Deprecating arithmetic on std::atomic<void*>
Thu Apr 20 09:22:00 GMT 2017
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. â 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.
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