From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <jwakely@redhat.com>
Received: from us-smtp-delivery-124.mimecast.com
 (us-smtp-delivery-124.mimecast.com [216.205.24.124])
 by sourceware.org (Postfix) with ESMTP id E7FF3385780B
 for <libstdc++@gcc.gnu.org>; Wed, 12 May 2021 09:18:39 +0000 (GMT)
DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org E7FF3385780B
Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com
 [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id
 us-mta-437-V5vICUu7MDGc4XLDUwwhkQ-1; Wed, 12 May 2021 05:18:36 -0400
X-MC-Unique: V5vICUu7MDGc4XLDUwwhkQ-1
Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com
 [10.5.11.23])
 (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits))
 (No client certificate requested)
 by mimecast-mx01.redhat.com (Postfix) with ESMTPS id C67E01854E24;
 Wed, 12 May 2021 09:18:34 +0000 (UTC)
Received: from localhost (unknown [10.33.36.164])
 by smtp.corp.redhat.com (Postfix) with ESMTP id 5E8E42B59A;
 Wed, 12 May 2021 09:18:34 +0000 (UTC)
Date: Wed, 12 May 2021 10:18:33 +0100
From: Jonathan Wakely <jwakely@redhat.com>
To: Antony Polukhin <antoshkka@gmail.com>
Cc: libstdc++ <libstdc++@gcc.gnu.org>,
 gcc-patches List <gcc-patches@gcc.gnu.org>
Subject: Re: [PATCH] PR libstdc++/89728 diagnose some missuses of
 [locale.convenience] functions
Message-ID: <20210512091833.GA3008@redhat.com>
References: <CAKqmYPYf-Cp3Q68DuJwUzLNGZwS5b=tuzYoZk=dQLp=wFc5ESg@mail.gmail.com>
 <20210511200031.GZ3008@redhat.com>
MIME-Version: 1.0
In-Reply-To: <20210511200031.GZ3008@redhat.com>
X-Clacks-Overhead: GNU Terry Pratchett
X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23
X-Mimecast-Spam-Score: 0
X-Mimecast-Originator: redhat.com
Content-Type: text/plain; charset=us-ascii; format=flowed
Content-Disposition: inline
X-Spam-Status: No, score=-8.3 required=5.0 tests=BAYES_00, DKIMWL_WL_HIGH,
 DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, RCVD_IN_DNSWL_LOW,
 RCVD_IN_MSPIKE_H4, RCVD_IN_MSPIKE_WL, SPF_HELO_NONE, SPF_PASS,
 TXREP autolearn=unavailable autolearn_force=no version=3.4.2
X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on
 server2.sourceware.org
X-BeenThere: libstdc++@gcc.gnu.org
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: Libstdc++ mailing list <libstdc++.gcc.gnu.org>
List-Unsubscribe: <https://gcc.gnu.org/mailman/options/libstdc++>,
 <mailto:libstdc++-request@gcc.gnu.org?subject=unsubscribe>
List-Archive: <https://gcc.gnu.org/pipermail/libstdc++/>
List-Post: <mailto:libstdc++@gcc.gnu.org>
List-Help: <mailto:libstdc++-request@gcc.gnu.org?subject=help>
List-Subscribe: <https://gcc.gnu.org/mailman/listinfo/libstdc++>,
 <mailto:libstdc++-request@gcc.gnu.org?subject=subscribe>
X-List-Received-Date: Wed, 12 May 2021 09:18:41 -0000

On 11/05/21 21:00 +0100, Jonathan Wakely wrote:
>Alternatively, would it be even simpler to just define a partial
>specialization of ctype?
>
>template<typename _CharT, typename _Traits, typename _Alloc>
>  class ctype<basic_string<_CharT, _Traits, _Alloc> >
>  {
>#if __cplusplus >= 201103L
>      static_assert(something dependent,
>		    "std::basic_string used as a character type");
>#endif
>  private:
>    ctype();
>    ~ctype();
>  };
>
>This will work in C++98 too.

Or just leave it undefined, as libc++ seems to do according to your
comment in PR 89728:

error: implicit instantiation of undefined template 'std::__1::ctype<std::__1::basic_string<char> >'

Was your aim to have a static_assert that gives a more descriptive
error? We could leave it undefined in C++98 and have the static assert
for C++11 and up.