kgameproperty.h

/*
    This file is part of the KDE games library
    SPDX-FileCopyrightText: 2001 Andreas Beckermann <[email protected]>
    SPDX-FileCopyrightText: 2001 Martin Heni <kde at heni-online.de>
 
    SPDX-License-Identifier: LGPL-2.0-only
*/
 
#ifndef __KGAMEPROPERTY_H_
#define __KGAMEPROPERTY_H_
 
// own
#include "libkdegamesprivate_export.h"
// Qt
#include <QDataStream>
#include <QDebug>
#include <QIODevice>
// Std
#include <typeinfo>
 
class KGame;
class KPlayer;
class KGamePropertyHandler;
using namespace std;
 
/**
 * \class KGamePropertyBase kgameproperty.h <KGame/KGameProperty>
 *
 * @short Base class of KGameProperty
 *
 * The KGamePropertyBase class is the base class of KGameProperty. See
 * KGameProperty for further information.
 *
 * @author Andreas Beckermann <[email protected]>
 **/
class KDEGAMESPRIVATE_EXPORT KGamePropertyBase
{
public:
    enum PropertyDataIds  { // these belong to KPlayer/KGame!
        //KPlayer
        IdGroup=1,
        IdUserId=2,
        IdAsyncInput=3,
        IdTurn=4,
        IdName=5,
 
        //KGame
        IdGameStatus=6,
        IdMaxPlayer=7,
        IdMinPlayer=8,
 
    // Input Grabbing
    IdGrabInput=16,
    IdReleaseInput=17,
 
        IdCommand, // Reserved for internal use
        IdUser=256,
 
        IdAutomatic=0x7000  // Id's from here on are automatically given (16bit)
    };
 
    /**
     * Commands for advanced properties (qint8)
     **/
    enum PropertyCommandIds
    {
        // General
        CmdLock=1,
 
        // Array
        CmdAt=51,
        CmdResize=52,
        CmdFill=53,
        CmdSort=54,
        // List (could be the same id's actually)
        CmdInsert=61,
        CmdAppend=62,
        CmdRemove=63,
        CmdClear=64
    };
 
    /**
     * The policy of the property. This can be PolicyClean (setValue uses
     * send), PolicyDirty (setValue uses changeValue) or
     * PolicyLocal (setValue uses setLocal).
     *
     * A "clean" policy means that the property is always the same on every
     * client. This is achieved by calling send which actually changes
     * the value only when the message from the MessageServer is received.
     *
     * A "dirty" policy means that as soon as setValue is called the
     * property is changed immediately. And additionally sent over network.
     * This can sometimes lead to bugs as the other clients do not
     * immediately have the same value. For more information see
     * changeValue.
     *
     * PolicyLocal means that a KGameProperty behaves like ever
     * "normal" variable. Whenever setValue is called (e.g. using "=")
     * the value of the property is changes immediately without sending it
     * over network. You might want to use this if you are sure that all
     * clients set the property at the same time.
     **/
    enum PropertyPolicy
    {
        PolicyUndefined = 0,
        PolicyClean = 1,
        PolicyDirty = 2,
        PolicyLocal = 3
    };
 
 
    /**
     * Constructs a KGamePropertyBase object and calls registerData.
     * @param id The id of this property. MUST be UNIQUE! Used to send and
     * receive changes in the property of the player automatically via
     * network.
     * @param owner The owner of the object. Must be a KGamePropertyHandler which manages
     * the changes made to this object, i.e. which will send the new data
     **/
    KGamePropertyBase(int id, KGamePropertyHandler* owner);
 
    KGamePropertyBase(int id, KGame* parent);
    KGamePropertyBase(int id, KPlayer* parent);
 
    /**
     * Creates a KGamePropertyBase object without an owner. Remember to call
     * registerData!
     **/
    KGamePropertyBase();
 
    virtual ~KGamePropertyBase();
 
    /**
     * Changes the consistency policy of a property. The
     * PropertyPolicy is one of PolicyClean (defaulz), PolicyDirty or PolicyLocal.
     *
     * It is up to you to decide how you want to work.
     **/
    void setPolicy(PropertyPolicy p) { mFlags.bits.policy = p; }
 
    /**
     * @return The default policy of the property
     **/
    PropertyPolicy policy() const { return (PropertyPolicy)mFlags.bits.policy; }
 
    /**
     * Sets this property to emit a signal on value changed.
     * As the properties do not inherit QObject for optimization
     * this signal is emitted via the KPlayer or KGame object
     **/
    void setEmittingSignal(bool p)  { mFlags.bits.emitsignal=p; }
 
