list: prefer use of queries over direct use of members

list/node.hpp

@@ -22,6 +22,60 @@ namespace cruft::list::node {
     };
 
 
+    /// Return a pointer to the successor node, or NULL if there isn't one.
+    template <typename ValueT>
+    compound<ValueT>*
+    next (compound<ValueT> *obj)
+    {
+        return obj->next;
+    }
+
+
+    /// Return a pointer to the successor node, or NULL if there isn't one.
+    template <typename ValueT>
+    compound<ValueT> const*
+    next (compound<ValueT> const *obj)
+    {
+        return obj->next;
+    }
+
+
+    /// Set the successor node and return a pointer to it.
+    template <typename ValueT>
+    compound<ValueT>*
+    next (compound<ValueT> *obj, compound<ValueT> *val)
+    {
+        return obj->next = val;
+    }
+
+
+    /// Clear the successor node and return a null pointer.
+    template <typename ValueT>
+    compound<ValueT>*
+    next (compound<ValueT> *obj, std::nullptr_t)
+    {
+        return obj->next = nullptr;
+    }
+
+
+    /// Return a reference to the node's data
+    template <typename ValueT>
+    ValueT&
+    data (compound<ValueT> *obj)
+    {
+        return obj->data;
+    }
+
+
+    /// Return a reference to the node's data
+    template <typename ValueT>
+    ValueT const&
+    data (compound<ValueT> const *obj)
+    {
+        return obj->data;
+    }
+
+
     /// A node that stores either a value, or a successor pointer. Not both.
     ///
     /// This is quite useful for node based pool allocators and similar.
@@ -31,21 +85,69 @@ namespace cruft::list::node {
     /// manage the lifetime of the `data` member and prevent copying of nodes
     /// with a live `data` member.
     template <typename ValueT>
-    union disjoint {
+    struct disjoint {
         using value_type = ValueT;
 
-        disjoint ()  { }
+        std::aligned_storage_t<sizeof (ValueT), alignof (ValueT)> bytes;
-
-        disjoint (disjoint const &rhs) { next = rhs.next; }
-        disjoint& operator= (disjoint const &rhs) { next = rhs.next; }
-
-        ~disjoint () { }
-
-        disjoint *next;
-        ValueT data;
     };
 
 
+    /// Return a pointer to the successor node, or NULL if there isn't one.
+    template <typename ValueT>
+    disjoint<ValueT>*
+    next (disjoint<ValueT> *obj)
+    {
+        disjoint<ValueT> *res;
+        memcpy (&res, &obj->bytes, sizeof (res));
+        return res;
+    }
+
+
+    /// Return a pointer to the successor node, or NULL if there isn't one.
+    template <typename ValueT>
+    disjoint<ValueT> const*
+    next (disjoint<ValueT> const *obj)
+    {
+        disjoint<ValueT> *res;
+        memcpy (&res, &obj->bytes, sizeof (res));
+        return res;
+    }
+
+
+    /// Set the successor node and return a pointer to it.
+    template <typename ValueT>
+    disjoint<ValueT>*
+    next (disjoint<ValueT> *obj, disjoint<ValueT> *val)
+    {
+        memcpy (&obj->bytes, &val, sizeof (val));
+        return val;
+    }
+
+
+    /// Clear the successor node and return a null pointer.
+    template <typename ValueT>
+    compound<ValueT>*
+    next (disjoint<ValueT> *obj, std::nullptr_t)
+    {
+        memset (&obj->bytes, 0, sizeof (ValueT*));
+        return nullptr;
+    }
+
+
+    /// Return a reference to the node's data
+    template <typename ValueT>
+    ValueT&
+    data (disjoint<ValueT> *obj)
+    {
+        static_assert (
+            sizeof (ValueT) >= sizeof (*obj),
+            "ValueT < disjoint* prevents array indexing of nodes"
+        );
+
+        return *reinterpret_cast<ValueT*> (&obj->bytes);
+    }
+
+
     /// A comparator object that returns the result of a supplied child
     /// comparator on the data members of two node pointers.
     template <typename ComparatorT>
@@ -75,6 +177,11 @@ namespace cruft::list::node {
     };
 
 
+    /// A comparator that returns true if the pointer to the first node is
+    /// less than the pointer to the second node.
+    ///
+    /// This is useful for sorting pool allocator nodes for further
+    /// processing.
     struct pointer_comparator {
         template <typename NodeT>
         constexpr bool

list/sort.hpp

@@ -27,7 +27,7 @@ namespace cruft::list {
 
         while (head) {
             ++count;
-            head = head->next;
+            head = next (head);
         }
 
         return count;
@@ -45,8 +45,8 @@ namespace cruft::list {
     {
         CHECK (head);
 
-        while (head->next)
+        while (next (head))
-            head = head->next;
+            head = next (head);
         return head;
     }
 
@@ -71,15 +71,15 @@ namespace cruft::list {
         // Pre-increment the fast node to trigger a preference for the earlier
         // of the middle nodes.
         auto slow = first;
-        auto fast = first->next;
+        auto fast = next (first);
 
-        while (fast != last->next) {
+        while (fast != next (last)) {
-            fast = fast->next;
+            fast = next (fast);
-            if (fast == last->next)
+            if (fast == next (last))
                 return slow;
 
-            fast = fast->next;
+            fast = next (fast);
-            slow = slow->next;
+            slow = next (slow);
         }
 
         return slow;
@@ -123,7 +123,7 @@ namespace cruft::list {
         auto extract = [&first, &middle, &cmp] () {
             auto &target = cmp (first, middle) ? first : middle;
             auto res = target;
-            target = target->next;
+            target = next (target);
             return res;
         };
 
@@ -132,17 +132,17 @@ namespace cruft::list {
 
         // Keep adding the lowest node to the new list until we exhaust one
         // or both of our sources.
-        while (first && middle && first != middle && middle != last->next) {
+        while (first && middle && first != middle && middle != next (last)) {
             auto target = extract ();
-            cursor->next = target;
+            next (cursor, target);
             cursor = target;
         }
 
         // Append the remaining data to the new list.
         if (first == middle || !first)
-            cursor->next = middle;
+            next (cursor, middle);
-        else if (middle == last->next || !middle)
+        else if (middle == next (last) || !middle)
-            cursor->next = first;
+            next (cursor, first);
 
         #if defined(COMPILER_CLANG)
         #pragma GCC diagnostic pop
@@ -171,8 +171,8 @@ namespace cruft::list {
             return first;
 
         auto a_end = ::cruft::list::midpoint (first, last);
-        auto middle = a_end->next;
+        auto middle = next (a_end);
-        a_end->next = nullptr;
+        next (a_end, nullptr);
 
         auto a = ::cruft::list::sort (first, a_end, cmp);
         auto b = ::cruft::list::sort (middle, last, cmp);
@@ -201,18 +201,18 @@ namespace cruft::list {
     is_sorted [[gnu::nonnull]] (
         NodeT const *head
     ) {
-        if (!head->next)
+        if (!next (head))
             return true;
 
         auto a = head;
-        auto b = head->next;
+        auto b = next (head);
 
         while (b) {
             if (b->data < a->data)
                 return false;
 
-            a = a->next;
+            a = next (a);
-            b = b->next;
+            b = next (b);
         }
 
         return true;