updated example. Demonstrate pass by reference

Author: facontidavide

examples/t08_additional_node_args.cpp

@@ -2,6 +2,19 @@
 
 using namespace BT;
 
+// To demonstrate how to pass arguments by reference, we
+// use a simple non-copyable object
+class NoCopyObj {
+public:
+  NoCopyObj(int val): _value(val) {}
+
+  NoCopyObj(const NoCopyObj& ) = delete;
+  NoCopyObj& operator =(const NoCopyObj& ) = delete;
+  int value() { return _value; }
+private:
+  int _value = 0;
+};
+
 /*
  * Sometimes, it is convenient to pass additional (static) arguments to a Node.
  * If these parameters are known at compilation time or at deployment-time
@@ -17,13 +30,14 @@ class Action_A : public SyncActionNode
 public:
   // additional arguments passed to the constructor
   Action_A(const std::string& name, const NodeConfig& config, int arg_int,
-           std::string arg_str) :
-    SyncActionNode(name, config), _arg1(arg_int), _arg2(arg_str)
+           std::string arg_str, NoCopyObj& nc) :
+    SyncActionNode(name, config), _arg1(arg_int), _arg2(arg_str), _nc(nc)
   {}
 
   NodeStatus tick() override
   {
-    std::cout << name() << ": " << _arg1 << " / " << _arg2 << std::endl;
+    std::cout << name() << ": " << _arg1 << " / "
+              << _arg2 << " / " << _nc.value() << std::endl;
     return NodeStatus::SUCCESS;
   }
   static PortsList providedPorts()
@@ -34,6 +48,7 @@ class Action_A : public SyncActionNode
 private:
   int _arg1;
   std::string _arg2;
+  NoCopyObj& _nc;
 };
 
 // Action_B implements an init(...) method that must be called once at the beginning.
@@ -83,8 +98,13 @@ int main()
 {
   BehaviorTreeFactory factory;
 
+  NoCopyObj non_copyable(88);
+
   // Passing the extra parameters to the constructor of Action_A
-  factory.registerNodeType<Action_A>("Action_A", 42, "hello world");
+  // note that if you want to pass an object by ref, instead of value
+  // (copy), you must use std::ref wrapper.
+  factory.registerNodeType<Action_A>("Action_A", 42, "hello world",
+                                     std::ref(non_copyable));
 
   // Action_B will require initialization
   factory.registerNodeType<Action_B>("Action_B");
@@ -103,7 +123,7 @@ int main()
   tree.tickWhileRunning();
 
   /* Expected output:
-        Action_A: 42 / hello world
+        Action_A: 42 / hello world / 88
         Action_B: 69 / interesting_value
   */
   return 0;