adds expression tree node base class

Author: attwoodn

include/attwoodn/expression_tree.hpp

@@ -1,7 +1,5 @@
 #pragma once
 
-#include <iostream>
-
 namespace attwoodn::expression_tree {
 
     namespace op {
@@ -28,7 +26,21 @@ namespace attwoodn::expression_tree {
 
     }
 
-    static inline void say_hello() {
-        std::cout << "hello world!" << std::endl;
+    namespace tree {
+
+        /**
+         * The base class representing expression tree nodes
+        */
+        template<typename Obj>
+        class expression_tree_node_base {
+            public:
+                virtual ~expression_tree_node_base() {};
+                virtual bool evaluate(const Obj& obj) = 0;
+        };
+
+        class expression_tree_op_node;
+        class expression_tree_leaf_node;
+        
+
     }
 }

tests/test.cpp

@@ -1,7 +1,7 @@
-#include <attwoodn/expression_tree.hpp>
+#include <iostream>
 
 int main(int argc, char** argv) {
-    attwoodn::expression_tree::say_hello();
+    std::cout << "hello world!" << std::endl;
 
     return EXIT_SUCCESS;
 }