QtPlugin: duplicate if-conditions in generated qt_metacast

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My problem is the following: I have written a plugin that inherits several interfaces. My plugin definition is:

class Info: public QObject, CoreInterface, DataInterface {
    Q_OBJECT
#if QT_VERSION >= 0x050000
    Q_PLUGIN_METADATA(IID "Plugins.Info")
#endif
    Q_INTERFACES(CoreInterface DataInterface)

public:
    void setValue(const QString &role, QVariant value, QByteArray &codogram) const override;
    int protocol() const override;
    int type() const override;
    int size() const override;
    QVariant value(const QString &role, const QByteArray &codogram) const override;
    QByteArray create() const override;
    QStringList roles() const override;
};

where CoreInterface and DataInterafce are declared interfaces.
I have checked my project with PVS and found that generated MOC files contains the following code:

void *Info::qt_metacast(const char *_clname)
{
    if (!_clname) return nullptr;
    if (!strcmp(_clname, qt_meta_stringdata_Info.stringdata0))
        return static_cast<void*>(this);
    if (!strcmp(_clname, "CoreInterface"))
        return static_cast< CoreInterface*>(this);
    if (!strcmp(_clname, "DataInterface"))
        return static_cast< DataInterface*>(this);
    if (!strcmp(_clname, "CoreInterface"))
        return static_cast< CoreInterface*>(this);
    if (!strcmp(_clname, "DataInterface"))
        return static_cast< DataInterface*>(this);
    return QObject::qt_metacast(_clname);
}

So each interface name is being checked twice for casting. What is the reason for this?

[SGaist]

Hi,

Can you also provide your interfaces definition ?
What version of Qt are you using ?

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@SGaist Sure I can
I have checked it on Qt 5.11.1 and Qt 4.8.6

class CoreInterface {
public:
    virtual int protocol() const = 0;
};
Q_DECLARE_INTERFACE(CoreInterface, "CoreInterface")

class DataInterface {
public:
    virtual void setValue(const QString &role, QVariant value, QByteArray &codogram) const = 0;
    virtual int type() const = 0;
    virtual int size() const = 0;
    virtual QVariant value(const QString &role, const QByteArray &codogram) const = 0;
    virtual QByteArray create() const = 0;
    virtual QStringList roles() const = 0;
};
Q_DECLARE_INTERFACE(DataInterface, "DataInterface")

[SGaist]

That's because you are not using Q_DECLARE_INTERFACE correctly. Therefor you are creating the duplicate entries.

See the identifier format in the macro documentation.

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@SGaist Well, according to documentation the only thing I should keep in mind is that identifier must be unique, and I haven't broke it. There is nothing about identifier and classname should not match literaly, and that is the reason of my problem as far as I can see. Maybe there is a point to specify that in docs.

[SGaist]

Well, a class name is not a unique identifier since it's already used to name said class.