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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/108736] [concepts] multidimensional subscript operator
 inside requires with variable template arguments is broken
Date: Thu, 09 Feb 2023 18:51:37 +0000
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X-Bugzilla-Component: c++
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D108736

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|[concepts] multidimensional |[concepts] multidimensional
                   |subscript operator reports  |subscript operator inside
                   |invalid error in requires   |requires with variable
                   |test                        |template arguments is
                   |                            |broken
             Status|UNCONFIRMED                 |NEW
     Ever confirmed|0                           |1
   Last reconfirmed|                            |2023-02-09

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Confirmed, even this is rejected:
```
    auto foo(auto a, auto... i) -> decltype(auto) {
        if constexpr (requires { a[i...]; }) {
            return a[i...];
        }
        else {
            return a;
        }
    }

    int x =3D foo(1, 1);
```

Note clang just ICEs.
Also the above works if it is not a variable argument auto ...

That is:
```
template<typename T, typename T1>
    auto foo(T a, T1 i) {
        if constexpr (requires { a[i]; }) {
            return a[i];
        }
        else {
            return a;
        }
    }

    int x =3D foo(1, 1);
```
Compiles just fine.=