corelib/tools: add qMakeArray() API

This function can be used to create std::array without the need
to explicitly provide the size of array. It also has a specialization
that allow to generate sorted array at compile time. Sorted array can
be beneficial for example in binary search.

Change-Id: Ifc7e06e451812fce2ab94293959db5e9cc038793
Reviewed-by: Gatis Paeglis <gatis.paeglis@qt.io>

5 files changed, 288 insertions, 0 deletions

diff --git a/src/corelib/tools/qmakearray_p.h b/src/corelib/tools/qmakearray_p.h
new file mode 100644
index 0000000000..ae4d7f07c6
--- /dev/null
+++ b/src/corelib/tools/qmakearray_p.h
@@ -0,0 +1,179 @@
+/****************************************************************************
+**
+** Copyright (C) 2018 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the QtCore module of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** 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 Lesser General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU Lesser
+** General Public License version 3 as published by the Free Software
+** Foundation and appearing in the file LICENSE.LGPL3 included in the
+** packaging of this file. Please review the following information to
+** ensure the GNU Lesser General Public License version 3 requirements
+** will be met: https://www.gnu.org/licenses/lgpl-3.0.html.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 2.0 or (at your option) the GNU General
+** Public license version 3 or any later version approved by the KDE Free
+** Qt Foundation. The licenses are as published by the Free Software
+** Foundation and appearing in the file LICENSE.GPL2 and LICENSE.GPL3
+** 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-2.0.html and
+** https://www.gnu.org/licenses/gpl-3.0.html.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#ifndef QMAKEARRAY_P_H
+#define QMAKEARRAY_P_H
+
+//
+//  W A R N I N G
+//  -------------
+//
+// This file is not part of the Qt API.  It exists purely as an
+// implementation detail.  This header file may change from version to
+// version without notice, or even be removed.
+//
+// We mean it.
+//
+
+#include "QtCore/qglobal.h"
+
+#include <array>
+#include <type_traits>
+#include <utility>
+
+QT_BEGIN_NAMESPACE
+
+namespace QtPrivate {
+template<typename T>
+constexpr T&& Forward(typename std::remove_reference<T>::type& t) noexcept
+{
+    return static_cast<T&&>(t);
+}
+
+template<typename T>
+constexpr T&& Forward(typename std::remove_reference<T>::type&& t) noexcept
+{
+    static_assert(!std::is_lvalue_reference<T>::value,
+                  "template argument substituting T is an lvalue reference type");
+    return static_cast<T&&>(t);
+}
+
+template <typename ManualType, typename ...>
+struct ArrayTypeHelper
+{
+    using type = ManualType;
+};
+
+template <typename ... Types>
+struct ArrayTypeHelper<void, Types...> : std::common_type<Types...> { };
+
+template <typename ManualType, typename... Types>
+using ArrayType = std::array<typename ArrayTypeHelper<ManualType, Types...>::type,
+                             sizeof...(Types)>;
+
+template<typename ... Values>
+struct QuickSortData { };
+
+template <template <typename> class Predicate,
+          typename ... Values>
+struct QuickSortFilter;
+
+template <typename ... Right, typename ... Left>
+constexpr QuickSortData<Right..., Left...> quickSortConcat(
+    QuickSortData<Right...>, QuickSortData<Left...>) noexcept;
+
+template<typename ... Right, typename Middle, typename ... Left>
+constexpr QuickSortData<Right..., Middle, Left...> quickSortConcat(
+    QuickSortData<Right...>,
+    QuickSortData<Middle>,
+    QuickSortData<Left...>) noexcept;
+
+template <template <typename> class Predicate,
+          typename Head, typename ... Tail>
+struct QuickSortFilter<Predicate, QuickSortData<Head, Tail...>>
+{
+    using TailFilteredData = typename QuickSortFilter<
+        Predicate, QuickSortData<Tail...>>::Type;
+
+    using Type = typename QConditional<
+        Predicate<Head>::value,
+        decltype(quickSortConcat(QuickSortData<Head> {}, TailFilteredData{})),
+        TailFilteredData>::Type;
+};
+
+template <template <typename> class Predicate>
+struct QuickSortFilter<Predicate, QuickSortData<>>
+{
+    using Type = QuickSortData<>;
+};
+
+template <typename ... Values>
+struct QuickSort;
+
+template <typename Pivot, typename ... Values>
+struct QuickSort<QuickSortData<Pivot, Values...>>
+{
+    template <typename Left>
+    struct LessThan {
+        static constexpr const bool value = Left::data() <= Pivot::data();
+    };
+
+    template <typename Left>
+    struct MoreThan {
+        static constexpr const bool value = !(Left::data() <= Pivot::data());
+    };
+
+    using LeftSide = typename QuickSortFilter<LessThan, QuickSortData<Values...>>::Type;
