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Commit 06715e1c by Jonathan Wakely Committed by Jonathan Wakely
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PR libstdc++/90165 constrain variant(T&&) constructor 

Also refactor some constraints slightly to be more readable.

	PR libstdc++/90165
	* include/std/variant (variant::__not_self): New helper for the
	is_same_v<remove_cvref_t<T>, variant>==false constraints.
	(variant::__to_type_impl): Remove.
	(variant::__to_type): Add default argument to check pack size, instead
	of using __to_type_impl.
	(variant::__accepted_type): Add default argument using __not_self.
	(variant::__is_in_place_tag, variant::__not_in_place_tag): New helpers
	for variant(T&&) constructor constraint.
	(variant::variant(T&&)): Use __not_in_place_tag in constraints.
	Extract __accepted_type into a named template parameter for reuse in
	other constraints and in the exception specification.
	(variant::variant(in_place_type_t<T>, Args&&...))
	(variant::variant(in_place_type_t<T>, initializer_list<U>, Args&&...))
	(variant::variant(in_place_index_t<T>, Args&&...))
	(variant::variant(in_place_index_t<T>, initializer_list<U>, Args&&...))
	(variant::operator=T&&)): Remove redundant && from trait arguments.
	* testsuite/20_util/variant/compile.cc: Check variant(T&&) constructor
	isn't used for in_place_type or in_place_index arguments.

