From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-bugzilla@gcc.gnu.org>
Received: by sourceware.org (Postfix, from userid 48)
 id 13E783853C0D; Mon,  2 Aug 2021 09:14:07 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 13E783853C0D
From: "redi at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/24847] Instantiates un-called copy constructor
Date: Mon, 02 Aug 2021 09:14:06 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: changed
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: c++
X-Bugzilla-Version: 3.4.0
X-Bugzilla-Keywords: rejects-valid
X-Bugzilla-Severity: normal
X-Bugzilla-Who: redi at gcc dot gnu.org
X-Bugzilla-Status: NEW
X-Bugzilla-Resolution: 
X-Bugzilla-Priority: P3
X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org
X-Bugzilla-Target-Milestone: ---
X-Bugzilla-Flags: 
X-Bugzilla-Changed-Fields: 
Message-ID: <bug-24847-4-ExUp2eKR0m@http.gcc.gnu.org/bugzilla/>
In-Reply-To: <bug-24847-4@http.gcc.gnu.org/bugzilla/>
References: <bug-24847-4@http.gcc.gnu.org/bugzilla/>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/
Auto-Submitted: auto-generated
MIME-Version: 1.0
X-BeenThere: gcc-bugs@gcc.gnu.org
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: Gcc-bugs mailing list <gcc-bugs.gcc.gnu.org>
List-Unsubscribe: <https://gcc.gnu.org/mailman/options/gcc-bugs>,
 <mailto:gcc-bugs-request@gcc.gnu.org?subject=unsubscribe>
List-Archive: <https://gcc.gnu.org/pipermail/gcc-bugs/>
List-Post: <mailto:gcc-bugs@gcc.gnu.org>
List-Help: <mailto:gcc-bugs-request@gcc.gnu.org?subject=help>
List-Subscribe: <https://gcc.gnu.org/mailman/listinfo/gcc-bugs>,
 <mailto:gcc-bugs-request@gcc.gnu.org?subject=subscribe>
X-List-Received-Date: Mon, 02 Aug 2021 09:14:07 -0000

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D24847

--- Comment #6 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Ivan Godard from comment #0)
> The second constructor is intended to catch the case: "foo<T, 5, A>(foo<T,
> 0, A>", i.e. to convert an instance of foo with second argument zero to a
> foo with any other second argument.

You can define that as:

explicit    foo(const foo<T, 0, x>&);

Or:

template<int N, typename =3D std::enable_if_t<N =3D=3D 0 && i !=3D 0>
explicit    foo(foo<T, N, x>);

Or in C++20:

explicit    foo(foo<T, 0, x>) requires (i !=3D 0);=