examples -> example

example/custom_rtti.cpp

@@ -0,0 +1,110 @@
+// 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)
+
+#ifdef _MSC_VER
+#pragma warning(disable : 4312)
+#endif
+
+struct Animal {
+    Animal(unsigned type) : type(type) {
+    }
+
+    virtual ~Animal() = default;
+
+    unsigned type;
+    static constexpr unsigned static_type = 1;
+};
+
+struct Cat : Animal {
+    Cat() : Animal(static_type) {
+    }
+
+    static constexpr unsigned static_type = 2;
+};
+
+struct Dog : Animal {
+    Dog() : Animal(static_type) {
+    }
+
+    static constexpr unsigned static_type = 3;
+};
+
+#include <boost/openmethod/registry.hpp>
+#include <boost/openmethod/policies/vptr_vector.hpp>
+
+// tag::facet[]
+namespace bom = boost::openmethod;
+
+struct custom_rtti : bom::policies::rtti {
+    template<class Registry>
+    struct fn : bom::policies::rtti::fn<Registry> {
+        template<class T>
+        static constexpr bool is_polymorphic = std::is_base_of_v<Animal, T>;
+
+        template<typename T>
+        static auto static_type() -> bom::type_id {
+            if constexpr (is_polymorphic<T>) {
+                return reinterpret_cast<bom::type_id>(T::static_type);
+            } else {
+                return nullptr;
+            }
+        }
+
+        template<typename T>
+        static auto dynamic_type(const T& obj) -> bom::type_id {
+            if constexpr (is_polymorphic<T>) {
+                return reinterpret_cast<bom::type_id>(obj.type);
+            } else {
+                return nullptr;
+            }
+        }
+    };
+};
+// end::facet[]
+
+// tag::policy[]
+struct custom_policy : bom::registry<custom_rtti, bom::policies::vptr_vector> {
+};
+
+#define BOOST_OPENMETHOD_DEFAULT_REGISTRY custom_policy
+// end::policy[]
+
+// tag::example[]
+#include <iostream>
+
+#include <boost/openmethod.hpp>
+#include <boost/openmethod/compiler.hpp>
+
+using boost::openmethod::virtual_ptr;
+
+BOOST_OPENMETHOD(poke, (std::ostream&, virtual_ptr<Animal>), void);
+
+BOOST_OPENMETHOD_OVERRIDE(
+    poke, (std::ostream & os, virtual_ptr<Cat> /*cat*/), void) {
+    os << "hiss";
+}
+
+BOOST_OPENMETHOD_OVERRIDE(
+    poke, (std::ostream & os, virtual_ptr<Dog> /*dog*/), void) {
+    os << "bark";
+}
+
+BOOST_OPENMETHOD_CLASSES(Animal, Cat, Dog);
+
+auto main() -> int {
+    boost::openmethod::initialize();
+
+    std::unique_ptr<Animal> a(new Cat);
+    std::unique_ptr<Animal> b(new Dog);
+
+    poke(std::cout, *a); // prints "hiss"
+    std::cout << "\n";
+
+    poke(std::cout, *b); // prints "bark"
+    std::cout << "\n";
+
+    return 0;
+}
+// end::example[]