[v3 PATCH] Make the perfect-forwarding constructor of a two-element tuple sfinae away when the first argument is an allocator_arg.

[Ville Voutilainen]

On 19 December 2016 at 12:19, Jonathan Wakely <jwakely@redhat.com> wrote:
> On 18/12/16 13:33 +0200, Ville Voutilainen wrote:
>>
>> Andrzej Krzemienski pointed this out in a discussion related to any and
>> tags.
>> Our two-element tuple specialization doesn't make the perfect-forwarding
>> constructor and the allocator constructor properly mutually exclusive;
>> this
>> patch fixes that.
>>
>> Tested on Linux-x64, ok for trunk, gcc-6 and gcc-5?
>
>
> gcc-6-branch is frozen, so not there.

Not now, but when that branch reopens, presumably then?

> Should this be reported as a defect in the standard?

I don't think so, the standard doesn't specify a two-argument
specialization and the variadic
signature specified doesn't run into this problem. We can certainly
give the other vendors a heads-up
in case their implementations suffer from the same problem but the
standard itself is not defective.