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From: "joeloser at fastmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/105842] New: rejects-valid: static member function overload
 set constrained by concepts for class template results in ambiguous
 call
Date: Fri, 03 Jun 2022 21:04:44 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D105842

            Bug ID: 105842
           Summary: rejects-valid: static member function overload set
                    constrained by concepts for class template results in
                    ambiguous call
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: joeloser at fastmail dot com
  Target Milestone: ---

In the following snippet,

```
#include <concepts>
#include <cstddef>

template<class>
struct S {
  static constexpr auto f(const std::unsigned_integral auto value) ->
std::size_t {
    return {};
  }
  static constexpr auto f(const std::signed_integral auto value) -> std::si=
ze_t
{
    return f(static_cast<std::size_t>(value));
  }
};
```

The second `f` overload results in a compilation error:

```
error: call of overloaded =E2=80=98f(std::size_t)=E2=80=99 is ambiguous
... list of the two candidates
```

This appears to be a GCC bug, but only if S is a class template (regardless=
 of
whether the template parameter list is a type or a non-type). Note that cla=
ng
trunk compiles the code fine as-is. If `S` is a class and not a class templ=
ate,
then GCC accepts the code.

See it live at https://godbolt.org/z/oddxEWGMv=