examples -> example

example/matrix.cpp

@@ -0,0 +1,148 @@
+// 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 <memory>
+#include <string>
+#include <typeinfo>
+
+#include <boost/openmethod.hpp>
+#include <boost/openmethod/compiler.hpp>
+#include <boost/openmethod/shared_ptr.hpp>
+
+using std::make_shared;
+using std::shared_ptr;
+using std::string;
+
+using boost::openmethod::make_shared_virtual;
+using boost::openmethod::shared_virtual_ptr;
+using boost::openmethod::virtual_ptr;
+
+struct matrix {
+    virtual ~matrix() {
+    }
+    virtual auto at(int row, int col) const -> double = 0;
+    // ...
+};
+
+struct dense_matrix : matrix {
+    virtual auto at(int /*row*/, int /*col*/) const -> double {
+        return 0;
+    }
+};
+
+struct diagonal_matrix : matrix {
+    virtual auto at(int /*row*/, int /*col*/) const -> double {
+        return 0;
+    }
+};
+
+BOOST_OPENMETHOD_CLASSES(matrix, dense_matrix, diagonal_matrix);
+
+BOOST_OPENMETHOD(to_json, (virtual_ptr<const matrix>), string);
+
+BOOST_OPENMETHOD_OVERRIDE(to_json, (virtual_ptr<const dense_matrix>), string) {
+    return "json for dense matrix...";
+}
+
+BOOST_OPENMETHOD_OVERRIDE(
+    to_json, (virtual_ptr<const diagonal_matrix>), string) {
+    return "json for diagonal matrix...";
+}
+
+// -----------------------------------------------------------------------------
+// matrix * matrix
+
+BOOST_OPENMETHOD(
+    times, (shared_virtual_ptr<const matrix>, shared_virtual_ptr<const matrix>),
+    shared_virtual_ptr<const matrix>);
+
+// catch-all matrix * matrix -> dense_matrix
+BOOST_OPENMETHOD_OVERRIDE(
+    times,
+    (shared_virtual_ptr<const matrix> /*a*/,
+     shared_virtual_ptr<const matrix> /*b*/),
+    shared_virtual_ptr<const dense_matrix>) {
+    return make_shared<const dense_matrix>();
+}
+
+// diagonal_matrix * diagonal_matrix -> diagonal_matrix
+BOOST_OPENMETHOD_OVERRIDE(
+    times,
+    (shared_virtual_ptr<const diagonal_matrix> /*a*/,
+     shared_virtual_ptr<const diagonal_matrix> /*b*/),
+    shared_virtual_ptr<const diagonal_matrix>) {
+    return make_shared_virtual<diagonal_matrix>();
+}
+
+inline auto operator*(shared_ptr<const matrix> a, shared_ptr<const matrix> b)
+    -> shared_virtual_ptr<const matrix> {
+    return times(a, b);
+}
+
+// -----------------------------------------------------------------------------
+// scalar * matrix
+
+BOOST_OPENMETHOD(
+    times, (double, shared_virtual_ptr<const matrix>),
+    shared_virtual_ptr<const matrix>);
+
+// catch-all matrix * scalar -> dense_matrix
+BOOST_OPENMETHOD_OVERRIDE(
+    times, (double /*a*/, shared_virtual_ptr<const matrix> /*b*/),
+    shared_virtual_ptr<const dense_matrix>) {
+    return make_shared_virtual<dense_matrix>();
+}
+
+BOOST_OPENMETHOD_OVERRIDE(
+    times, (double /*a*/, shared_virtual_ptr<const diagonal_matrix> /*b*/),
+    shared_virtual_ptr<const diagonal_matrix>) {
+    return make_shared_virtual<diagonal_matrix>();
+}
+
+// -----------------------------------------------------------------------------
+// matrix * scalar
+
+// just swap
+inline auto times(shared_virtual_ptr<const matrix> a, double b)
+    -> shared_virtual_ptr<const matrix> {
+    return times(b, a);
+}
+
+// -----------------------------------------------------------------------------
+// main
+
+#define check(expr)                                                            \
+    {                                                                          \
+        if (!(expr)) {                                                         \
+            cerr << #expr << " failed\n";                                      \
+        }                                                                      \
+    }
+
+auto main() -> int {
+    using std::cerr;
+    using std::cout;
+
+    boost::openmethod::initialize();
+
+    shared_ptr<const matrix> a = make_shared<dense_matrix>();
+    shared_ptr<const matrix> b = make_shared<diagonal_matrix>();
+    double s = 1;
+
+#ifdef BOOST_CLANG
+#pragma clang diagnostic ignored "-Wpotentially-evaluated-expression"
+#endif
+
+    check(typeid(*times(a, a)) == typeid(dense_matrix));
+    check(typeid(*times(a, b)) == typeid(dense_matrix));
+    check(typeid(*times(b, b)) == typeid(diagonal_matrix));
+    check(typeid(*times(s, a)) == typeid(dense_matrix));
+    check(typeid(*times(s, b)) == typeid(diagonal_matrix));
+
+    cout << to_json(*a) << "\n"; // json for dense matrix
+    cout << to_json(*b) << "\n"; // json for diagonal matrix
+
+    return 0;
+}