examples -> example

example/virtual_func.cpp

@@ -0,0 +1,62 @@
+// Copyright (c) 2018-2025 Jean-Louis Leroy
+// Distributed under the Boost Software License, Version 1.0.
+// See accompanying file LICENSE_1_0.txt
+// or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+// clang-format off
+
+// tag::code[]
+
+#include <iostream>
+#include <memory>
+
+struct Animal {
+    Animal(std::string name) : name(name) {}
+    virtual ~Animal() = default;
+    virtual void poke(std::ostream&) = 0;
+    std::string name;
+};
+
+struct Cat : Animal {
+    using Animal::Animal;
+
+    void poke(std::ostream& os) override {
+        os << name << " hisses";
+    }
+};
+
+struct Dog : Animal {
+    using Animal::Animal;
+
+    void poke(std::ostream& os) override {
+        os << name << " barks";
+    }
+};
+
+struct Bulldog : Dog {
+    using Dog::Dog;
+
+    void poke(std::ostream& os) override {
+        Dog::poke(os);
+        os << " and bites back";
+    }
+};
+
+auto main() -> int {
+    std::unique_ptr<Animal> a(new Cat("Felix"));
+    std::unique_ptr<Animal> b(new Dog("Snoopy"));
+    std::unique_ptr<Animal> c(new Bulldog("Hector"));
+
+    a->poke(std::cout); // prints "Felix hisses"
+    std::cout << ".\n";
+
+    b->poke(std::cout); // prints "Snoopy barks"
+    std::cout << ".\n";
+
+    c->poke(std::cout); // prints "Hector barks and bites back"
+    std::cout << ".\n";
+
+    return 0;
+}
+
+// end::code[]