Add a QMetaSequence interface

This is in line with QMetaType and will be used to implement a mutable
QSequentialIterable. Later on, a QMetaAssociation will be added as
well, to implement a mutable QAssociativeIterable.

The code here represents the minimal set of functionality needed to have
a practical sequential container. The functionality is not completely
orthogonal. In particular, the index based operations could be
implemented in terms of iterator-based operations.

Task-number: QTBUG-81716
Change-Id: Ibd41eb7db248a774673c701549d9a03cbf2e48b6
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>

2 files changed, 151 insertions, 0 deletions

diff --git a/src/corelib/global/global.pri b/src/corelib/global/global.pri
index 6ba39d41bd..e799e13e4c 100644
--- a/src/corelib/global/global.pri
+++ b/src/corelib/global/global.pri
@@ -6,6 +6,7 @@ HEADERS +=  \
         global/qoperatingsystemversion_p.h \
         global/qsystemdetection.h \
         global/qcompilerdetection.h \
+        global/qcontainerinfo.h \
         global/qprocessordetection.h \
         global/qmemory_p.h \
 	global/qnamespace.h \
diff --git a/src/corelib/global/qcontainerinfo.h b/src/corelib/global/qcontainerinfo.h
new file mode 100644
index 0000000000..ad3ef301e4
--- /dev/null
+++ b/src/corelib/global/qcontainerinfo.h
@@ -0,0 +1,150 @@
+/****************************************************************************
+**
+** Copyright (C) 2020 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 QCONTAINERINFO_H
+#define QCONTAINERINFO_H
+
+#include <QtCore/qglobal.h>
+#include <type_traits>
+
+QT_BEGIN_NAMESPACE
+
+namespace QContainerTraits
+{
+
+template<typename C>
+using value_type = typename C::value_type;
+
+template<typename C>
+using iterator = typename C::iterator;
+
+template<typename C>
+using const_iterator = typename C::const_iterator;
+
+// Some versions of Apple clang warn about the constexpr variables below being unused.
+QT_WARNING_PUSH
+QT_WARNING_DISABLE_CLANG("-Wunused-const-variable")
+
+template<typename C, typename = void>
+constexpr bool has_size_v = false;
+template<typename C>
+constexpr bool has_size_v<C, std::void_t<decltype(C().size())>> = true;
+
+template<typename C, typename = void>
+constexpr bool has_clear_v = false;
+template<typename C>
+constexpr bool has_clear_v<C, std::void_t<decltype(C().clear())>> = true;
+
+template<typename, typename = void>
+constexpr bool has_at_v = false;
+template<typename C>
+constexpr bool has_at_v<C, std::void_t<decltype(C().at(0))>> = true;
+
+template<typename, typename = void>
+constexpr bool can_get_at_index_v = false;
+template<typename C>
+constexpr bool can_get_at_index_v<C, std::void_t<value_type<C>(decltype(C()[0]))>> = true;
+
+template<typename, typename = void>
+constexpr bool can_set_at_index_v = false;
+template<typename C>
+constexpr bool can_set_at_index_v<C, std::void_t<decltype(C()[0] = value_type<C>())>> = true;
+
+template<typename, typename = void>
+constexpr bool has_push_front_v = false;
+template<typename C>
+constexpr bool has_push_front_v<C, std::void_t<decltype(C().push_front(value_type<C>()))>> = true;
+
+template<typename, typename = void>
+constexpr bool has_push_back_v = false;
+template<typename C>
+constexpr bool has_push_back_v<C, std::void_t<decltype(C().push_back(value_type<C>()))>> = true;
+
+template<typename, typename = void>
+constexpr bool has_insert_v = false;
+template<typename C>
+constexpr bool has_insert_v<C, std::void_t<decltype(C().insert(value_type<C>()))>> = true;
+
+template<typename, typename = void>
+constexpr bool has_pop_front_v = false;
+template<typename C>
+constexpr bool has_pop_front_v<C, std::void_t<decltype(C().pop_front())>> = true;
+
+template<typename, typename = void>
+constexpr bool has_pop_back_v = false;
+template<typename C>
+constexpr bool has_pop_back_v<C, std::void_t<decltype(C().pop_back())>> = true;
+
+template<typename, typename = void>
+constexpr bool has_iterator_v = false;
+template<typename C>
+constexpr bool has_iterator_v<C, std::void_t<iterator<C>>> = true;
+
+template<typename, typename = void>
+constexpr bool has_const_iterator_v = false;
+template<typename C>
+constexpr bool has_const_iterator_v<C, std::void_t<const_iterator<C>>> = true;
+
+template<typename, typename = void>
+constexpr bool can_get_at_iterator_v = false;
+template<typename C>
+constexpr bool can_get_at_iterator_v<C, std::void_t<value_type<C>(decltype(*C().begin()))>> = true;
+
+template<typename, typename = void>
+constexpr bool can_set_at_iterator_v = false;
+template<typename C>
+constexpr bool can_set_at_iterator_v<C, std::void_t<decltype(*C().begin() = value_type<C>())>> = true;
+
+template<typename, typename = void>
+constexpr bool can_insert_at_iterator_v = false;
+template<typename C>
+constexpr bool can_insert_at_iterator_v<C, std::void_t<decltype(C().insert(C().begin(), value_type<C>()))>> = true;
+
+template<typename, typename = void>
+constexpr bool can_erase_at_iterator_v = false;
+template<typename C>
+constexpr bool can_erase_at_iterator_v<C, std::void_t<decltype(C().erase(C().begin()))>> = true;
+
+QT_WARNING_POP
+
+}
+
+QT_END_NAMESPACE
+
+#endif // QCONTAINERINFO_H