[libc++] Declare std::tuple_element as struct instead of class

Similarly to https://reviews.llvm.org/rL350972, this revision changes
std::tuple_element from class to struct.

Fixes PR41331.
Thanks to Jan Wilken Dörrie for the patch.

Differential Revision: https://reviews.llvm.org/D60069

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@357411 91177308-0d34-0410-b5e6-96231b3b80d8

include/__tuple

@@ -53,26 +53,23 @@ template <class _Tp> struct _LIBCPP_TEMPLATE_VIS tuple_size<volatile _Tp> : publ
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS tuple_size<const volatile _Tp> : public tuple_size<_Tp> {};
 #endif
 
-template <size_t _Ip, class _Tp> class _LIBCPP_TEMPLATE_VIS tuple_element;
+template <size_t _Ip, class _Tp> struct _LIBCPP_TEMPLATE_VIS tuple_element;
 
 template <size_t _Ip, class _Tp>
-class _LIBCPP_TEMPLATE_VIS tuple_element<_Ip, const _Tp>
+struct _LIBCPP_TEMPLATE_VIS tuple_element<_Ip, const _Tp>
 {
-public:
     typedef typename add_const<typename tuple_element<_Ip, _Tp>::type>::type type;
 };
 
 template <size_t _Ip, class _Tp>
-class _LIBCPP_TEMPLATE_VIS tuple_element<_Ip, volatile _Tp>
+struct _LIBCPP_TEMPLATE_VIS tuple_element<_Ip, volatile _Tp>
 {
-public:
     typedef typename add_volatile<typename tuple_element<_Ip, _Tp>::type>::type type;
 };
 
 template <size_t _Ip, class _Tp>
-class _LIBCPP_TEMPLATE_VIS tuple_element<_Ip, const volatile _Tp>
+struct _LIBCPP_TEMPLATE_VIS tuple_element<_Ip, const volatile _Tp>
 {
-public:
     typedef typename add_cv<typename tuple_element<_Ip, _Tp>::type>::type type;
 };
 
@@ -281,9 +278,8 @@ using __type_pack_element = typename decltype(
 #endif
 
 template <size_t _Ip, class ..._Types>
-class _LIBCPP_TEMPLATE_VIS tuple_element<_Ip, __tuple_types<_Types...>>
+struct _LIBCPP_TEMPLATE_VIS tuple_element<_Ip, __tuple_types<_Types...>>
 {
-public:
     static_assert(_Ip < sizeof...(_Types), "tuple_element index out of range");
     typedef __type_pack_element<_Ip, _Types...> type;
 };
@@ -456,9 +452,8 @@ struct __tuple_assignable<_Tp, _Up, true, true>
 
 
 template <size_t _Ip, class ..._Tp>
-class _LIBCPP_TEMPLATE_VIS tuple_element<_Ip, tuple<_Tp...> >
+struct _LIBCPP_TEMPLATE_VIS tuple_element<_Ip, tuple<_Tp...> >
 {
-public:
     typedef typename tuple_element<_Ip, __tuple_types<_Tp...> >::type type;
 };
 

include/array

@@ -91,7 +91,7 @@ template <class T, size_t N >
   void swap(array<T,N>& x, array<T,N>& y) noexcept(noexcept(x.swap(y))); // C++17
 
 template <class T> struct tuple_size;
-template <size_t I, class T> class tuple_element;
+template <size_t I, class T> struct tuple_element;
 template <class T, size_t N> struct tuple_size<array<T, N>>;
 template <size_t I, class T, size_t N> struct tuple_element<I, array<T, N>>;
 template <size_t I, class T, size_t N> T& get(array<T, N>&) noexcept; // constexpr in C++14
@@ -433,10 +433,9 @@ struct _LIBCPP_TEMPLATE_VIS tuple_size<array<_Tp, _Size> >
     : public integral_constant<size_t, _Size> {};
 
 template <size_t _Ip, class _Tp, size_t _Size>
-class _LIBCPP_TEMPLATE_VIS tuple_element<_Ip, array<_Tp, _Size> >
+struct _LIBCPP_TEMPLATE_VIS tuple_element<_Ip, array<_Tp, _Size> >
 {
     static_assert(_Ip < _Size, "Index out of bounds in std::tuple_element<> (std::array)");
-public:
     typedef _Tp type;
 };
 

include/span

@@ -531,11 +531,10 @@ struct _LIBCPP_TEMPLATE_VIS tuple_size<span<_Tp, dynamic_extent>>; // declared b
 
