GWorld = LoadedWorld;    //特征
if (!LoadedWorld->bIsWorldInitialized)
{
    LoadedWorld->InitWorld();
}
bWorldChanged = true;
// Track session change on seamless travel.
NETWORK_PROFILER(GNetworkProfiler.TrackSessionChange(true, LoadedWorld->URL));
checkSlow((LoadedWorld->GetNetMode() == NM_Client) == bIsClient);
if (bCreateNewGameMode)
{
    LoadedWorld->SetGameMode(PendingTravelURL);
}
// if we've already switched to entry before and this is the transition to the new map, re-create the gameinfo
if (bSwitchedToDefaultMap && !bIsClient)
{
    if (FAudioDevice* AudioDevice = LoadedWorld->GetAudioDeviceRaw())
    {
        AudioDevice->SetDefaultBaseSoundMix(LoadedWorld->GetWorldSettings()->DefaultBaseSoundMix);
    }
    // Copy cheat flags if the game info is present
    // @todo UE4 FIXMELH - see if this exists, it should not since it's created in GameMode or it's garbage info
    if (LoadedWorld->NetworkManager != nullptr)
    {
        LoadedWorld->NetworkManager->bHasStandbyCheatTriggered = bHasStandbyCheatTriggered;
    }
}
// Make sure "always loaded" sub-levels are fully loaded
{
    SCOPE_LOG_TIME_IN_SECONDS(TEXT("    SeamlessTravel FlushLevelStreaming "), nullptr)  //特征
    LoadedWorld->FlushLevelStreaming(EFlushLevelStreamingType::Visibility);    
}

class Object
{
public:
    virtual string ToString() = 0;
};
class ClassA :public Object
{
public:
    virtual string ToString(){ return "MyClass"; }
};
class ClassB :public Object
{
public:
    virtual string ToString(){ return "MyClass"; }
};
Object* FactoryCreat(const string& className)
{
    if (className == "ClassA")
        return new ClassA;
    else if (className == "ClassB")
        return new ClassB;
    ...
}
int main()
{
    Object* obj = FactoryCreat("ClassA");
    cout << obj->ToString();
    delete obj;
    return 0;
}