    /**
     * See also setEmittingSignal
     * @return Whether this property emits a signal on value change
     **/
    bool isEmittingSignal() const { return mFlags.bits.emitsignal; }
 
    /**
     * Sets this property to try to optimize signal and network handling
     * by not sending it out when the property value is not changed.
     **/
    void setOptimized(bool p) { mFlags.bits.optimize = p ; }
 
    /**
     * See also setOptimize
     * @return Whether the property optimizes access (signals,network traffic)
     **/
    bool isOptimized() const { return mFlags.bits.optimize; }
 
    /**
     * @return Whether this property is "dirty". See also setDirty
     **/
    bool isDirty() const { return mFlags.bits.dirty; }
 
    /**
     * A locked property can only be changed by the player who has set the
     * lock. See also setLocked
     * @return Whether this property is currently locked.
     **/
    bool isLocked() const { return mFlags.bits.locked; }
 
    /**
     * A locked property can only be changed by the player who has set the
     * lock.
     *
     * You can only call this if isLocked is false. A message is sent
     * over network so that the property is locked for all players except
     * you.
     *
     * @return returns false if the property can not be locked, i.e. it is already locked
     *
     **/
    bool lock();
 
    /**
     * A locked property can only be changed by the player who has set the
     * lock.
     *
     * You can only call this if isLocked is false. A message is sent
     * over network so that the property is locked for all players except
     * you.
     *
     * @return returns false if the property can not be locked, i.e. it is already locked
     *
     **/
    bool unlock(bool force=false);
 
    /**
     * This will read the value of this property from the stream. You MUST
     * overwrite this method in order to use this class
     * @param s The stream to read from
     **/
    virtual void load(QDataStream& s) = 0;
 
    /**
     * Write the value into a stream. MUST be overwritten
     **/
    virtual void save(QDataStream& s) = 0;
 
    /**
     * send a command to advanced properties like arrays
     * @param stream The stream containing the data of the command
     * @param msgid The ID of the command - see PropertyCommandIds
     * @param isSender whether this client is also the sender of the command
     **/
    virtual void command(QDataStream &stream, int msgid, bool isSender=false);
 
    /**
     * @return The id of this property
     **/
    int id() const { return mId; }
 
    /**
     * @return a type_info of the data this property contains.
     **/
    virtual const type_info* typeinfo() { return &typeid(this); }
 
    /**
     * You have to register a KGamePropertyBase before you can use it.
     *
     * You MUST call this before you can use KGamePropertyBase!
     *
     * @param id the id of this KGamePropertyBase object. The id MUST be
     * unique, i.e. you cannot have two properties with the same id for one
     * player, although (currently) nothing prevents you from doing so. But
     * you will get strange results!
     *
     * @param owner The owner of this data. This will send the data
     * using KPropertyHandler::sendProperty whenever you call send
     *
     * @param p If not 0 you can set the policy of the property here
     *
     * @param name if not 0 you can assign a name to this property
     *
     **/
    int registerData(int id, KGamePropertyHandler* owner,PropertyPolicy p, const QString& name=QString());
 
    /**
     * This is an overloaded member function, provided for convenience.
     * It differs from the above function only in what argument(s) it accepts.
     **/
    int registerData(int id, KGamePropertyHandler* owner, const QString& name=QString());
 
    /**
     * This is an overloaded member function, provided for convenience.
     * It differs from the above function only in what argument(s) it accepts.
     **/
        int registerData(int id, KGame* owner, const QString& name=QString());
 
    /**
     * This is an overloaded member function, provided for convenience.
     * It differs from the above function only in what argument(s) it accepts.
     **/
        int registerData(int id, KPlayer* owner, const QString& name=QString());
 
    /**
     * This is an overloaded member function, provided for convenience.
     * It differs from the above function only in what argument(s) it accepts.
     * In particular you can use this function to create properties which
     * will have an automatic id assigned. The new id is returned.
     **/
        int registerData(KGamePropertyHandler* owner,PropertyPolicy p=PolicyUndefined, const QString& name=QString() );
 
    void unregisterData();
 
 
protected:
    /**
     * A locked property can only be changed by the player who has set the
     * lock.
     *
     * You can only call this if isLocked is false. A message is sent
     * over network so that the property is locked for all players except
     * you.
     * Usually you use lock and unlock to access this property
     *
     **/
    void setLock(bool l);
 
