member function post increment operator

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113308

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |INVALID
             Status|UNCONFIRMED                 |RESOLVED

--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Yes, I think gcc is correct here. Explicit object functions aren't immune to
name hiding.