Short live q20::ssize()!

Extract the definition of q20::ssize() from tst_qanystringview.cpp,
where it had to be placed for its backport to 6.2.

Change-Id: I3f758c98a4b1efd453f4fc044b8d3f1a89de62d1
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>
Reviewed-by: Andrei Golubev <andrei.golubev@qt.io>

2 files changed, 81 insertions, 0 deletions

diff --git a/src/corelib/CMakeLists.txt b/src/corelib/CMakeLists.txt
index 7b4a16e5ce..ecadec689b 100644
--- a/src/corelib/CMakeLists.txt
+++ b/src/corelib/CMakeLists.txt
@@ -63,6 +63,7 @@ qt_internal_add_module(Core
         global/qvolatile_p.h
         global/q20algorithm.h
         global/q20functional.h
+        global/q20iterator.h
         io/qabstractfileengine.cpp io/qabstractfileengine_p.h
         io/qbuffer.cpp io/qbuffer.h
         io/qdataurl.cpp io/qdataurl_p.h
diff --git a/src/corelib/global/q20iterator.h b/src/corelib/global/q20iterator.h
new file mode 100644
index 0000000000..7c65aeb856
--- /dev/null
+++ b/src/corelib/global/q20iterator.h
@@ -0,0 +1,80 @@
+/****************************************************************************
+**
+** Copyright (C) 2021 The Qt Company Ltd.
+** Contact: http://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 Q20ITERATOR_H
+#define Q20ITERATOR_H
+
+#include <QtCore/qglobal.h>
+
+#include <iterator>
+
+//
+//  W A R N I N G
+//  -------------
+//
+// This file is not part of the Qt API. Types and functions defined
+// in this file will behave exactly as their std counterparts. You
+// may use these definitions in your own code, but be aware that we
+// will remove them once Qt depends on the C++ version that supports
+// them in namespace std. There will be NO deprecation warning, the
+// definitions will JUST go away.
+//
+// If you can't agree to these terms, don't use these definitions!
+//
+// We mean it.
+//
+
+QT_BEGIN_NAMESPACE
+
+// like std::ssize
+namespace q20 {
+#ifdef __cpp_lib_ssize
+    using std::ssize;
+#else
+    template<class C> constexpr auto ssize(const C &c)
+      -> std::common_type_t<std::ptrdiff_t, std::make_signed_t<decltype(c.size())>>
+    { return static_cast<std::common_type_t<std::ptrdiff_t, std::make_signed_t<decltype(c.size())>>>(c.size()); }
+
+    template<class T, std::ptrdiff_t N> constexpr std::ptrdiff_t ssize(const T (&)[N]) noexcept
+    { return N; }
+#endif
+} // namespace q20
+
+QT_END_NAMESPACE
+
+#endif /* Q20ITERATOR_H */