[PATCH] Implement sane variant converting constructor (P0608R3)

[Jonathan Wakely]

	* include/std/variant (__overload_set): Remove.
	(_Arr): New helper.
	(_Build_FUN): New class template to define a single FUN overload,
	with specializations to prevent unwanted conversions, as per P0608R3.
	(_Build_FUNs): New class template to build an overload set of FUN.
	(_FUN_type): New alias template to perform overload resolution.
	(__accepted_type): Use integer_constant base for failure case. Use
	_FUN_type for successful case.
	(variant::__accepted_index): Use _Tp instead of _Tp&&.
	(variant::variant(_Tp&&)): Likewise.
	(variant::operator=(_Tp&&)): Likewise.

Tested powerpc64le-linux, committed to trunk.


-------------- next part --------------
A non-text attachment was scrubbed...
Name: patch.txt
Type: text/x-patch
Size: 8580 bytes
Desc: not available
URL: <http://gcc.gnu.org/pipermail/libstdc++/attachments/20190516/b53c0fd7/attachment.bin>