    /**
     * Sets the "dirty" flag of the property. If a property is "dirty" i.e.
     * KGameProperty::setLocal has been called there is no guarantee
     * that all clients share the same value. You have to ensure this
     * yourself e.g. by calling KGameProperty::setLocal on every
     * client. You can also ignore the dirty flag and continue working withe
     * the property depending on your situation.
     **/
    void setDirty(bool d) { mFlags.bits.dirty = d ; }
 
    /**
     * Forward the data to the owner of this property which then sends it
     * over network. save is used to store the data into a stream so
     * you have to make sure that function is working properly if you
     * implement your own property!
     *
     * Note: this sends the <em>current</em> property!
     *
     * Might be obsolete - KGamePropertyArray still uses it. Is this a bug
     * or correct?
     **/
    bool sendProperty();
 
    /**
     * Forward the data to the owner of this property which then sends it
     * over network. save is used to store the data into a stream so
     * you have to make sure that function is working properly if you
     * implement your own property!
     *
     * This function is used by send to send the data over network.
     * This does <em>not</em> send the current value but the explicitly
     * given value.
     *
     * @return TRUE if the message could be sent successfully, otherwise
     * FALSE
     **/
    bool sendProperty(const QByteArray& b);
 
    /**
     * Causes the parent object to emit a signal on value change
     **/
    void emitSignal();
 
protected:
    KGamePropertyHandler* mOwner;
 
    // Having this as a union of the bitfield and the char
    // allows us to stream this quantity easily (if we need to)
    // At the moment it is not yet transmitted
    union Flags {
        char flag;
        struct {
            // unsigned char dosave : 1;   // do save this property
            // unsigned char delaytransmit : 1;   // do not send immediately on
                                             // change but a KPlayer:QTimer
                                             // sends it later on - fast
                                             // changing variables
            unsigned char emitsignal : 1; // KPlayer notifies on variable change (true)
            //unsigned char readonly : 1; // whether the property can be changed (false)
            unsigned char optimize : 1; // whether the property tries to optimize send/emit (false)
            unsigned char dirty: 1; // whether the property dirty (setLocal() was used)
            unsigned char policy : 2; // whether the property is always consistent (see PropertyPolicy)
            unsigned char locked: 1; // whether the property is locked (true)
        } bits;
    } mFlags;
 
private:
    friend class KGamePropertyHandler;
    void init();
 
private:
    int mId;
 
};
 
