warning: implicitly-declared ‘constexpr QJsonValueRef::QJsonValueRef(const QJsonValueRef&)’ is deprecated

[Gilbert Lee]

The following code generates the a warning message.

#include <QJsonObject>

QJsonValueRef operator << (QJsonValueRef ref, int) {
	return ref;
}

int main() {
	QJsonObject jo;
	jo["foo"] << 1;
}

warning: implicitly-declared ‘constexpr QJsonValueRef::QJsonValueRef(const QJsonValueRef&)’ is deprecated

$ qmake --version
QMake version 3.1
Using Qt version 5.14.2 in /opt/Qt/5.14.2/gcc_64/lib

Thank you in advance.

[Christian Ehrlicher]

Don't copy the QJsonValue, pass it by reference. Also I don't understand what the operator in your example should do at all.

[Gilbert Lee]

@Christian-Ehrlicher

It's a code which just shows a warning message that copy constructor does not exist in QJsonValueRef class, and QJsonValueRef is a reference class of QJsonValue.

[Gilbert Lee]

FYI,
https://en.cppreference.com/w/cpp/language/rule_of_three