uvalue simplifying and usage example

manuals/meta_examples/uvalue_example.cpp

@@ -0,0 +1,83 @@
+/*******************************************************************************
+ * This file is part of the "https://github.com/blackmatov/meta.hpp"
+ * For conditions of distribution and use, see copyright notice in LICENSE.md
+ * Copyright (C) 2021-2022, by Matvey Cherevko (blackmatov@gmail.com)
+ ******************************************************************************/
+
+#include "../meta_manuals.hpp"
+
+namespace
+{
+    class shape {
+    public:
+        shape() = default;
+        shape(const shape&) = default;
+        virtual ~shape() = default;
+
+        virtual int get_area() const = 0;
+    };
+
+    class rectangle : public shape {
+    public:
+        explicit rectangle(int width, int height)
+        : width_{width}
+        , height_{height} {}
+
+        int get_width() const {
+            return width_;
+        }
+
+        int get_height() const {
+            return height_;
+        }
+
+        int get_area() const override {
+            return width_ * height_;
+        }
+    private:
+        int width_{};
+        int height_{};
+    };
+}
+
+TEST_CASE("meta/meta_examples/uvalue") {
+    namespace meta = meta_hpp;
+
+    // 'shape' class type registration
+    meta::class_<shape>()
+        .method_("get_area", &shape::get_area);
+
+    // 'rectangle' class type registration
+    meta::class_<rectangle>()
+        .base_<shape>()
+        .constructor_<int, int>()
+        .method_("get_width", &rectangle::get_width)
+        .method_("get_height", &rectangle::get_height);
+}
+
+TEST_CASE("meta/meta_examples/uvalue/usage") {
+    namespace meta = meta_hpp;
+
+    // the 'uvalue' class allows to store any copyable value inside
+    // it's widely used as return value types and as containers for storing metadata
+
+    meta::uvalue val{42};
+    CHECK(val.get_type() == meta::resolve_type<int>());
+
+    // we can get a reference to the stored data and even change it
+    val.get_as<int>() = 21;
+    CHECK(val.get_as<int>() == 21);
+
+    // uvalue can be copied, assigned, and moved
+    val = rectangle{10, 20};
+    CHECK(val.get_type() == meta::resolve_type<rectangle>());
+
+    // also, it supports upcasting for registered types
+    CHECK(val.get_as<shape>().get_area() == 200);
+
+    // upcasting is supported for pointers too
+    rectangle rect{3, 5};
+    val = &rect;
+    CHECK(val.get_as<shape*>()->get_area() == 15);
+    CHECK(val.get_type() == meta::resolve_type<rectangle*>());
+}