 
 template <size_t _Ip, class _Tp, size_t _Size>
-class _LIBCPP_TEMPLATE_VIS tuple_element<_Ip, span<_Tp, _Size>>
+struct _LIBCPP_TEMPLATE_VIS tuple_element<_Ip, span<_Tp, _Size>>
 {
     static_assert( dynamic_extent != _Size, "std::tuple_element<> not supported for std::span<T, dynamic_extent>");
     static_assert(_Ip < _Size, "Index out of bounds in std::tuple_element<> (std::span)");
-public:
     typedef _Tp type;
 };
 

include/tuple

@@ -87,8 +87,8 @@ template <class T> struct tuple_size; // undefined
 template <class... T> struct tuple_size<tuple<T...>>;
 template <class T>
  inline constexpr size_t tuple_size_v = tuple_size<T>::value; // C++17
-template <size_t I, class T> class tuple_element; // undefined
-template <size_t I, class... T> class tuple_element<I, tuple<T...>>;
+template <size_t I, class T> struct tuple_element; // undefined
+template <size_t I, class... T> struct tuple_element<I, tuple<T...>>;
 template <size_t I, class T>
   using tuple_element_t = typename tuple_element <I, T>::type; // C++14
 

include/utility

@@ -103,7 +103,7 @@ struct piecewise_construct_t { };
 inline constexpr piecewise_construct_t piecewise_construct = piecewise_construct_t();
 
 template <class T> struct tuple_size;
-template <size_t I, class T> class tuple_element;
+template <size_t I, class T> struct tuple_element;
 
 template <class T1, class T2> struct tuple_size<pair<T1, T2> >;
 template <class T1, class T2> struct tuple_element<0, pair<T1, T2> >;
@@ -687,22 +687,20 @@ template <class _T1, class _T2>
     : public integral_constant<size_t, 2> {};
 
 template <size_t _Ip, class _T1, class _T2>
-class _LIBCPP_TEMPLATE_VIS tuple_element<_Ip, pair<_T1, _T2> >
+struct _LIBCPP_TEMPLATE_VIS tuple_element<_Ip, pair<_T1, _T2> >
 {
     static_assert(_Ip < 2, "Index out of bounds in std::tuple_element<std::pair<T1, T2>>");
 };
 
 template <class _T1, class _T2>
-class _LIBCPP_TEMPLATE_VIS tuple_element<0, pair<_T1, _T2> >
+struct _LIBCPP_TEMPLATE_VIS tuple_element<0, pair<_T1, _T2> >
 {
-public:
     typedef _T1 type;
 };
 
 template <class _T1, class _T2>
-class _LIBCPP_TEMPLATE_VIS tuple_element<1, pair<_T1, _T2> >
+struct _LIBCPP_TEMPLATE_VIS tuple_element<1, pair<_T1, _T2> >
 {
-public:
     typedef _T2 type;
 };
 

test/std/utilities/tuple/tuple.tuple/tuple.helper/tuple.include.array.pass.cpp

@@ -11,9 +11,8 @@
 // template <class... Types> class tuple;
 
 // template <size_t I, class... Types>
-// class tuple_element<I, tuple<Types...> >
+// struct tuple_element<I, tuple<Types...> >
 // {
-// public:
 //     typedef Ti type;
 // };
 //

test/std/utilities/tuple/tuple.tuple/tuple.helper/tuple_element.fail.cpp

@@ -11,9 +11,8 @@
 // template <class... Types> class tuple;
 
 // template <size_t I, class... Types>
-// class tuple_element<I, tuple<Types...> >
+// struct tuple_element<I, tuple<Types...> >
 // {
-// public:
 //     typedef Ti type;
 // };
 

test/std/utilities/tuple/tuple.tuple/tuple.helper/tuple_element.pass.cpp

@@ -11,9 +11,8 @@
 // template <class... Types> class tuple;
 
 // template <size_t I, class... Types>
-// class tuple_element<I, tuple<Types...> >
+// struct tuple_element<I, tuple<Types...> >
 // {
-// public:
 //     typedef Ti type;
 // };
 

test/std/utilities/tuple/tuple.tuple/tuple.helper/tuple_size_structured_bindings.pass.cpp

@@ -116,8 +116,7 @@ template <size_t N>
 int get(Test const&) { static_assert(N == 0, ""); return -1; }
 
 template <>
-class std::tuple_element<0, Test> {
-public:
+struct std::tuple_element<0, Test> {
   typedef int type;
 };