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From: "ppalka at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug libstdc++/110853] [c++-concepts] Bad interaction between
 deduction guide with decay and constraints
Date: Mon, 07 Aug 2023 14:08:18 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D110853

Patrick Palka <ppalka at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ppalka at gcc dot gnu.org

--- Comment #1 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Since as you mention a member function body is a complete-class context,
libstdc++'s std::pair implementation strategy does seem non-conforming in t=
his
case.

Clang seems to not propagate constructor constraints to the implicit deduct=
ion
guide, according to the following example, and is probably the reason why it
accepts your reduced example.

template<class T>
struct A {
  A(T) requires false; // #1
  A(...); // #2
};

auto a =3D A(0); // GCC rejects, Clang incorrectly(?) selects #2 with T=3Di=
nt.=