examples -> example

example/virtual_.cpp

@@ -0,0 +1,112 @@
+// 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/with_vptr.hpp>
+#include <boost/openmethod/compiler.hpp>
+
+using boost::openmethod::virtual_;
+
+// clang-format off
+
+namespace just_virtual {
+
+// tag::virtual_parameter[]
+struct Animal {
+    virtual ~Animal() = default;
+};
+
+struct Cat : Animal {};
+
+using boost::openmethod::virtual_;
+
+BOOST_OPENMETHOD(poke, (std::ostream&, virtual_<Animal&>), void);
+
+BOOST_OPENMETHOD_OVERRIDE(poke, (std::ostream & os, Cat& /*cat*/), void) {
+    os << "hiss";
+}
+
+BOOST_OPENMETHOD_CLASSES(Animal, Cat);
+// end::virtual_parameter[]
+} // namespace just_virtual
+
+namespace virtual_intrusive {
+
+// tag::virtual_intrusive[]
+
+class Animal {
+  protected:
+    boost::openmethod::vptr_type vptr;
+    friend auto boost_openmethod_vptr(const Animal& a, void*) {
+        return a.vptr;
+    }
+
+  public:
+    Animal() {
+        vptr = boost::openmethod::default_registry::static_vptr<Animal>;
+    }
+};
+
+class Cat : public Animal {
+  public:
+    Cat() {
+        vptr = boost::openmethod::default_registry::static_vptr<Cat>;
+    }
+};
+
+BOOST_OPENMETHOD(poke, (std::ostream&, virtual_<Animal&>), void);
+
+BOOST_OPENMETHOD_OVERRIDE(poke, (std::ostream & os, Cat& /*cat*/), void) {
+    os << "hiss\n";
+}
+
+BOOST_OPENMETHOD_CLASSES(Animal, Cat);
+// end::virtual_intrusive[]
+} // namespace virtual_intrusive
+
+namespace with_vptr {
+
+// tag::with_vptr[]
+
+#include <boost/openmethod/with_vptr.hpp>
+
+class Animal : public boost::openmethod::with_vptr<Animal> {
+};
+
+class Cat : public Animal, public boost::openmethod::with_vptr<Cat, Animal> {
+};
+
+BOOST_OPENMETHOD(poke, (std::ostream&, virtual_<Animal&>), void);
+
+BOOST_OPENMETHOD_OVERRIDE(poke, (std::ostream & os, Cat& /*cat*/), void) {
+    os << "hiss\n";
+}
+// end::with_vptr[]
+
+} // namespace with_vptr
+
+auto main() -> int {
+    boost::openmethod::initialize();
+
+    {
+        using namespace just_virtual;
+        Cat cat;
+        poke(std::cout, cat); // hiss
+    }
+
+    {
+        using namespace virtual_intrusive;
+        Cat cat;
+        poke(std::cout, cat); // hiss
+    }
+
+    {
+        using namespace with_vptr;
+        Cat cat;
+        poke(std::cout, cat); // hiss
+    }
+}