Add std::experimental::optional as Utils::optional

Uses the reference implementation of the proposal, which later
can be replaced by the std lib implementation depending on compiler
and used C++ version.

Change-Id: I23f2f8077f4cb26c3d9a403b1ce438b6cdb163f2
Reviewed-by: Tobias Hunger <tobias.hunger@qt.io>

3 files changed, 63 insertions, 1 deletions

diff --git a/src/libs/utils/optional.h b/src/libs/utils/optional.h
new file mode 100644
index 0000000000..1960297de4
--- /dev/null
+++ b/src/libs/utils/optional.h
@@ -0,0 +1,58 @@
+/****************************************************************************
+**
+** Copyright (C) 2017 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of Qt Creator.
+**
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 3 as published by the Free Software
+** Foundation with exceptions as appearing in the file LICENSE.GPL3-EXCEPT
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-3.0.html.
+**
+****************************************************************************/
+
+#pragma once
+
+/*
+    optional<T>
+    make_optional(t)
+
+    See std(::experimental)::optional.
+*/
+
+// TODO: replace by #include <(experimental/)optional> depending on compiler and C++ version
+#include <3rdparty/optional/optional.hpp>
+
+namespace Utils {
+
+// --> Utils::optional
+using std::experimental::optional;
+// --> Utils::nullopt
+using std::experimental::nullopt;
+
+// TODO: make_optional is a copy, since there is no sensible way to import functions in C++
+template <class T>
+constexpr optional<typename std::decay<T>::type> make_optional(T&& v)
+{
+  return optional<typename std::decay<T>::type>(std::experimental::constexpr_forward<T>(v));
+}
+
+template <class X>
+constexpr optional<X&> make_optional(std::reference_wrapper<X> v)
+{
+  return optional<X&>(v.get());
+}
+
+} // Utils
diff --git a/src/libs/utils/utils-lib.pri b/src/libs/utils/utils-lib.pri
index ef988e76e0..a20a41d159 100644
--- a/src/libs/utils/utils-lib.pri
+++ b/src/libs/utils/utils-lib.pri
@@ -237,7 +237,9 @@ HEADERS += \
     $$PWD/smallstringio.h \
     $$PWD/guard.h \
     $$PWD/asconst.h \
-    $$PWD/smallstringfwd.h
+    $$PWD/smallstringfwd.h \
+    $$PWD/optional.h \
+    $$PWD/../3rdparty/optional/optional.hpp
 
 FORMS += $$PWD/filewizardpage.ui \
     $$PWD/projectintropage.ui \
diff --git a/src/libs/utils/utils.qbs b/src/libs/utils/utils.qbs
index 651135d7fa..03a47ae060 100644
--- a/src/libs/utils/utils.qbs
+++ b/src/libs/utils/utils.qbs
@@ -142,6 +142,8 @@ Project {
             "newclasswidget.cpp",
             "newclasswidget.h",
             "newclasswidget.ui",
+            "optional.h",
+            "../3rdparty/optional/optional.hpp",
             "osspecificaspects.h",
             "outputformat.h",
             "outputformatter.cpp",