/**
 * \class KGameProperty kgameproperty.h <KGame/KGameProperty>
 *
 * @short A class for network transparent games
 *
 * Note: The entire API documentation is obsolete!
 *
 * The class KGameProperty can store any form of data and will transmit it via
 * network whenever you call send. This makes network transparent games
 * very easy. You first have to register the data to a KGamePropertyHandler
 * using KGamePropertyBase::registerData (which is called by the
 * constructor). For the KGamePropertyHandler you can use
 * KGame::dataHandler or KPlayer::dataHandler but you can also create your
 * own data handler.
 *
 * There are several concepts you can follow when writing network games. These
 * concepts differ completely from the way how data is transferred so you should
 * decide which one to use. You can also mix these concepts for a single
 * property but we do not recommend this. The concepts:
 * <ul>
 * <li> Always Consistent (clean)
 * <li> Not Always Consistent (dirty)
 * <li> A Mixture (very dirty)
 * </ul>
 * I repeat: we do <em>not</em> recommend the third option ("a mixture"). Unless
 * you have a good reason for this you will probably introduce some hard to find
 * (and to fix) bugs.
 *
 * @section Always consistent (clean):
 *
 * This "policy" is default. Whenever you create a KGameProperty it is always
 * consistent. This means that consistency is the most important thing for the
 * property. This is achieved by using send to change the value of the
 * property. send needs a running KMessageServer and therefore
 * <em>MUST</em> be plugged into a KGamePropertyHandler using either
 * registerData or the constructor. The parent of the dataHandler must be able
 * to send messages (see above: the message server must be running). If you use
 * send to change the value of a property you won't see the effect
 * immediately: The new value is first transferred to the message server which
 * queues the message. As soon as <em>all</em> messages in the message server
 * which are before the changed property have been transferred the message
 * server delivers the new value of the KGameProperty to all clients. A
 * QTimer::singleShot is used to queue the messages inside the
 * KMessageServer.
 *
 * This means that if you do the following:
 * \code
 * KGamePropertyInt myProperty(id, dataHandler());
 * myProperty.initData(0);
 * myProperty = 10;
 * int value = myProperty.value();
 * \endcode
 * then "value" will be "0". initData is used to initialize the property
 * (e.g. when the KMessageServer is not yet running or can not yet be
 * reached). This is because "myProperty = 10" or "myProperty.send(10)" send a
 * message to the KMessageServer which uses QTimer::singleShot to
 * queue the message. The game first has to go back into the event loop where
 * the message is received. The KGamePropertyHandler receives the new value
 * sets the property. So if you need the new value you need to store it in a
 * different variable (see setLocal which creates one for you until the
 * message is received). The KGamePropertyHandler emits a signal (unless
 * you called setEmitSignal with false) when the new value is received:
 * KGamePropertyHandler::signalPropertyChanged. You can use this to react
 * to a changed property.
 *
 * This may look quite confusing but it has a <em>big</em> advantage: all
 * KGameProperty objects are ensured to have the same value on all clients in
 * the game at every time. This way you will save you a lot of trouble as
 * debugging can be very difficult if the value of a property changes
 * immediately on client A but only after one or two additional messages
 * (function calls, status changes, ...) on client B.
 *
 * The only disadvantage of this (clean) concept is that you cannot use a
 * changed variable immediately but have to wait for the KMessageServer to
 * change it. You probably want to use
 * KGamePropertyHandler::signalPropertyChanged for this.
 *
 * @section Not Always Consistent (dirty):
 *
 * There are a lot of people who don't want to use the (sometimes quite complex)
 * "clean" way. You can use setAlwaysConsistent to change the default
 * behaviour of the KGameProperty. If a property is not always consistent
 * it will use changeValue to send the property.  changeValue also uses
 * send to send the new value over network but it also uses
 * setLocal to create a local copy of the property. This copy is created
 * dynamically and is deleted again as soon as the next message from the network
 * is received. To use the example above again:
 * \code
 * KGamePropertyInt myProperty(id, dataHandler());
 * myProperty.setAlwaysConsistent(false);
 * myProperty.initData(0);
 * myProperty = 10;
 * int value = myProperty.value();
 * \endcode
 * Now this example will "work" so value now is 10. Additionally the
 * KMessageServer receives a message from the local client (just as explained
 * above in "Always Consistent"). As soon as the message returns to the local
 * client again the local value is deleted, as the "network value" has the same
 * value as the local one. So you won't lose the ability to use the always
 * consistent "clean" value of the property if you use the "dirty" way. Just use
 * networkValue to access the value which is consistent among all clients.
 *
 * The advantage of this concept is clear: you can use a KGameProperty as
 * every other variable as the changes value takes immediate effect.
 * Additionally you can be sure that the value is transferred to all clients.
 * You will usually not experience serious bugs just because you use the "dirty"
 * way. Several events have to happen at once to get these "strange errors"
 * which result in inconsistent properties (like "game running" on client A but
 * "game ended/paused" on client B).  But note that there is a very good reason
 * for the existence of these different concepts of KGameProperty. I have
 * myself experienced such a "strange error" and it took me several days to find
 * the reason until I could fix it. So I personally recommend the "clean" way.
 * On the other hand if you want to port a non-network game to a network game
 * you will probably start with "dirty" properties as it is you will not have to
 * change that much code...
 *
 * @section A Mixture (very dirty):
 *
 * You can also mix the concepts above. Note that we really don't recommend
 * this. With a mixture I mean something like this:
 * \code
 * KGamePropertyInt myProperty(id, dataHandler());
 * myProperty.setAlwaysConsistent(false);
 * myProperty.initData(0);
 * myProperty = 10;
 * myProperty.setAlwaysConsistent(true);
 * myProperty = 20;
 * \endcode
 * (totally senseless example, btw) I.e. I am speaking of mixing both concepts
 * for a single property. Things like
 * \code
 * KGamePropertyInt myProperty1(id1, dataHandler());
 * KGamePropertyInt myProperty2(id2, dataHandler());
 * myProperty1.initData(0);
 * myProperty2.initData(0);
 * myProperty1.setAlwaysConsistent(false);
 * myProperty2.setAlwaysConsistent(true);
 * myProperty1 = 10;
 * myProperty2 = 20;
 * \endcode
 * are ok. But mixing the concepts for a single property will make it nearly
 * impossible to you to debug your game.
 *
 * So the right thing to do(tm) is to decide in the constructor whether you want
 * a "clean" or "dirty" property.
 *
 * Even if you have decided for one of the concepts you still can manually
 * follow another concept than the "policy" of your property. So if you use an
 * always consistent KGameProperty you still can manually call
 * changeValue as if it was not always consistent. Note that although this is
 * also kind of a "mixture" as described above this is very useful sometimes. In
 * contrast to the "mixture" above you don't have the problem that you don't
 * exactly know which concept you are currently following because you used the
 * function of the other concept only once.
 *
 * @section Custom classes:
 *
 * If you want to use a custom class with KGameProperty you have to implement the
 * operators << and >> for QDataStream:
 * \code
 * class Card
 * {
 * public:
 * int type;
 * int suite;
 * };
 * QDataStream& operator<<(QDataStream& stream, Card& card)
 * {
 * qint16 type = card.type;
 * qint16 suite = card.suite;
 * s << type;
 * s << suite;
 * return s;
 * }
 * QDataStream& operator>>(QDataStream& stream, Card& card)
 * {
 * qint16 type;
 * qint16 suite;
 * s >> type;
 * s >> suite;
 * card.type = (int)type;
 * card.suite = (int)suite;
 * return s;
 * }
 *
 * class Player : KPlayer
 * {
 * [...]
 * KGameProperty<Card> mCards;
 * };
 * \endcode
 *
 * Note: unlike most QT classes KGameProperty objects are *not* deleted
 * automatically! So if you create an object using e.g. KGameProperty<int>* data =
 * new KGameProperty(id, dataHandler()) you have to put a delete data into your
 * destructor!
 *
 * @author Andreas Beckermann <[email protected]>
 **/
template<class type>
class KGameProperty  : public KGamePropertyBase
{
public:
    /**
     * Constructs a KGameProperty object. A KGameProperty object will transmit
     * any changes to the KMessageServer and then to all clients in the
     * game (including the one that has sent the new value)
     * @param id The id of this property. <em>MUST be UNIQUE</em>! Used to send and
     * receive changes in the property of the playere automatically via
     * network.
     * @param owner The parent of the object. Must be a KGame which manages
     * the changes made to this object, i.e. which will send the new data.
     * Note that in contrast to most KDE/QT classes KGameProperty objects
     * are <em>not</em> deleted automatically!
     **/
// TODO: ID: Very ugly - better use something like parent()->propertyId() or so which assigns a free id automatically.
    KGameProperty(int id, KGamePropertyHandler* owner) : KGamePropertyBase(id, owner) { init(); }
 
