Experimental support for a meaningful __is_swappable<T>::value. This does not appear to be strictly needed for correct functioning of the library. If it causes any problems, I'd rather pull it sooner rather than later.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@132421 91177308-0d34-0410-b5e6-96231b3b80d8

include/array

@@ -270,7 +270,11 @@ operator>=(const array<_Tp, _Size>& __x, const array<_Tp, _Size>& __y)
 
 template <class _Tp, size_t _Size>
 _LIBCPP_INLINE_VISIBILITY inline
-void
+typename enable_if
+<
+    __is_swappable<_Tp>::value,
+    void
+>::type
 swap(const array<_Tp, _Size>& __x, const array<_Tp, _Size>& __y)
                                   _NOEXCEPT_(__is_nothrow_swappable<_Tp>::value)
 {

include/tuple

@@ -587,7 +587,11 @@ public:
 
 template <class ..._Tp>
 inline _LIBCPP_INLINE_VISIBILITY
-void
+typename enable_if
+<
+    __all<__is_swappable<_Tp>::value...>::value,
+    void
+>::type
 swap(tuple<_Tp...>& __t, tuple<_Tp...>& __u)
                  _NOEXCEPT_(__all<__is_nothrow_swappable<_Tp>::value...>::value)
     {__t.swap(__u);}

include/utility

@@ -377,7 +377,12 @@ operator<=(const pair<_T1,_T2>& __x, const pair<_T1,_T2>& __y)
 
 template <class _T1, class _T2>
 inline _LIBCPP_INLINE_VISIBILITY
-void
+typename enable_if
+<
+    __is_swappable<_T1>::value &&
+    __is_swappable<_T2>::value,
+    void
+>::type
 swap(pair<_T1, _T2>& __x, pair<_T1, _T2>& __y)
                      _NOEXCEPT_((__is_nothrow_swappable<_T1>::value &&
                                  __is_nothrow_swappable<_T2>::value))