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By moving the base fields to a QObjectBase_, QObject can be a type which also has a 'base' field. This allows writing a generic QOBJECT() macro that will work with any QObject type, including QObject itself. The container_of() macro ensures that the object to cast has a QObjectBase_ base field, giving some type safety guarantees. QObject must have no members but QObjectBase_ base, or else QOBJECT() breaks. QObjectBase_ is not a typedef and uses a trailing underscore to make it obvious it is not for normal use and to avoid potential abuse. Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com> Reviewed-by: Eric Blake <eblake@redhat.com> Message-Id: <20180419150145.24795-3-marcandre.lureau@redhat.com> Reviewed-by: Markus Armbruster <armbru@redhat.com> Signed-off-by: Markus Armbruster <armbru@redhat.com>
33 lines
547 B
C
33 lines
547 B
C
/*
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* QNull
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*
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* Copyright (C) 2015 Red Hat, Inc.
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*
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* Authors:
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* Markus Armbruster <armbru@redhat.com>
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*
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* This work is licensed under the terms of the GNU LGPL, version 2.1
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* or later. See the COPYING.LIB file in the top-level directory.
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*/
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#ifndef QNULL_H
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#define QNULL_H
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#include "qapi/qmp/qobject.h"
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struct QNull {
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struct QObjectBase_ base;
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};
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extern QNull qnull_;
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static inline QNull *qnull(void)
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{
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QINCREF(&qnull_);
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return &qnull_;
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}
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bool qnull_is_equal(const QObject *x, const QObject *y);
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#endif /* QNULL_H */
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