From 2c9529e158fc589c48e6b1fb61dca2133e33ac4d Mon Sep 17 00:00:00 2001 From: Marc Mutz Date: Wed, 20 May 2020 15:20:07 +0200 Subject: Long live Q{Any,Utf8}StringView! We need to add these two classes at the same time, because QAnyStringView makes all QUtf8StringView relational operators moot. We might want to add some later, esp. for UTF-8/UTf-8 comparisons, to avoid the pessimization that we can't early-out on size() mismatch in QAnyStringView equality operators, but that's an optimization, not a correctness issue, and can be fixed in a source-compatible way even after Qt 6 is released. To deal with the char8_t problem in C++20, make QUtf8StringView a class template out of which two UTF-8 views can be instantiated: the Qt 7 version, which depends on C++20 char8_t as value_type, and the Qt 6 version where value_type is a char. Use inline namespaces to map the QUtf8StringView identifier to one or the other, depending on the C++ version used to compile the user code. The inline namespace names must needs be a bit ugly, as their inline'ness depends on __cpp_char8_t. If we simply used q_v1/q_v2 we'd be blocking these names for Qt inline namespaces forever, because it's likely that inline'ness of other users of inline namespaces in Qt depends on things other than __cpp_char8_t. While inline'ness of namespaces is, theoretically speaking, a compile-time-only property, at least Clang warns about mixed use of inline on a given namespace, so we need to bite the bullet here. This is also the reason for the QT_BEGIN_..._NAMESPACE macros: GCC is ok with the first declaration making a namespace inline, while Clang warns upon re-opening an inline namespace as a non-inline one. [ChangeLog][QtCore][QUtf8StringView] New class. [ChangeLog][QtCore][QAnyStringView] New class. Change-Id: Ia7179760fca0e0b67d52f5accb0a62e389b17913 Reviewed-by: Lars Knoll --- .../code/src_corelib_text_qutf8stringview.cpp | 59 ++++++++++++++++++++++ 1 file changed, 59 insertions(+) create mode 100644 src/corelib/doc/snippets/code/src_corelib_text_qutf8stringview.cpp (limited to 'src/corelib/doc/snippets/code/src_corelib_text_qutf8stringview.cpp') diff --git a/src/corelib/doc/snippets/code/src_corelib_text_qutf8stringview.cpp b/src/corelib/doc/snippets/code/src_corelib_text_qutf8stringview.cpp new file mode 100644 index 0000000000..b1033371b1 --- /dev/null +++ b/src/corelib/doc/snippets/code/src_corelib_text_qutf8stringview.cpp @@ -0,0 +1,59 @@ +/**************************************************************************** +** +** Copyright (C) 2020 Klarälvdalens Datakonsult AB, a KDAB Group company, info@kdab.com, author Marc Mutz +** Contact: https://www.qt.io/licensing/ +** +** This file is part of the documentation of the Qt Toolkit. +** +** $QT_BEGIN_LICENSE:BSD$ +** 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. +** +** BSD License Usage +** Alternatively, you may use this file under the terms of the BSD license +** as follows: +** +** "Redistribution and use in source and binary forms, with or without +** modification, are permitted provided that the following conditions are +** met: +** * Redistributions of source code must retain the above copyright +** notice, this list of conditions and the following disclaimer. +** * Redistributions in binary form must reproduce the above copyright +** notice, this list of conditions and the following disclaimer in +** the documentation and/or other materials provided with the +** distribution. +** * Neither the name of The Qt Company Ltd nor the names of its +** contributors may be used to endorse or promote products derived +** from this software without specific prior written permission. +** +** +** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS +** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT +** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR +** A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT +** OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, +** SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT +** LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, +** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY +** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT +** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE +** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE." +** +** $QT_END_LICENSE$ +** +****************************************************************************/ + +//! [0] + void myfun1(QUtf8StringView sv); // preferred + void myfun2(const QUtf8StringView &sv); // compiles and works, but slower +//! [0] + +//! [2] + auto sv1 = QUtf8StringView{std::begin(array), std::end(array)}; // using C++11 std::begin()/std::end() + auto sv2 = QUtf8StringView(array, std::size(array)); // using C++17 std::size() +//! 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