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 E9ADC386EC04; Thu, 30 Jun 2022 11:11:38 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org E9ADC386EC04
From: "redi at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/100157] Support `__type_pack_element` like Clang
Date: Thu, 30 Jun 2022 11:11:38 +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: 12.0
X-Bugzilla-Keywords: 
X-Bugzilla-Severity: enhancement
X-Bugzilla-Who: redi at gcc dot gnu.org
X-Bugzilla-Status: ASSIGNED
X-Bugzilla-Resolution: 
X-Bugzilla-Priority: P3
X-Bugzilla-Assigned-To: redi at gcc dot gnu.org
X-Bugzilla-Target-Milestone: 13.0
X-Bugzilla-Flags: 
X-Bugzilla-Changed-Fields: 
Message-ID: <bug-100157-4-enjTfkF1AT@http.gcc.gnu.org/bugzilla/>
In-Reply-To: <bug-100157-4@http.gcc.gnu.org/bugzilla/>
References: <bug-100157-4@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: Thu, 30 Jun 2022 11:11:39 -0000

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D100157

--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to m.cencora from comment #2)
> Please consider also adding a builtin for fetching index of type in type
> list.

I am already considering it and it's one of the reasons I don't like the na=
me
"type pack element". That name isn't easily extensible to the reverse case.

I would prefer a pair of similar names involving "type at index" and "index=
 of
type" or something like that. Or "index to type" and "tpe to index".

> While there are some easy implementations (like following), they are still
> not very performant.

The uses in the standard library also require an error if the type occurs m=
ore
than once, which yours doesn't check. I intend to add a built-in that suppo=
rts
both cases with a boolean flag to say whether to fail if the type is repeat=
ed.

FWIW I think __find_uniq_type_in_pack() in libstdc++'s <bits/utility.h> sca=
les
better than yours (and checks for uniqueness).=