examples -> example

example/virtual_ptr.cpp

@@ -0,0 +1,73 @@
+// 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)
+
+#include <iostream>
+#include <boost/openmethod.hpp>
+#include <boost/openmethod/compiler.hpp>
+
+using boost::openmethod::virtual_ptr;
+
+struct Animal {
+    virtual ~Animal() = default;
+};
+
+struct Cat : Animal {};
+
+struct Dog : Animal {};
+
+BOOST_OPENMETHOD_CLASSES(Animal, Cat, Dog);
+
+BOOST_OPENMETHOD(yell, (std::ostream&, virtual_ptr<Animal>), void);
+
+BOOST_OPENMETHOD_OVERRIDE(
+    yell, (std::ostream & os, virtual_ptr<Cat> /*cat*/), void) {
+    os << "hiss";
+}
+
+BOOST_OPENMETHOD_OVERRIDE(
+    yell, (std::ostream & os, virtual_ptr<Dog> /*dog*/), void) {
+    os << "bark";
+}
+
+BOOST_OPENMETHOD(
+    encounter, (std::ostream&, virtual_ptr<Animal>, virtual_ptr<Animal>), void);
+
+BOOST_OPENMETHOD_OVERRIDE(
+    encounter,
+    (std::ostream & os, virtual_ptr<Dog> dog, virtual_ptr<Cat> /*cat*/), void) {
+    yell(os, dog);
+    os << " and chase";
+}
+
+BOOST_OPENMETHOD_OVERRIDE(
+    encounter,
+    (std::ostream & os, virtual_ptr<Cat> cat, virtual_ptr<Dog> /*dog*/), void) {
+    yell(os, cat);
+    os << " and run";
+}
+
+auto main() -> int {
+    boost::openmethod::initialize();
+
+    std::unique_ptr<Animal> a(new Cat);
+    std::unique_ptr<Animal> b(new Dog);
+
+    encounter(std::cout, *a, *b); // prints "hiss and run"
+    std::cout << "\n";
+
+    encounter(std::cout, *b, *a); // prints "bark and chase"
+    std::cout << "\n";
+
+    return 0;
+}
+
+void call_yell(std::ostream& os, virtual_ptr<Animal> a) {
+    yell(os, a);
+}
+
+void call_encounter(
+    std::ostream& os, virtual_ptr<Animal> a, virtual_ptr<Animal> b) {
+    encounter(os, a, b);
+}