This is the mail archive of the
mailing list for the libstdc++ project.
Re: Deprecating arithmetic on std::atomic<void*>
- From: Jonathan Wakely <jwakely at redhat dot com>
- To: Florian Weimer <fweimer at redhat dot com>
- Cc: gcc at gcc dot gnu dot org, libstdc++ at gcc dot gnu dot org
- Date: Thu, 20 Apr 2017 10:22:14 +0100
- Subject: Re: Deprecating arithmetic on std::atomic<void*>
- Authentication-results: sourceware.org; auth=none
- Authentication-results: ext-mx04.extmail.prod.ext.phx2.redhat.com; dmarc=none (p=none dis=none) header.from=redhat.com
- Authentication-results: ext-mx04.extmail.prod.ext.phx2.redhat.com; spf=pass smtp.mailfrom=jwakely at redhat dot com
- Dkim-filter: OpenDKIM Filter v2.11.0 mx1.redhat.com 97B3D8B11B
- Dmarc-filter: OpenDMARC Filter v1.3.2 mx1.redhat.com 97B3D8B11B
- References: <20170419170736.GY3412@redhat.com> <email@example.com> <20170420091809.GA3412@redhat.com>
On 20/04/17 10:18 +0100, Jonathan Wakely wrote:
On 20/04/17 08:19 +0200, Florian Weimer wrote:
On 04/19/2017 07:07 PM, Jonathan Wakely wrote:
I know it's a bit late, but I'd like to propose deprecating the
libstdc++ extension that allows arithmetic on std::atomic<void*>.
Currently we make it behave like arithmetic on void*, which is also a
GNU extension (https://gcc.gnu.org/onlinedocs/gcc/Pointer-Arith.html).
We also allow arithmetic on types such as std::atomic<void(*)()> which
is probably not useful (PR 69769).
Why is it acceptable to have the extension for built-in types, but
not for library types wrapping them? Why be inconsistent about
C++17 [atomic.types.pointer] paragraph 4 says:
Requires: T shall be an object type, otherwise the program is
ill-formed. [Note: Pointer arithmetic on void* or function pointers
is ill-formed. — end note]
That doesn't give us any leeway to support it.
I suppose we could support it without -Wpedantic, although there's no
way for the library to know if the front-end is being pedantic or not.