add some classes experiment

.gitignore

@@ -14,3 +14,4 @@ accumulate
 object-lifetime
 shared_ptr
 casts
+classes

CMakeLists.txt

@@ -14,3 +14,4 @@ add_executable(accumulate accumulate.cpp)
 add_executable(object-lifetime object-lifetime.cpp)
 add_executable(shared_ptr shared_ptr.cpp)
 add_executable(casts casts.cpp)
+add_executable(classes classes.cpp)

classes.cpp

@@ -0,0 +1,41 @@
+#include <iostream>
+#include <vector>
+
+class Animal {
+  public:
+    // Note: using *virtual* does the difference here!
+    virtual void makeSound() {
+      std::cout << "<generic animal sound>" << std::endl;
+    }
+};
+
+class Cow : public Animal {
+  public:
+    void makeSound() {
+      std::cout << "Mooh." << std::endl;
+    }
+};
+
+class Cat : public Animal {
+  public:
+    void makeSound() {
+      std::cout << "Meow?" << std::endl;
+    }
+};
+
+int main() {
+  Cat cat;
+  Cow cow;
+
+  // Does nothing:
+  std::vector<Animal> animals = { cat, cow };
+  for (auto &a: animals) {
+    a.makeSound();
+  }
+
+  // Meow? Mooh.
+  std::vector<Animal*> animalptrs = { &cat, &cow };
+  for (auto &a: animalptrs) {
+    a->makeSound();
+  }
+}