+    using RightSide = typename QuickSortFilter<MoreThan, QuickSortData<Values...>>::Type;
+
+    using LeftQS = typename QuickSort<LeftSide>::Type;
+    using RightQS = typename QuickSort<RightSide>::Type;
+
+    using Type = decltype(quickSortConcat(LeftQS{}, QuickSortData<Pivot> {}, RightQS{}));
+
+};
+
+template <>
+struct QuickSort<QuickSortData<>>
+{
+    using Type = QuickSortData<>;
+};
+} // namespace QtPrivate
+
+template <typename ManualType = void, typename ... Types>
+constexpr QtPrivate::ArrayType<ManualType, Types...> qMakeArray(Types && ... t) noexcept
+{
+    return {{QtPrivate::Forward<typename QtPrivate::ArrayType<ManualType, Types...>::value_type>(t)...}};
+}
+
+template<typename ... Values>
+struct QSortedData {
+    using Data = typename QtPrivate::QuickSort<typename QtPrivate::QuickSortData<Values...>>::Type;
+};
+
+template<typename ... Values>
+constexpr auto qMakeArray(QtPrivate::QuickSortData<Values...>) noexcept -> decltype(qMakeArray(Values::data()...))
+{
+    return qMakeArray(Values::data() ...);
+}
+
+
+QT_END_NAMESPACE
+
+#endif // QMAKEARRAY_P_H
diff --git a/src/corelib/tools/tools.pri b/src/corelib/tools/tools.pri
index 4f2d3dd4a3..7a74dfda3e 100644
--- a/src/corelib/tools/tools.pri
+++ b/src/corelib/tools/tools.pri
@@ -34,6 +34,7 @@ HEADERS +=  \
         tools/qlocale_p.h \
         tools/qlocale_tools_p.h \
         tools/qlocale_data_p.h \
+        tools/qmakearray_p.h \
         tools/qmap.h \
         tools/qmargins.h \
         tools/qmessageauthenticationcode.h \
diff --git a/tests/auto/corelib/tools/qmakearray/qmakearray.pro b/tests/auto/corelib/tools/qmakearray/qmakearray.pro
new file mode 100644
index 0000000000..abb3d9fdbc
--- /dev/null
+++ b/tests/auto/corelib/tools/qmakearray/qmakearray.pro
@@ -0,0 +1,4 @@
+CONFIG += testcase
+TARGET = tst_qmakearray
+QT = core testlib core-private
+SOURCES = $$PWD/tst_qmakearray.cpp
diff --git a/tests/auto/corelib/tools/qmakearray/tst_qmakearray.cpp b/tests/auto/corelib/tools/qmakearray/tst_qmakearray.cpp
new file mode 100644
index 0000000000..e0d3f52719
--- /dev/null
+++ b/tests/auto/corelib/tools/qmakearray/tst_qmakearray.cpp
@@ -0,0 +1,103 @@
+/****************************************************************************
+**
+** Copyright (C) 2018 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the test suite of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:GPL-EXCEPT$
+** 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.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#include <QtTest/QtTest>
+
+#include <private/qmakearray_p.h>
+
+
+class tst_QMakeArray : public QObject
+{
+    Q_OBJECT
+
+private slots:
+    void quicksort();
+};
+
+struct Pair {
+    unsigned int key;
+    unsigned int val;
+
+    constexpr bool operator <=(const Pair &that) const noexcept
+    {
+        return key <= that.key;
+    }
+
+    constexpr bool operator<(const Pair &that) const noexcept
+    {
+        return key < that.key;
+    }
+
+    constexpr bool operator==(const Pair &that) const noexcept
+    {
+        return key == that.key;
+    }
+};
+
+template<std::size_t Key, std::size_t Val>
+struct PairQuickSortElem
+{
+    using Type = Pair;
+    static constexpr Type data() noexcept { return Type{Key, Val}; }
+};
+
+void tst_QMakeArray::quicksort()
+{
+    constexpr const auto sorted_array = qMakeArray(
+        QSortedData<
+            PairQuickSortElem<10, 0>,
+            PairQuickSortElem<5, 0>,
+            PairQuickSortElem<7, 0>,
+            PairQuickSortElem<1, 0>,
+            PairQuickSortElem<8, 0>,
+            PairQuickSortElem<6, 0>,
+            PairQuickSortElem<4, 0>,
+            PairQuickSortElem<3, 0>,
+            PairQuickSortElem<1, 0>,
+            PairQuickSortElem<2, 0>,
+            PairQuickSortElem<10, 0>,
+            PairQuickSortElem<5, 0>
+        >::Data{});
+    static_assert(sorted_array.size() == 12, "sorted_array.size() != 12");
+    QCOMPARE(sorted_array[0].key, 1u);
+    QCOMPARE(sorted_array[1].key, 1u);
+    QCOMPARE(sorted_array[2].key, 2u);
+    QCOMPARE(sorted_array[3].key, 3u);
+    QCOMPARE(sorted_array[4].key, 4u);
+    QCOMPARE(sorted_array[5].key, 5u);
+    QCOMPARE(sorted_array[6].key, 5u);
+    QCOMPARE(sorted_array[7].key, 6u);
+    QCOMPARE(sorted_array[8].key, 7u);
+    QCOMPARE(sorted_array[9].key, 8u);
+    QCOMPARE(sorted_array[10].key, 10u);
+    QCOMPARE(sorted_array[11].key, 10u);
+}
+
+
+QTEST_APPLESS_MAIN(tst_QMakeArray)
+#include "tst_qmakearray.moc"
diff --git a/tests/auto/corelib/tools/tools.pro b/tests/auto/corelib/tools/tools.pro
index f35ed026ac..f28cf21b8b 100644
--- a/tests/auto/corelib/tools/tools.pro
+++ b/tests/auto/corelib/tools/tools.pro
@@ -30,6 +30,7 @@ SUBDIRS=\
     qlist \
     qlist_strictiterators \
     qlocale \
+    qmakearray \
     qmap \
     qmap_strictiterators \
     qmargins \