Qt implicitly shared class demo 隐式共享

Employee.cpp

#include "Employee.h"
#include <QString>

class EmployeeData : public QSharedData
{
public:
	EmployeeData()
	    : id(-1)
	{}

	// 要在这个构造函数中赋值
	EmployeeData(const EmployeeData& other)
	    : QSharedData(other)
	    , id(other.id)
	    , name(other.name)
	{}

	~EmployeeData() { qDebug("~EmployeeData %d", id); }

	int     id;
	QString name;
};

Employee::Employee()
    : d(new EmployeeData)
{
}

Employee::Employee(int id, const QString& name)
    : d(new EmployeeData)
{
	setId(id);
	setName(name);
}

Employee::~Employee()
{
	qDebug("~Employee()");
}

Employee::Employee(const Employee& other)
    : d(other.d)
{}

Employee& Employee::operator=(const Employee& other)
{
	d = other.d;
	return *this;
}

void Employee::setId(int id)
{
	d->id = id;
}

void Employee::setName(const QString &name)
{
    d->name = name;
}

int Employee::id() const
{
    return d->id;
}

QString Employee::name() const
{
    return d->name;
}

Employee.h

#ifndef EMPLOYEE_H
#define EMPLOYEE_H

#include <QSharedDataPointer>

class QString;

// Demo from https://doc.qt.io/qt-6/qshareddatapointer.html
class EmployeeData;
class Employee
{
public:
	Employee();
	Employee(int id, const QString& name);
	virtual ~Employee();

	// Qt文档：若EmployeeData所有成员已经在本头文件中声明，
	// 则无需实现拷贝构造函数和赋值构造函数
	// 本例子由于隐藏了EmployeeData的实现，故要手动实现
	Employee(const Employee& other);
	Employee& operator=(const Employee&);

	void setId(int id);
	void setName(const QString& name);

	int     id() const;
	QString name() const;

private:
	QSharedDataPointer<EmployeeData> d;
};

#endif // EMPLOYEE_H

main.cpp

#include <QCoreApplication>
#include "Employee.h"

int main(int argc, char *argv[])
{
	QCoreApplication app(argc, argv);
	Q_UNUSED(app)

	{
		qDebug("\ntest operator=()");
		Employee e1(100, "AAAA");
		Employee e2(200, "BBBB");
		e1 = e2;
	}

	{
		qDebug("\ntest copy constructor()");
		Employee e1(100, "AAAA");
		Employee e2(e1);
		Q_UNUSED(e2)
	}

	{
		qDebug("\ntest e2.setId()");
		Employee e1(100, "AAAA");
		Employee e2(e1);
		e2.setId(99999);
	}

	return 0;
}