✨ add is_class trait

include/zll/meta/detail/constraints_type.hpp

@@ -0,0 +1,26 @@
+/*
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#ifndef ZLL_META_DETAIL_CONSTRAINTSTYPE_HPP
+#define ZLL_META_DETAIL_CONSTRAINTSTYPE_HPP
+
+namespace zll {
+namespace meta {
+namespace detail {
+
+template <typename T>
+struct larger_than {
+    T body[2];
+};
+
+typedef char no_type;
+typedef larger_than<no_type> yes_type;
+
+}  // namespace detail
+}  // namespace meta
+}  // namespace zll
+
+#endif  // ZLL_META_DETAIL_CONSTRAINTSTYPE_HPP

include/zll/meta/is_class.hpp

@@ -0,0 +1,39 @@
+/*
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#ifndef ZLL_META_ISCLASS_HPP
+#define ZLL_META_ISCLASS_HPP
+
+#include "zll/meta/enable_if.hpp"
+#include "zll/meta/integral_constant.hpp"
+#include "zll/meta/is_union.hpp"
+
+#include "zll/meta/detail/constraints_type.hpp"
+
+#include <cstdlib>
+
+namespace zll {
+namespace meta {
+
+namespace detail {
+
+struct is_class_helper {
+    template <typename T>
+    static typename enable_if<!(is_union<T>::value), yes_type>::type test(int T::*);
+
+    template <typename>
+    static no_type test(...);
+};
+
+}  // namespace detail
+
+template <typename T>
+struct is_class : bool_constant<(sizeof(detail::is_class_helper::test<T>(NULL)) == sizeof(detail::yes_type))> {};
+
+}  // namespace meta
+}  // namespace zll
+
+#endif  // ZLL_META_ISCLASS_HPP

tests/unit_tests/meson.build

@@ -2,6 +2,7 @@
 unit_tests_srcs = [
     'meta/enable_if_tests.cpp',
     'meta/integral_constant_tests.cpp',
+    'meta/is_class_tests.cpp',
     'meta/is_pointer_tests.cpp',
     'meta/is_same_tests.cpp',
     'meta/is_union_tests.cpp',

tests/unit_tests/meta/is_class_tests.cpp

@@ -0,0 +1,29 @@
+/*
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#include "zll/meta/is_class.hpp"
+
+#include <utest.h>
+
+struct test_struct {};
+class test_class {};
+
+union test_union {
+    class clazz {};
+};
+
+UTEST(meta_is_class, is_class) {
+    ASSERT_TRUE(zll::meta::is_class<test_class>::value);
+    ASSERT_TRUE(zll::meta::is_class<const test_class>::value);
+    ASSERT_TRUE(zll::meta::is_class<test_struct>::value);
+    ASSERT_TRUE(zll::meta::is_class<const test_struct>::value);
+
+    ASSERT_FALSE(zll::meta::is_class<test_struct*>::value);
+    ASSERT_FALSE(zll::meta::is_class<test_struct&>::value);
+    ASSERT_FALSE(zll::meta::is_class<test_union>::value);
+
+    ASSERT_TRUE(zll::meta::is_class<test_union::clazz>::value);
+}