From b6053e1ddcc7fa2dbcbda6c18dd844528bc28ce6 Mon Sep 17 00:00:00 2001
From: Tobias Zindl <zie.develop@gmail.com>
Date: Fri, 6 Oct 2023 18:47:36 +0200
Subject: [PATCH] :sparkles: add enable_if trait

---
 include/zll/meta/enable_if.hpp            | 24 +++++++++++++++
 include/zll/type_traits.hpp               |  2 ++
 tests/unit_tests/meson.build              |  1 +
 tests/unit_tests/meta/enable_if_tests.cpp | 36 +++++++++++++++++++++++
 4 files changed, 63 insertions(+)
 create mode 100644 include/zll/meta/enable_if.hpp
 create mode 100644 tests/unit_tests/meta/enable_if_tests.cpp

diff --git a/include/zll/meta/enable_if.hpp b/include/zll/meta/enable_if.hpp
new file mode 100644
index 0000000..0714cd4
--- /dev/null
+++ b/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
diff --git a/include/zll/type_traits.hpp b/include/zll/type_traits.hpp
index eeee223..e200975 100644
--- a/include/zll/type_traits.hpp
+++ b/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"
 
diff --git a/tests/unit_tests/meson.build b/tests/unit_tests/meson.build
index fcfe88b..cc1dc27 100644
--- a/tests/unit_tests/meson.build
+++ b/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',
diff --git a/tests/unit_tests/meta/enable_if_tests.cpp b/tests/unit_tests/meta/enable_if_tests.cpp
new file mode 100644
index 0000000..d81791c
--- /dev/null
+++ b/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);
+}