Remove addtional parameters in function std::next() and std::prev()

[jasonliu]

Summary

Creating a function pointer with proper parameters pointing to std::next() or std::prev() should work.
This change moves the invented paramater for enable_if over to the return type to resolve this QoI issue.

[• Quuxplusone]

include/iterator

619

Might fix the spelling error in "BidirectionalIter" while you're here.

[EricWF]

Creating a function pointer with proper parameters pointing to std::next() or std::prev() should work.

Actually, according to the standard taking the address of a STL function is UB, and users should avoid doing it as much as possible since it's fundamentally non-portable.

However as a QoI change I think this is OK.

include/iterator

 typename iterator_traits<_InputIter>::difference_type
 distance(_InputIter __first, _InputIter __last)
 {
     return __distance(__first, __last, typename iterator_traits<_InputIter>::iterator_category());
 }
 
 template <class _InputIter>
 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14
+typename enable_if
+<
+    __is_input_iterator<_InputIter>::value, 
     _InputIter
+>::type
 next(_InputIter __x,
-     typename iterator_traits<_InputIter>::difference_type __n = 1,
-     typename enable_if<__is_input_iterator<_InputIter>::value>::type* = 0)
+     typename iterator_traits<_InputIter>::difference_type __n = 1)
 {
     _VSTD::advance(__x, __n);
     return __x;
 }
 
 template <class _BidiretionalIter>
 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14
+typename enable_if
+<
+    __is_bidirectional_iterator<_BidiretionalIter>::value, 
     _BidiretionalIter
+>::type
 prev(_BidiretionalIter __x,
-     typename iterator_traits<_BidiretionalIter>::difference_type __n = 1,
-     typename enable_if<__is_bidirectional_iterator<_BidiretionalIter>::value>::type* = 0)
+     typename iterator_traits<_BidiretionalIter>::difference_type __n = 1)
 {
     _VSTD::advance(__x, -__n);
     return __x;
 }
 
 
 template <class _Tp, class = void>
 struct __is_stashing_iterator : false_type {};

test/std/iterators/iterator.primitives/iterator.operations/next.pass.cpp

 
 #include "test_iterators.h"
 
 template <class It>
 void
 test(It i, typename std::iterator_traits<It>::difference_type n, It x)
 {
     assert(std::next(i, n) == x);
+
+    It (*next)(It, typename std::iterator_traits<It>::difference_type) = std::next;
+    assert(next(i, n) == x);
 }
 
 template <class It>
 void
 test(It i, It x)
 {
     assert(std::next(i) == x);
 }

test/std/iterators/iterator.primitives/iterator.operations/prev.pass.cpp

 
 #include "test_iterators.h"
 
 template <class It>
 void
 test(It i, typename std::iterator_traits<It>::difference_type n, It x)
 {
     assert(std::prev(i, n) == x);
+
+    It (*prev)(It, typename std::iterator_traits<It>::difference_type) = std::prev;
+    assert(prev(i, n) == x);
 }
 
 template <class It>
 void
 test(It i, It x)
 {
     assert(std::prev(i) == x);
 }