Moved child pointers to OperatorNode class

* access was restricted by declaring them private and offering member methods such as "hasChildren"
* only OperatorNode instances have children, there is no reason for wasting space by keeping empty pointers around in all other instances
* this enabled the removal of all nullptr comparisons from tree construction
* changed "Tree::addNode" factory method template to return a pointer to the type of the constructed node instance instead of a plain node pointer

1 files changed, 13 insertions, 8 deletions

diff --git a/src/nodes.h b/src/nodes.h
index 9559722..95bf772 100644
--- a/src/nodes.h
+++ b/src/nodes.h
@@ -13,11 +13,10 @@ class Node {
 	public:
 		virtual ~Node() {};
 
-		virtual double solve()      const = 0;
-		virtual std::string print() const = 0;
-
-		Node* leftChild;
-		Node* rightChild;
+		virtual double solve()              const = 0;
+		virtual std::string print()         const = 0;
+		virtual bool hasChildren()          const;
+		virtual bool isParentOf(Node*const) const;
 
 };
 
@@ -25,15 +24,21 @@ class OperatorNode: public Node {
 	public:
 		explicit OperatorNode(TokenType);
 
-		TokenType token() const;
+		virtual double solve()              const;
+		virtual std::string print()         const;
+		virtual bool hasChildren()          const;
+		virtual bool isParentOf(Node*const) const;
 
-		virtual double solve()      const;
-		virtual std::string print() const;
+		TokenType token() const;
 
+		void setChildren(Node*const, Node*const);
 
 	private:
 		const TokenType operator_;
 
+		Node* right_;
+		Node* left_;
+
 };
 
 class OperandNode: public Node {