CWG Issue 2789

This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 118f. See http://www.open-std.org/jtc1/sc22/wg21/ for the official list.

2025-11-07

2789. Overload resolution with implicit and explicit object member functions

Section: 12.2.4.1 [over.match.best.general] Status: CD7 Submitter: Corentin Jabot Date: 2023-08-08

[Accepted as a DR at the November, 2023 meeting.]

Consider:

  template <typename T = int>
  struct S {
    constexpr void f();                      / #1
    constexpr void f(this S&) requires true; / #2
  };

  void test() {
    S<> s;
    s.f();                 / #3
  }

With the current rules, the call at #3 is ambiguous, even though #2 is more constrainted.

Proposed resolution (approved by CWG 2023-11-07):

Change in 12.2.4.1 [over.match.best.general] bullet 2.6 as follows:

...
F1 and F2 are non-template functions ~~with~~ and

they have the same ~~parameter-type-lists~~ non-object-parameter-type-lists (9.3.4.6 [dcl.fct]), and

if they are member functions, both are direct members of the same class, and

if both are non-static member functions, they have the same types for their object parameters, and

F1 is more constrained than F2 according to the partial ordering of constraints described in 13.5.5 [temp.constr.order],

or if not that,
[ Example:
  template <typename T = int>
  struct S {
    constexpr void f();                      / #1
    constexpr void f(this S&) requires true; / #2
  };

  void test() {
    S<> s;
    s.f();                 / calls #2
  }
-- end example ]
...