1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
|
/****************************************************************************
**
** Copyright (C) 2020 The Qt Company Ltd.
** Contact: https://www.qt.io/licensing/
**
** This file is part of the documentation of the Qt Toolkit.
**
** $QT_BEGIN_LICENSE:FDL$
** 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 Free Documentation License Usage
** Alternatively, this file may be used under the terms of the GNU Free
** Documentation License version 1.3 as published by the Free Software
** Foundation and appearing in the file included in the packaging of
** this file. Please review the following information to ensure
** the GNU Free Documentation License version 1.3 requirements
** will be met: https://www.gnu.org/licenses/fdl-1.3.html.
** $QT_END_LICENSE$
**
****************************************************************************/
/*!
\page qtcore-changes-qt6.html
\title Porting to Qt 6 - Qt Core
\ingroup porting-guides-5-to-6
\brief Migrate Qt Core to Qt 6.
Qt 6 is a result of the conscious effort to make the framework more
efficient and easy to use.
We try to maintain binary and source compatibility for all the public
APIs in each release. But some changes were inevitable in an effort to
make Qt a better framework.
In this topic we summarize those changes in Qt Core, and provide guidance
to handle them.
\section1 Container Classes
\section2 QHash, QMultiHash, QSet
\section3 qHash() Signature
For custom types, QHash and QMultiHash rely on you providing
a \l{The qHash() hashing function} {custom qHash() function}
in the same namespace. In Qt 4 and Qt 5, the return
value and optional second argument of a \c qHash function
was of type \c uint. In Qt 6, it is \c size_t.
That is, you need to change
\code
uint qHash(MyType x, uint seed);
\endcode
to
\code
size_t qHash(MyType x, size_t seed);
\endcode
This allows QHash, QMultiHash and QSet to hold more than 2^32 items on
64 bit platforms.
\section3 Stability of References
The implementation of QHash and QMultiHash in Qt 6 got changed from
a node based approach to a two stage lookup table. This design allows
to keep the memory overhead of a hash instance very small, while
at the same time giving good performance.
One behavioral change to note is that the new QHash implementation
will not provide stable references to elements in the hash when the
table needs to grow, or when entries are removed. Applications that
rely on such stability might now run into undefined behavior.
\section3 Removal of QHash::insertMulti
In Qt 5, QHash could be used to create multi-valued hashes by using
QHash::insertMulti, and QMultiHash was deriving vom QHash.
In Qt 6, both types and use cases are distinct, and QHash::insertMulti
got removed.
*/
|
