cleanup examples

develop/manuals/meta_examples/variable_example.cpp

@@ -0,0 +1,57 @@
+/*******************************************************************************
+ * 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) 2021-2024, by Matvey Cherevko (blackmatov@gmail.com)
+ ******************************************************************************/
+
+#include <meta.hpp/meta_all.hpp>
+
+#include <doctest/doctest.h>
+#include <fmt/core.h>
+
+namespace
+{
+    const double pi_v{3.1415926536};
+    const double sqrt2_v{1.4142135624};
+}
+
+TEST_CASE("meta/meta_examples/variable/usage") {
+    namespace meta = meta_hpp;
+
+    // 'constants' local scope declaration
+    const meta::scope constants_scope = meta::local_scope_("constants")
+        .variable_("pi_v", &pi_v)
+        .variable_("sqrt2_v", &sqrt2_v);
+
+    // finds the variable by name 'pi_v'
+    const meta::variable pi_variable = constants_scope.get_variable("pi_v");
+
+    // checks the type and data type of the found variable
+    CHECK(pi_variable.get_type() == meta::resolve_type<const double*>());
+    CHECK(pi_variable.get_type().get_data_type() == meta::resolve_type<double>());
+
+    // retrieves a variable value
+    const meta::uvalue pi_variable_value = pi_variable.get();
+
+    // checks the type of the retrieved value
+    CHECK(pi_variable_value.get_type() == meta::resolve_type<double>());
+
+    // checks the typed variable value
+    CHECK(pi_variable_value.as<double>() == doctest::Approx(3.14).epsilon(0.01));
+
+    // we can change variable values, but only non-const
+    CHECK_FALSE(pi_variable.try_set(6.0));
+
+    // prints all variables in the scope
+    fmt::print("* {}\n", constants_scope.get_name());
+    for ( const meta::variable& variable : constants_scope.get_variables() ) {
+        fmt::print("  - {} : {}\n",
+            variable.get_name(),
+            variable.get().as<double>());
+    }
+
+    // Output:
+    // * constants
+    //   - pi_v : 3.1415926536
+    //   - sqrt2_v : 1.4142135624
+}