add a small rtti experiment

.gitignore

@@ -17,3 +17,4 @@ casts
 classes
 lvalues
 bad_alloc
+rtti

CMakeLists.txt

@@ -17,3 +17,4 @@ add_executable(casts casts.cpp)
 add_executable(classes classes.cpp)
 add_executable(lvalues lvalues.cpp)
 add_executable(bad_alloc bad_alloc.cpp)
+add_executable(rtti rtti.cpp)

rtti.cpp

@@ -0,0 +1,79 @@
+#include <iostream>
+#include <stdexcept>
+#include <typeinfo>
+
+
+class Nail {
+  public:
+    Nail(float length)
+    : length(length) {};
+
+    float getLength() {
+      return length;
+    }
+
+  private:
+    float length;
+};
+
+
+class Tool {
+  public:
+    virtual void use() {
+      std::cout << "Just using some tool." << std::endl;
+    }
+};
+
+
+class Hammer : public Tool {
+  public:
+    virtual void use() {
+      std::cout << "Hammer time!" << std::endl;
+    }
+
+    void use(Nail nail) {
+      std::cout << "The nail is " << nail.getLength() << " cm long" << std::endl;
+    }
+};
+
+
+class SledgeHammer : public Hammer {
+  public:
+    void use(Nail nail __attribute__((unused))) {
+      throw std::runtime_error("Can't use a sledge hammer on nails!");
+    }
+};
+
+
+void useSomeTool(Tool &tool) {
+  // RTTI gives up the type of the derived class.
+  std::cout << "Look, it's a " << typeid(tool).name() << "!" << std::endl;
+
+  // XXX What about subclasses of Hammer?
+  if(typeid(tool) == typeid(Hammer)) {
+    std::cout << "Stop! ";
+  }
+  tool.use();
+
+  // Or dynamic_cast it and use it on a nail
+  // XXX How to use a reference here?
+  Hammer* h = dynamic_cast<Hammer*>(&tool);
+  if (h) {
+    Nail nail(10);
+    h->use(nail);
+  }
+}
+
+
+int main() {
+  Tool tool;
+  Hammer hammer;
+  SledgeHammer sledgehammer;
+
+  useSomeTool(tool);
+  useSomeTool(hammer);
+  useSomeTool(sledgehammer);
+}
+
+// XXX http://en.cppreference.com/w/cpp/language/typeid
+// XXX https://en.wikipedia.org/wiki/Dynamic_cast