[v3 PATCH] Implement P0504R0 (Revisiting in-place tag types for any/optional/variant).

[Jonathan Wakely]

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.