    /**
     * This constructor does nothing. You have to call
     * KGamePropertyBase::registerData
     * yourself before using the KGameProperty object.
     **/
    KGameProperty() : KGamePropertyBase() { init(); }
 
    ~KGameProperty() override {}
 
    /**
     * Set the value depending on the current policy (see
     * setConsistent). By default KGameProperty just uses send to set
     * the value of a property. This behaviour can be changed by using
     * setConsistent.
     * @param v The new value of the property
     **/
    void setValue(type v)
    {
        switch (policy()) {
            case PolicyClean:
                send(v);
                break;
            case PolicyDirty:
                changeValue(v);
                break;
            case PolicyLocal:
                setLocal(v);
                break;
            default: // NEVER!
                qCritical() << "Undefined Policy in property" << id();
                return;
        }
    }
 
 
    /**
     * This function sends a new value over network.
     *
     * Note that the value DOES NOT change when you call this function. This
     * function saves the value into a QDataStream and calls
     * sendProperty where it gets forwarded to the owner and finally the
     * value is sent over network. The KMessageServer now sends the
     * value to ALL clients - even the one who called this function. As soon
     * as the value from the message server is received load is called
     * and _then_ the value of the KGameProperty has been set.
     *
     * This ensures that a KGameProperty has _always_ the same value on
     * _every_ client in the network. Note that this means you can NOT do
     * something like
     * \code
     * myProperty.send(1);
     * doSomething(myProperty);
     * \endcode
     * as myProperty has not yet been set when doSomething is being called.
     *
     * You are informed about a value change by a signal from the parent of
     * the property which can be deactivated by setEmittingSignal because of
     * performance (you probably don't have to deactivate it - except you
     * want to write a real-time game like Command&Conquer with a lot of
     * activity). See emitSignal
     *
     * Note that if there is no KMessageServer accessible - before
     * the property has been registered to the KGamePropertyHandler (as
     * it is the case e.g. before a KPlayer has been plugged into the
     * KGame object) the property is *not* sent but set *locally* (see
     * setLocal)!
     *
     * @param v The new value of the property
     * @return whether the property could be sent successfully
     * @see setValue setLocal changeValue value
     **/
    bool send(type v)
    {
        if (isOptimized() && mData == v) {
            return true;
        }
        if (isLocked()) {
            return false;
        }
        QByteArray b;
        QDataStream stream(&b, QIODevice::WriteOnly);
        stream << v;
        if (!sendProperty(b)) {
            setLocal(v);
            return false;
        }
        return true;
    }
 
