can't compare lists of my struct

mzimmers

Hi all -

This is what I'm trying to do:

struct ValveConfiguration : public QObject {
    Q_OBJECT

    QUuid uuid;
    bool on;
    bool operator == (const ValveConfiguration &rhs) const {
        if (uuid == rhs.uuid && on == rhs.on)
            return true;
        return false;
    }
    bool operator != (const ValveConfiguration &rhs) const { return !(*this == rhs); }
};

class Outcome : public QObject
{
    Q_OBJECT
    QList<ValveConfiguration> m_valveConfigurationList;
    bool setValveConfigurationList(const QList<ValveConfiguration> &list)
    {
        if (m_valveConfigurationList != list) { // getting an error here.
        ....

I'm getting the following error:

outcome.cpp:55:34: Invalid operands to binary expression ('QList<ValveConfiguration>' and 'const QList<ValveConfiguration>')
qlist.h:333:56: candidate template ignored: requirement 'std::conjunction_v<std::disjunction<std::is_base_of<QList<ValveConfiguration>, ValveConfiguration>, QTypeTraits::has_operator_equal<ValveConfiguration>>>' was not satisfied [with U = ValveConfiguration]

Can someone tell me what I'm doing wrong here? (The == operator fails, too.)

Thanks...

Christian Ehrlicher

@mzimmers said in can't compare lists of my struct:

QList<ValveConfiguration>

You can't copy objects derived from QObject so you won't be able to add anything to this container.

JonB

@mzimmers
...And further to @Christian-Ehrlicher, before you ask it is more usual to create lists of pointers to QObjects, QList<ValveConfiguration *>, which you can compare/copy....

sierdzio

Also, inside of Q_OBJECT macro, there is a private: section, so anything you type after Q_OBJECT is private. You need to make it public:

Q_OBJECT

public:
QUuid uuid;
    bool on;
    bool operator == (const ValveConfiguration &rhs) const {
        if (uuid == rhs.uuid && on == rhs.on)
            return true;
        return false;
    }
    bool operator != (const ValveConfiguration &rhs) const { return !(*this == rhs); }

Pl45m4

@sierdzio said in can't compare lists of my struct:

Also, inside of Q_OBJECT macro, there is a private: section, so anything you type after Q_OBJECT is private

Since Q_OBJECT extends to

#define Q_OBJECT \
public: \
    QT_WARNING_PUSH \
    Q_OBJECT_NO_OVERRIDE_WARNING \
    static const QMetaObject staticMetaObject; \
    virtual const QMetaObject *metaObject() const; \
    virtual void *qt_metacast(const char *); \
    virtual int qt_metacall(QMetaObject::Call, int, void **); \
    QT_TR_FUNCTIONS \
private: \
    Q_OBJECT_NO_ATTRIBUTES_WARNING \
    Q_DECL_HIDDEN_STATIC_METACALL static void qt_static_metacall(QObject *, QMetaObject::Call, int, void **); \
    QT_WARNING_POP \
    struct QPrivateSignal { explicit QPrivateSignal() = default; }; \
    QT_ANNOTATE_CLASS(qt_qobject, "")

and you usually use Q_OBJECT at the top of your class declaration.
If you would switch the private: and public: section from the #define Q_OBJECT, which I initially thought would be a good idea, it would violate the C++ "standard" (common sense), because no access specifier in a C++ class means private:.

Then, @mzimmers ' code would work as expected but you would ask yourself why :)
I doubt people look at the Q_OBJECT code every day :)

mzimmers

Thanks for all the information, guys. Originally, I had declared the struct without deriving from QObject, and that didn't work, but I removed the QObject derivation, and now it seems to work.

JonB

@mzimmers Well, yes, because as @Christian-Ehrlicher said

You can't copy objects derived from QObject

So removing QObject from inherited class(es) will allow copying and your code to work. If you ever want to put QObject in again you'll have work with a list of pointers, QList<QObject *>.

Pl45m4

@mzimmers said in can't compare lists of my struct:

I removed the QObject derivation, and now it seems to work.

If you don't plan to ever use meta-object related stuff, then you really don't need a QObject derived class or the Q_OBJECT macro (for metacalls / qt signals).