Extracted comparator function into insert caller

impls/btree.cpp

@@ -17,13 +17,11 @@ struct BinaryTree
 {
   T value;
   BinaryTree<T> *left, *right;
-  enum Order (*compare)(T, T);
-  BinaryTree(T val, BinaryTree<T> *l, BinaryTree<T> *r, enum Order (*cmp)(T, T))
+  BinaryTree(T val, BinaryTree<T> *l, BinaryTree<T> *r)
   {
     value   = val;
     left    = l;
     right   = r;
-    compare = cmp;
   }
 
   ~BinaryTree()
@@ -34,10 +32,13 @@ struct BinaryTree
 };
 
 template <typename T>
-BinaryTree<T> *insert(BinaryTree<T> *tree, T value)
+using comp_fn = enum Order (*)(T, T);
+
+template <typename T>
+BinaryTree<T> *insert(BinaryTree<T> *tree, T value, comp_fn<T> compare)
 {
   BinaryTree<T> **node = &tree;
-  switch (tree->compare(value, tree->value))
+  switch (compare(value, tree->value))
   {
   case LT:
     node = &tree->left;
@@ -47,8 +48,8 @@ BinaryTree<T> *insert(BinaryTree<T> *tree, T value)
     node = &tree->right;
     break;
   }
-  *node = *node ? insert(*node, value)
-                : new BinaryTree<T>(value, nullptr, nullptr, tree->compare);
+  *node = *node ? insert(*node, value, compare)
+                : new BinaryTree<T>(value, nullptr, nullptr);
   return tree;
 }
 
@@ -75,20 +76,18 @@ std::ostream &operator<<(std::ostream &ostream, const BinaryTree<T> *btree)
 {
   if (!btree)
     return ostream;
-  ostream << btree->value << "(";
+  ostream << "(" << btree->value;
   if (btree->left)
-    ostream << btree->left;
-  if (btree->left && btree->right)
-    ostream << ", ";
+    ostream << " " << btree->left;
   if (btree->right)
-    ostream << btree->right;
+    ostream << " " << btree->right;
   ostream << ")";
   return ostream;
 }
 
 int main(void)
 {
-  auto cmp = [](int x, int y)
+  comp_fn<int> cmp = [](int x, int y)
   {
     if (x < y)
       return LT;
@@ -97,10 +96,11 @@ int main(void)
     else
       return EQ;
   };
-  auto tree = new BinaryTree<int>(5, NULL, NULL, cmp);
+  auto tree = new BinaryTree<int>(5, NULL, NULL);
   for (int i = 0; i <= 5; ++i)
-    tree = insert(tree, i * 2);
+    tree = insert(tree, i * 2, cmp);
 
+  std::cout << tree << std::endl;
   leftRotate(&tree);
   std::cout << tree << std::endl;