    /**
     * This function sets the value of the property directly, i.e. it
     * doesn't send it to the network.
     *
     * Int contrast to @see you change _only_ the local value when using
     * this function. You do _not_ change the value of any other client. You
     * probably don't want to use this if you are using a dedicated server
     * (which is the only "client" which is allowed to change a value) but
     * rather want to use send().
     *
     * But if you use your clients as servers (i.e. all clients receive a
     * players turn and then calculate the reaction of the game theirselves)
     * then you probably want to use setLocal as you can do things like
     * \code
     * myProperty.setLocal(1);
     * doSomething(myProperty);
     * \endcode
     * on every client.
     *
     * If you want to set the value locally AND send it over network you
     * want to call changeValue!
     *
     * You can also use setPolicy to set the default policy to
     * PolicyLocal.
     *
     * @see setValue send changeValue value
     **/
    bool setLocal(type v)
    {
        if (isOptimized() && mData == v) {
            return false;
        }
        if (isLocked()) {
            return false;
        }
        mData = v;
        setDirty(true);
        if (isEmittingSignal()) {
            emitSignal();
        }
        return true;
    }
 
    /**
     * This function does both, change the local value and change the
     * network value. The value is sent over network first, then changed
     * locally.
     *
     * This function is a convenience function and just calls send
     * followed by setLocal
     *
     * Note that emitSignal is also called twice: once after
     * setLocal and once when the value from send is received
     *
     * @see send setLocal setValue value
     **/
    void changeValue(type v)
    {
        send(v);
        setLocal(v);
    }
 
    /**
     * Saves the object to a stream.
     * @param stream The stream to save to
     **/
    void save(QDataStream &stream) override
    {
        stream << mData;
    }
 
    /**
     * @return The local value (see setLocal) if it is existing,
     * otherwise the network value which is always consistent on every
     * client.
     **/
    const type& value() const
    {
        return mData;
    }
 
    /**
     * Reads from a stream and assigns the read value to this object.
     *
     * This function is called automatically when a new value is received
     * over network (i.e. it has been sent using send on this or any
     * other client) or when a game is loaded (and maybe on some other
     * events).
     *
     * Also calls emitSignal if isEmittingSignal is TRUE.
     * @param s The stream to read from
     **/
    void load(QDataStream& s) override
    {
        s >> mData;
        setDirty(false);
        if (isEmittingSignal()) {
            emitSignal();
        }
    }
 
    /**
     * This calls setValue to change the value of the property. Note
     * that depending on the policy (see setAlwaysConsistent) the
     * returned value might be different from the assigned value!!
     *
     * So if you use setPolicy(PolicyClean):
     * \code
     * int a, b = 10;
     * myProperty = b;
     * a = myProperty.value();
     * \endcode
     * Here a and b would differ!
     * The value is actually set as soon as it is received from the
     * KMessageServer which forwards it to ALL clients in the network.
     *
     * If you use a clean policy (see setPolicy) then
     * the returned value is the assigned value
     **/
    const type& operator=(const type& t)
    {
        setValue(t);
        return value();
    }
 
    /**
     * This copies the data of property to the KGameProperty object.
     *
     * Equivalent to setValue(property.value());
     **/
    const type& operator=(const KGameProperty& property)
    {
        setValue(property.value());
        return value();
    }
 
    /**
     * Yeah, you can do it!
     * \code
     *  int a = myGamePropertyInt;
     * \endcode
     * If you don't see it: you don't have to use integerData.value()
     **/
    operator type() const { return value(); }
 
    const type_info* typeinfo() override { return &typeid(type); }
 
private:
    void init() { }
 
private:
    type mData;
};
 
 
typedef KGameProperty<int>   KGamePropertyInt;
typedef KGameProperty<unsigned int>   KGamePropertyUInt;
typedef KGameProperty<QString>   KGamePropertyQString;
typedef KGameProperty<qint8>   KGamePropertyBool;
 
#endif