tuple_for_each(): Call visitor from start to end, not in reverse.

The test now passes.
murraycu · Mar 2, 2016 · 3de113f · 3de113f
1 parent 03a5727
commit 3de113f
Showing 1 changed file with 26 additions and 5 deletions.
diff --git a/tuple-utils/tuple_for_each.h b/tuple-utils/tuple_for_each.h
@@ -23,32 +23,53 @@ namespace tupleutils {
 
 namespace detail {
 
-template <template <typename> class T_visitor, std::size_t index,
+template <template <typename> class T_visitor, std::size_t size_from_index,
   typename... T_extras>
 struct tuple_for_each_impl {
   template <typename T>
   static void
   tuple_for_each(T&& t, T_extras&&... extras) {
+    //We use std::decay_t<> because tuple_size is not defined for references.
+    constexpr auto size = std::tuple_size<std::decay_t<T>>::value;
+    static_assert(size > 1, "size must be more than 0.");
+
+    constexpr auto index = size - size_from_index;
+    static_assert(index >= 0, "unexpected index.");
+
     using element_type = typename std::tuple_element<index, std::decay_t<T>>::type;
     T_visitor<element_type>::visit(std::get<index>(t), std::forward<T_extras>(extras)...);
 
-    tuple_for_each_impl<T_visitor, index - 1, T_extras...>::tuple_for_each(
+    tuple_for_each_impl<T_visitor, size_from_index - 1, T_extras...>::tuple_for_each(
       std::forward<T>(t), std::forward<T_extras>(extras)...);
   }
 };
 
 template <template <typename> class T_visitor, typename... T_extras>
-struct tuple_for_each_impl<T_visitor, 0, T_extras...> {
+struct tuple_for_each_impl<T_visitor, 1, T_extras...> {
   template <typename T>
   static void
   tuple_for_each(T&& t, T_extras&&... extras) {
-    constexpr std::size_t index = 0;
+    //We use std::decay_t<> because tuple_size is not defined for references.
+    constexpr auto size = std::tuple_size<std::decay_t<T>>::value;
+    static_assert(size > 0, "size must be more than 0.");
+
+    constexpr auto index = size - 1;
+    static_assert(index > 0, "unexpected index.");
 
     using element_type = typename std::tuple_element<index, std::decay_t<T>>::type;
     T_visitor<element_type>::visit(std::get<index>(std::forward<T>(t)), std::forward<T_extras>(extras)...);
   }
 };
 
+template <template <typename> class T_visitor, typename... T_extras>
+struct tuple_for_each_impl<T_visitor, 0, T_extras...> {
+  template <typename T>
+  static void
+  tuple_for_each(T&& /* t */, T_extras&&... /* extras */) {
+    //Do nothing because the tuple has no elements.
+  }
+};
+
 } // detail namespace
 
 
@@ -73,7 +94,7 @@ tuple_for_each(T&& t, T_extras&&... extras) {
     return;
   }
 
-  detail::tuple_for_each_impl<T_visitor, size - 1, T_extras...>::tuple_for_each(
+  detail::tuple_for_each_impl<T_visitor, size, T_extras...>::tuple_for_each(
     std::forward<T>(t), std::forward<T_extras>(extras)...);
 }