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Date: Sun, 13 Nov 2016 21:10:00 -0000
From: Jonathan Wakely <jwakely@redhat.com>
To: Ville Voutilainen <ville.voutilainen@gmail.com>
Cc: "gcc-patches@gcc.gnu.org" <gcc-patches@gcc.gnu.org>,        libstdc++ <libstdc++@gcc.gnu.org>
Subject: Re: [v3 PATCH] Implement P0504R0 (Revisiting in-place tag types for any/optional/variant).
Message-ID: <20161113211024.GJ21992@redhat.com>
References: <CAFk2RUYehjAUhYye_aEM1YFcfzmw+p-2Z=3ZYBaPiPBffNwCaQ@mail.gmail.com> <20161113210252.GH21992@redhat.com>
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On 13/11/16 21:02 +0000, Jonathan Wakely wrote:
>On 12/11/16 21:24 +0200, Ville Voutilainen wrote:
>>+  inline in_place_t in_place{};
>>+
>>+  template<typename _Tp> struct in_place_type_t
>>+  {
>>+    explicit in_place_type_t() = default;
>>+  };
>>+
>>+  template<typename _Tp>
>>+    in_place_type_t<_Tp> in_place_type{};
>>+
>>+  template<size_t _Idx> struct in_place_index_t
>>+  {
>>+    explicit in_place_index_t() = default;
>>+  };
>>+
>>+  template<size_t _Idx>
>>+    in_place_index_t<_Idx> in_place_index{};
>
>I was told there's a Core issue that says these are not actually
>inline variables unless they say "inline". Not sure which issue that
>is, but G++ does the right thing and makes them globally unique,
>rather than having internal linkage.
>
>(At LWG's request P0504R0 marked them inline just to be safe.)
>
>OK for trunk, thanks.

Oh, they aren't actually constexpr in your patch, so non-const, and so
don't get internal linkage. But they *should* be constexpr, please add
that to all three, and add inline to the two variable templates.