From-SVN: r270509
parent 82e8c3da
Showing with 64 additions and 27 deletions
libstdc++-v3/ChangeLog
2019-04-23 Jonathan Wakely <jwakely@redhat.com>
PR libstdc++/90165
* include/std/variant (variant::__not_self): New helper for the
is_same_v<remove_cvref_t<T>, variant>==false constraints.
(variant::__to_type_impl): Remove.
(variant::__to_type): Add default argument to check pack size, instead
of using __to_type_impl.
(variant::__accepted_type): Add default argument using __not_self.
(variant::__is_in_place_tag, variant::__not_in_place_tag): New helpers
for variant(T&&) constructor constraint.
(variant::variant(T&&)): Use __not_in_place_tag in constraints.
Extract __accepted_type into a named template parameter for reuse in
other constraints and in the exception specification.
(variant::variant(in_place_type_t<T>, Args&&...))
(variant::variant(in_place_type_t<T>, initializer_list<U>, Args&&...))
(variant::variant(in_place_index_t<T>, Args&&...))
(variant::variant(in_place_index_t<T>, initializer_list<U>, Args&&...))
(variant::operator=T&&)): Remove redundant && from trait arguments.
* testsuite/20_util/variant/compile.cc: Check variant(T&&) constructor
isn't used for in_place_type or in_place_index arguments.
* include/std/type_traits (unwrap_reference_t): Define for C++2a.
(unwrap_ref_decay): Remove inheritance from unwrap_reference.
* testsuite/20_util/unwrap_reference/1.cc: Adjust test to use alias.
......
libstdc++-v3/include/std/variant
......@@ -1285,6 +1285,10 @@ namespace __variant
variant<_Types...>>;
template<typename _Tp>
static constexpr bool __not_self
= !is_same_v<__remove_cvref_t<_Tp>, variant>;
template<typename _Tp>
static constexpr bool
__exactly_once = __detail::__variant::__exactly_once<_Tp, _Types...>;
......@@ -1292,17 +1296,10 @@ namespace __variant
static constexpr size_t __accepted_index =
__detail::__variant::__accepted_index<_Tp&&, variant>::value;
template<size_t _Np, bool = _Np < sizeof...(_Types)>
struct __to_type_impl;
template<size_t _Np>
struct __to_type_impl<_Np, true>
{ using type = variant_alternative_t<_Np, variant>; };
template<size_t _Np, typename = enable_if_t<(_Np < sizeof...(_Types))>>
using __to_type = variant_alternative_t<_Np, variant>;
template<size_t _Np>
using __to_type = typename __to_type_impl<_Np>::type;
template<typename _Tp>
template<typename _Tp, typename = enable_if_t<__not_self<_Tp>>>
using __accepted_type = __to_type<__accepted_index<_Tp>>;
template<typename _Tp>
......@@ -1311,6 +1308,17 @@ namespace __variant
using _Traits = __detail::__variant::_Traits<_Types...>;
template<typename _Tp>
struct __is_in_place_tag : false_type { };
template<typename _Tp>
struct __is_in_place_tag<in_place_type_t<_Tp>> : true_type { };
template<size_t _Np>
struct __is_in_place_tag<in_place_index_t<_Np>> : true_type { };
template<typename _Tp>
static constexpr bool __not_in_place_tag
= !__is_in_place_tag<__remove_cvref_t<_Tp>>::value;
public:
variant() = default;
variant(const variant& __rhs) = default;
......@@ -1320,20 +1328,21 @@ namespace __variant
~variant() = default;
template<typename _Tp,
typename = enable_if_t<!is_same_v<decay_t<_Tp>, variant>>,
typename = enable_if_t<(sizeof...(_Types)>0)>,
typename = enable_if_t<__exactly_once<__accepted_type<_Tp&&>>
&& is_constructible_v<__accepted_type<_Tp&&>, _Tp&&>>>
typename = enable_if_t<sizeof...(_Types) != 0>,
typename = enable_if_t<__not_in_place_tag<_Tp>>,
typename _Tj = __accepted_type<_Tp&&>,
typename = enable_if_t<__exactly_once<_Tj>
&& is_constructible_v<_Tj, _Tp>>>
constexpr
variant(_Tp&& __t)
noexcept(is_nothrow_constructible_v<__accepted_type<_Tp&&>, _Tp&&>)
noexcept(is_nothrow_constructible_v<_Tj, _Tp>)
: variant(in_place_index<__accepted_index<_Tp&&>>,
std::forward<_Tp>(__t))
{ }
template<typename _Tp, typename... _Args,
typename = enable_if_t<__exactly_once<_Tp>
&& is_constructible_v<_Tp, _Args&&...>>>
&& is_constructible_v<_Tp, _Args...>>>
constexpr explicit
variant(in_place_type_t<_Tp>, _Args&&... __args)
: variant(in_place_index<__index_of<_Tp>>,
......@@ -1342,8 +1351,8 @@ namespace __variant
template<typename _Tp, typename _Up, typename... _Args,
typename = enable_if_t<__exactly_once<_Tp>
&& is_constructible_v<
_Tp, initializer_list<_Up>&, _Args&&...>>>
&& is_constructible_v<_Tp,
initializer_list<_Up>&, _Args...>>>
constexpr explicit
variant(in_place_type_t<_Tp>, initializer_list<_Up> __il,
_Args&&... __args)
......@@ -1352,8 +1361,8 @@ namespace __variant
{ }
template<size_t _Np, typename... _Args,
typename = enable_if_t<
is_constructible_v<__to_type<_Np>, _Args&&...>>>
typename _Tp = __to_type<_Np>,
typename = enable_if_t<is_constructible_v<_Tp, _Args...>>>
constexpr explicit
variant(in_place_index_t<_Np>, _Args&&... __args)
: _Base(in_place_index<_Np>, std::forward<_Args>(__args)...),
......@@ -1361,8 +1370,10 @@ namespace __variant
{ }
template<size_t _Np, typename _Up, typename... _Args,
typename = enable_if_t<is_constructible_v<__to_type<_Np>,
initializer_list<_Up>&, _Args&&...>>>
typename _Tp = __to_type<_Np>,
typename = enable_if_t<is_constructible_v<_Tp,
initializer_list<_Up>&,
_Args...>>>
constexpr explicit
variant(in_place_index_t<_Np>, initializer_list<_Up> __il,
_Args&&... __args)
......@@ -1372,12 +1383,12 @@ namespace __variant
template<typename _Tp>
enable_if_t<__exactly_once<__accepted_type<_Tp&&>>
&& is_constructible_v<__accepted_type<_Tp&&>, _Tp&&>
&& is_assignable_v<__accepted_type<_Tp&&>&, _Tp&&>
&& !is_same_v<decay_t<_Tp>, variant>, variant&>
&& is_constructible_v<__accepted_type<_Tp&&>, _Tp>
&& is_assignable_v<__accepted_type<_Tp&&>&, _Tp>,
variant&>
operator=(_Tp&& __rhs)
noexcept(is_nothrow_assignable_v<__accepted_type<_Tp&&>&, _Tp&&>
&& is_nothrow_constructible_v<__accepted_type<_Tp&&>, _Tp&&>)
noexcept(is_nothrow_assignable_v<__accepted_type<_Tp&&>&, _Tp>
&& is_nothrow_constructible_v<__accepted_type<_Tp&&>, _Tp>)
{
constexpr auto __index = __accepted_index<_Tp&&>;
if (index() == __index)
......
libstdc++-v3/testsuite/20_util/variant/compile.cc
......@@ -144,10 +144,15 @@ void arbitrary_ctor()
static_assert(noexcept(variant<int, DefaultNoexcept>(DefaultNoexcept{})));
}
struct none { none() = delete; };
struct any { template <typename T> any(T&&) {} };
void in_place_index_ctor()
{
variant<string, string> a(in_place_index<0>, "a");
variant<string, string> b(in_place_index<1>, {'a'});
static_assert(!is_constructible_v<variant<none, any>, std::in_place_index_t<0>>, "PR libstdc++/90165");
}
void in_place_type_ctor()
......@@ -155,6 +160,7 @@ void in_place_type_ctor()
variant<int, string, int> a(in_place_type<string>, "a");
variant<int, string, int> b(in_place_type<string>, {'a'});
static_assert(!is_constructible_v<variant<string, string>, in_place_type_t<string>, const char*>);
static_assert(!is_constructible_v<variant<none, any>, std::in_place_type_t<none>>, "PR libstdc++/90165");
}
void dtor()
......
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