✨ add enable_if trait

include/zll/meta/enable_if.hpp

@@ -0,0 +1,24 @@
+/*
+ * 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_ENABLEIF_HPP
+#define ZLL_META_ENABLEIF_HPP
+
+namespace zll {
+namespace meta {
+
+template <bool, typename = void>
+struct enable_if {};
+
+template <typename T>
+struct enable_if<true, T> {
+    typedef T type;
+};
+
+}  // namespace meta
+}  // namespace zll
+
+#endif  // ZLL_META_ENABLEIF_HPP

include/zll/type_traits.hpp

@@ -7,6 +7,8 @@
 #ifndef ZLL_TYPETRAITS_HPP
 #define ZLL_TYPETRAITS_HPP
 
+#include "zll/meta/enable_if.hpp"
+
 #include "zll/meta/is_pointer.hpp"
 #include "zll/meta/is_same.hpp"
 

tests/unit_tests/meson.build

@@ -1,5 +1,6 @@
 
 unit_tests_srcs = [
+    'meta/enable_if_tests.cpp',
     'meta/integral_constant_tests.cpp',
     'meta/is_pointer_tests.cpp',
     'meta/is_same_tests.cpp',

tests/unit_tests/meta/enable_if_tests.cpp

@@ -0,0 +1,36 @@
+/*
+ * 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/enable_if.hpp"
+#include "zll/meta/is_same.hpp"
+#include "zll/meta/is_pointer.hpp"
+
+#include <utest.h>
+
+namespace test_types {
+enum test_values { f = 0, i, p };
+}
+
+template <typename T>
+typename zll::meta::enable_if<zll::meta::is_same<T, int>::value, test_types::test_values>::type test_function() {
+    return test_types::i;
+}
+
+template <typename T>
+typename zll::meta::enable_if<zll::meta::is_same<T, float>::value, test_types::test_values>::type test_function() {
+    return test_types::f;
+}
+
+template <typename T>
+typename zll::meta::enable_if<zll::meta::is_pointer<T>::value, test_types::test_values>::type test_function() {
+    return test_types::p;
+}
+
+UTEST(meta_enable_if, sfinae) {
+    ASSERT_EQ(test_function<int>(), test_types::i);
+    ASSERT_EQ(test_function<float>(), test_types::f);
+    ASSERT_EQ(test_function<int*>(), test_types::p);
+}