Index: include/algorithm
===================================================================
--- include/algorithm
+++ include/algorithm
@@ -1687,26 +1687,7 @@
 }
 
 // copy
-
 template <class _Iter>
-struct __libcpp_is_trivial_iterator
-{
-    static const bool value = is_pointer<_Iter>::value;
-};
-
-template <class _Iter>
-struct __libcpp_is_trivial_iterator<move_iterator<_Iter> >
-{
-    static const bool value = is_pointer<_Iter>::value;
-};
-
-template <class _Iter>
-struct __libcpp_is_trivial_iterator<__wrap_iter<_Iter> >
-{
-    static const bool value = is_pointer<_Iter>::value;
-};
-
-template <class _Iter>
 inline _LIBCPP_INLINE_VISIBILITY
 _Iter
 __unwrap_iter(_Iter __i)
Index: include/iterator
===================================================================
--- include/iterator
+++ include/iterator
@@ -437,6 +437,10 @@
 template <class _Tp>
 struct __is_random_access_iterator : public __has_iterator_category_convertible_to<_Tp, random_access_iterator_tag> {};
 
+template <class _Tp>
+struct __is_exactly_input_iterator 
+	: integral_constant<bool, is_same<typename iterator_traits<_Tp>::iterator_category, input_iterator_tag>::value> {};
+
 template<class _Category, class _Tp, class _Distance = ptrdiff_t,
          class _Pointer = _Tp*, class _Reference = _Tp&>
 struct _LIBCPP_TYPE_VIS_ONLY iterator
@@ -1404,6 +1408,23 @@
     return __x;
 }
 
+template <class _Iter>
+struct __libcpp_is_trivial_iterator
+	: public _LIBCPP_BOOL_CONSTANT(is_pointer<_Iter>::value) {};
+	
+template <class _Iter>
+struct __libcpp_is_trivial_iterator<move_iterator<_Iter> >
+	: public _LIBCPP_BOOL_CONSTANT(__libcpp_is_trivial_iterator<_Iter>::value) {};
+
+template <class _Iter>
+struct __libcpp_is_trivial_iterator<reverse_iterator<_Iter> >
+	: public _LIBCPP_BOOL_CONSTANT(__libcpp_is_trivial_iterator<_Iter>::value) {};
+
+template <class _Iter>
+struct __libcpp_is_trivial_iterator<__wrap_iter<_Iter> >
+	: public _LIBCPP_BOOL_CONSTANT(__libcpp_is_trivial_iterator<_Iter>::value) {};
+
+
 template <class _Tp, size_t _Np>
 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
 _Tp*
Index: include/string
===================================================================
--- include/string
+++ include/string
@@ -1201,6 +1201,24 @@
 #pragma warning( pop )
 #endif // _LIBCPP_MSVC
 
+#ifdef _LIBCPP_HAS_NO_NOEXCEPT
+struct __libcpp_string_gets_noexcept_iterator_impl : public _LIBCPP_BOOL_CONSTANT(false) {};
+#else
+template <class _Iter>
+struct __libcpp_string_gets_noexcept_iterator_impl : public _LIBCPP_BOOL_CONSTANT((
+	__is_forward_iterator<_Iter>::value && 
+// 	noexcept(declval<_Iter>().operator++()) && 
+// 	noexcept(++(declval<_Iter>())) && 
+	noexcept(declval<_Iter>() == declval<_Iter>()) && 
+	noexcept(*declval<_Iter>())
+)) {};
+#endif
+
+
+template <class _Iter>
+struct __libcpp_string_gets_noexcept_iterator
+	: public _LIBCPP_BOOL_CONSTANT(__libcpp_is_trivial_iterator<_Iter>::value || __libcpp_string_gets_noexcept_iterator_impl<_Iter>::value) {};
+
 #ifdef _LIBCPP_ABI_ALTERNATE_STRING_LAYOUT
 
 template <class _CharT, size_t = sizeof(_CharT)>
@@ -1535,15 +1553,16 @@
     template<class _InputIterator>
         typename enable_if
         <
-             __is_input_iterator  <_InputIterator>::value &&
-            !__is_forward_iterator<_InputIterator>::value,
+           __is_exactly_input_iterator<_InputIterator>::value
+                || !__libcpp_string_gets_noexcept_iterator<_InputIterator>::value,
             basic_string&
         >::type
         assign(_InputIterator __first, _InputIterator __last);
     template<class _ForwardIterator>
         typename enable_if
         <
-            __is_forward_iterator<_ForwardIterator>::value,
+            __is_forward_iterator<_ForwardIterator>::value
+                 && __libcpp_string_gets_noexcept_iterator<_ForwardIterator>::value,
             basic_string&
         >::type
         assign(_ForwardIterator __first, _ForwardIterator __last);
@@ -2494,15 +2513,15 @@
 template<class _InputIterator>
 typename enable_if
 <
-     __is_input_iterator  <_InputIterator>::value &&
-    !__is_forward_iterator<_InputIterator>::value,
+     __is_exactly_input_iterator <_InputIterator>::value
+          || !__libcpp_string_gets_noexcept_iterator<_InputIterator>::value,
     basic_string<_CharT, _Traits, _Allocator>&
 >::type
 basic_string<_CharT, _Traits, _Allocator>::assign(_InputIterator __first, _InputIterator __last)
 {
-    clear();
-    for (; __first != __last; ++__first)
-        push_back(*__first);
+	call_input();
+	basic_string temp(__first, __last);
+    this->swap(temp);
     return *this;
 }
 
@@ -2510,11 +2529,13 @@
 template<class _ForwardIterator>
 typename enable_if
 <
-    __is_forward_iterator<_ForwardIterator>::value,
+    __is_forward_iterator<_ForwardIterator>::value
+         && __libcpp_string_gets_noexcept_iterator<_ForwardIterator>::value,
     basic_string<_CharT, _Traits, _Allocator>&
 >::type
 basic_string<_CharT, _Traits, _Allocator>::assign(_ForwardIterator __first, _ForwardIterator __last)
 {
+	call_forward();
     size_type __n = static_cast<size_type>(_VSTD::distance(__first, __last));
     size_type __cap = capacity();
     if (__cap < __n)