1 files changed, 28 insertions, 28 deletions
diff --git a/libcxx/include/tuple b/libcxx/include/tuple
index 4c9ae42462e..32f43805ff7 100644
--- a/libcxx/include/tuple
+++ b/libcxx/include/tuple
@@ -986,39 +986,39 @@ get(const tuple<_Tp...>&& __t) _NOEXCEPT
 }
 
 #if _LIBCPP_STD_VER > 11
-// get by type
-template <typename _T1, size_t _Idx, typename... _Args>
-struct __find_exactly_one_t_helper;
-
-// -- find exactly one
-template <typename _T1, size_t _Idx, typename... _Args>
-struct __find_exactly_one_t_checker {
-    static constexpr size_t value = _Idx;
-//  Check the rest of the list to make sure there's only one
-    static_assert ( __find_exactly_one_t_helper<_T1, 0, _Args...>::value == -1, "type can only occur once in type list" );
-    };
 
+namespace __find_detail {
 
-template <typename _T1, size_t _Idx>
-struct __find_exactly_one_t_helper <_T1, _Idx> {
-    static constexpr size_t value = -1;
-    };
+static constexpr size_t __not_found = -1;
+static constexpr size_t __ambiguous = __not_found - 1;
 
-template <typename _T1, size_t _Idx, typename _Head, typename... _Args>
-struct __find_exactly_one_t_helper <_T1, _Idx, _Head, _Args...> {
-    static constexpr size_t value =
-        std::conditional<
-            std::is_same<_T1, _Head>::value,
-            __find_exactly_one_t_checker<_T1, _Idx,   _Args...>,
-            __find_exactly_one_t_helper <_T1, _Idx+1, _Args...>
-        >::type::value;
-    };
+inline _LIBCPP_INLINE_VISIBILITY
+constexpr size_t __find_idx_return(size_t __curr_i, size_t __res, bool __matches) {
+    return !__matches ? __res :
+        (__res == __not_found ? __curr_i : __ambiguous);
+}
+
+template <size_t _Nx>
+inline _LIBCPP_INLINE_VISIBILITY
+constexpr size_t __find_idx(size_t __i, const bool (&__matches)[_Nx]) {
+  return __i == _Nx ? __not_found :
+      __find_idx_return(__i, __find_idx(__i + 1, __matches), __matches[__i]);
+}
+
+template <class _T1, class ..._Args>
+struct __find_exactly_one_checked {
+  static constexpr bool __matches[] = {is_same<_T1, _Args>::value...};
+    static constexpr size_t value = __find_detail::__find_idx(0, __matches);
+    static_assert (value != __not_found, "type not found in type list" );
+    static_assert(value != __ambiguous,"type occurs more than once in type list");
+};
+
+} // namespace __find_detail;
 
 template <typename _T1, typename... _Args>
-struct __find_exactly_one_t {
-    static constexpr size_t value = __find_exactly_one_t_helper<_T1, 0, _Args...>::value;
-    static_assert ( value != -1, "type not found in type list" );
-    };
+struct __find_exactly_one_t
+    : public __find_detail::__find_exactly_one_checked<_T1, _Args...> {
+};
 
 template <class _T1, class... _Args>
 inline _LIBCPP_INLINE_VISIBILITY