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// Copyright (C) 2025 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
// Qt-Security score:significant reason:default
#ifndef QTCLASSHELPER_P_H
#define QTCLASSHELPER_P_H
#include <QtCore/private/qglobal_p.h>
//
// W A R N I N G
// -------------
//
// This file is not part of the Qt API. It exists purely as an
// implementation detail. This header file may change from version to
// version without notice, or even be removed.
//
// We mean it.
//
#include <type_traits>
#include <utility>
QT_BEGIN_NAMESPACE
/*
Helper for setters overloaded on lvalue/rvalue. If the setter is doing a
lot of work around the actual assignment, a common pattern is to create a
private helper method
void doSetFoo(const Foo &lvalue, Foo *rvalue);
and implement the two setters inline by calling that function:
void setFoo(const Foo &f) { doSetFoo(f, nullptr); }
void setFoo(Foo &&f) { doSetFoo(f, &f); }
Then, in doSetFoo(), when assigning the argument to the member, use this
function:
q_choose_assign(m_foo, lvalue, rvalue);
or, when appending to a container,
q_choose_append(m_container, lvalue, rvalue);
For all other purposes, you can use
q_choose_copy_move(lvalue, rvalue);
though note that this always produces an rvalue (the copy, if any, is done
inside the function).
The functions mandate (in the C++ sense) that all arguments are the same
type, so they deduce each argument separately and then static_assert that
they're the same. If we need std::exchange()-like mixed types later, it's
easy to relax. For now, avoid being overly general.
*/
template <typename U, typename V>
U q_choose_copy_move(const U &lvalue, V *rvalue)
{
static_assert(std::is_same_v<U, V>, "all arguments must be of the same type");
if (rvalue)
return std::move(*rvalue);
else
return lvalue;
}
template <typename T, typename U, typename V>
decltype(auto) q_choose_assign(T &var, const U &lvalue, V *rvalue)
{
static_assert(std::is_same_v<T, U>, "all arguments must be of the same type");
static_assert(std::is_same_v<U, V>, "all arguments must be of the same type");
if (rvalue)
return var = std::move(*rvalue);
else
return var = lvalue;
}
template <typename Container, typename U, typename V>
decltype(auto) q_choose_append(Container &c, const U &lvalue, V *rvalue)
{
static_assert(std::is_same_v<typename Container::value_type, U>, "arguments must match container");
static_assert(std::is_same_v<U, V>, "all arguments must be of the same type");
if (rvalue)
c.push_back(std::move(*rvalue));
else
c.push_back(lvalue);
return c.back();
}
QT_END_NAMESPACE
#endif // QTCLASSHELPER_P_H