From 56bfb9804c75ce1625517373148e9af11b6b7442 Mon Sep 17 00:00:00 2001
From: wmayer <wmayer@users.sourceforge.net>
Date: Sat, 8 Jan 2022 15:48:40 +0100
Subject: [PATCH] Base: [skip ci] support bitmask operations for enums

---
 src/Base/Bitmask.h      | 97 +++++++++++++++++++++++++++++++++++++++++
 src/Base/CMakeLists.txt |  1 +
 2 files changed, 98 insertions(+)
 create mode 100644 src/Base/Bitmask.h

diff --git a/src/Base/Bitmask.h b/src/Base/Bitmask.h
new file mode 100644
index 0000000000..d4732ca418
--- /dev/null
+++ b/src/Base/Bitmask.h
@@ -0,0 +1,97 @@
+/***************************************************************************
+ *   Copyright (c) 2022 Werner Mayer <wmayer[at]users.sourceforge.net>     *
+ *                                                                         *
+ *   This file is part of the FreeCAD CAx development system.              *
+ *                                                                         *
+ *   This library is free software; you can redistribute it and/or         *
+ *   modify it under the terms of the GNU Library General Public           *
+ *   License as published by the Free Software Foundation; either          *
+ *   version 2 of the License, or (at your option) any later version.      *
+ *                                                                         *
+ *   This library  is distributed in the hope that it will be useful,      *
+ *   but WITHOUT ANY WARRANTY; without even the implied warranty of        *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the         *
+ *   GNU Library General Public License for more details.                  *
+ *                                                                         *
+ *   You should have received a copy of the GNU Library General Public     *
+ *   License along with this library; see the file COPYING.LIB. If not,    *
+ *   write to the Free Software Foundation, Inc., 51 Franklin Street,      *
+ *   Fifth Floor, Boston, MA  02110-1301, USA                              *
+ *                                                                         *
+ ***************************************************************************/
+
+#include <type_traits>
+
+/*!
+ Using enum classes as type-safe bitmasks.
+ @code
+ enum class Color {
+   Red   = 1 << 0,
+   Green = 1 << 1,
+   Blue  = 1 << 2
+ };
+ ENABLE_BITMASK_OPERATORS(Color)
+
+ Color yellow = Color::Red | Color::Green;
+ @endcode
+*/
+
+// Based on https://stackoverflow.com/questions/1448396/how-to-use-enums-as-flags-in-c
+template<class T = void> struct enum_traits {};
+
+template<> struct enum_traits<void> {
+    struct _allow_bitops {
+        static constexpr bool allow_bitops = true;
+    };
+    using allow_bitops = _allow_bitops;
+
+    template<class T, class R = T>
+    using t = typename std::enable_if<std::is_enum<T>::value &&
+        enum_traits<T>::allow_bitops, R>::type;
+
+    template<class T>
+    using u = typename std::underlying_type<T>::type;
+};
+
+template<class T>
+constexpr enum_traits<>::t<T> operator~(T a) {
+    return static_cast<T>(~static_cast<enum_traits<>::u<T>>(a));
+}
+template<class T>
+constexpr enum_traits<>::t<T> operator|(T a, T b) {
+    return static_cast<T>(
+        static_cast<enum_traits<>::u<T>>(a) |
+        static_cast<enum_traits<>::u<T>>(b));
+}
+template<class T>
+constexpr enum_traits<>::t<T> operator&(T a, T b) {
+    return static_cast<T>(
+        static_cast<enum_traits<>::u<T>>(a) &
+        static_cast<enum_traits<>::u<T>>(b));
+}
+template<class T>
+constexpr enum_traits<>::t<T> operator^(T a, T b) {
+    return static_cast<T>(
+        static_cast<enum_traits<>::u<T>>(a) ^
+        static_cast<enum_traits<>::u<T>>(b));
+}
+template<class T>
+constexpr enum_traits<>::t<T, T&> operator|=(T& a, T b) {
+    a = a | b;
+    return a;
+}
+template<class T>
+constexpr enum_traits<>::t<T, T&> operator&=(T& a, T b) {
+    a = a & b;
+    return a;
+}
+template<class T>
+constexpr enum_traits<>::t<T, T&> operator^=(T& a, T b) {
+    a = a ^ b;
+    return a;
+}
+
+#define ENABLE_BITMASK_OPERATORS(x)  \
+template<>                           \
+struct enum_traits<x> :              \
+       enum_traits<>::allow_bitops {};
diff --git a/src/Base/CMakeLists.txt b/src/Base/CMakeLists.txt
index e3933d0541..c954558fcd 100644
--- a/src/Base/CMakeLists.txt
+++ b/src/Base/CMakeLists.txt
@@ -280,6 +280,7 @@ SET(FreeCADBase_HPP_SRCS
     Base64.h
     BaseClass.h
     BindingManager.h
+    Bitmask.h
     BoundBox.h
     Builder3D.h
     Console.h