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Recurring C++ and Qt anti-patterns

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  • fcarneyF Offline
    fcarneyF Offline
    fcarney
    wrote on last edited by
    #100

    Be careful with not doing things the pythonic way in python. A lot of the time doing it the pythonic way leverages the internals of the language. In other words it pushes the execution from the interpreter to the built in methods that are written in C. So it can have an effect on performance. I don't think the exception example does this though. There may be other reasons I am not aware of.

    C++ is a perfectly valid school of magic.

    1 Reply Last reply
    1
    • Kent-DorfmanK Offline
      Kent-DorfmanK Offline
      Kent-Dorfman
      wrote on last edited by
      #101

      wait a cotton pickin minute! there is no explicit cast to double in python so the x/double(0) argument is invalid on that basis alone...and x/float(0) behaves as expected.

      1 Reply Last reply
      0
      • fcarneyF Offline
        fcarneyF Offline
        fcarney
        wrote on last edited by
        #102

        Uncomfortable admission:
        I wrote windows specfic code today...

        C++ is a perfectly valid school of magic.

        sierdzioS 1 Reply Last reply
        3
        • fcarneyF fcarney

          Uncomfortable admission:
          I wrote windows specfic code today...

          sierdzioS Offline
          sierdzioS Offline
          sierdzio
          Moderators
          wrote on last edited by
          #103

          @fcarney said in Recurring C++ and Qt anti-patterns:

          Uncomfortable admission:
          I wrote windows specfic code today...

          We feel for you :D

          (Z(:^

          1 Reply Last reply
          2
          • fcarneyF Offline
            fcarneyF Offline
            fcarney
            wrote on last edited by
            #104

            Here is a nice QML anti-pattern:

            Column {
                Rectangle {
                    height: parent.height
                }
            }
            

            This one was "fun". Yeah, it doesn't necessarily detect the loop and it locks up the desktop (Gnome). So you have to kill the process manually from a terminal outside of the desktop (ctrl-alt-f4).

            C++ is a perfectly valid school of magic.

            ODБOïO 1 Reply Last reply
            0
            • fcarneyF fcarney

              Here is a nice QML anti-pattern:

              Column {
                  Rectangle {
                      height: parent.height
                  }
              }
              

              This one was "fun". Yeah, it doesn't necessarily detect the loop and it locks up the desktop (Gnome). So you have to kill the process manually from a terminal outside of the desktop (ctrl-alt-f4).

              ODБOïO Offline
              ODБOïO Offline
              ODБOï
              wrote on last edited by
              #105

              @fcarney said in Recurring C++ and Qt anti-patterns:

              Gnome

              this code works properly on windows with Qt_5_14_0_MinGW_64_bit

              1 Reply Last reply
              0
              • JonBJ Online
                JonBJ Online
                JonB
                wrote on last edited by
                #106

                From https://forum.qt.io/topic/113223/check-whether-a-script-exists-by-script-name/14

                QProcess process;
                process.setStandardOutputFile(QProcess::nullDevice());
                if (!process.startDetached(progName, args))
                ...
                

                Would anyone care to comment on why C++ allows calling a static method off an instance without (seemingly) offering the option of a warning message for it? :) (C# doesn't let me write this.)

                kshegunovK 1 Reply Last reply
                0
                • SGaistS Offline
                  SGaistS Offline
                  SGaist
                  Lifetime Qt Champion
                  wrote on last edited by
                  #107

                  AFAIK, there's nothing wrong with that. It's just that in the case you are showing, the static method has a specific behaviour that makes it unsuitable to be called like that.

                  Interested in AI ? www.idiap.ch
                  Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

                  1 Reply Last reply
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                  • JonBJ JonB

                    From https://forum.qt.io/topic/113223/check-whether-a-script-exists-by-script-name/14

                    QProcess process;
                    process.setStandardOutputFile(QProcess::nullDevice());
                    if (!process.startDetached(progName, args))
                    ...
                    

                    Would anyone care to comment on why C++ allows calling a static method off an instance without (seemingly) offering the option of a warning message for it? :) (C# doesn't let me write this.)

                    kshegunovK Offline
                    kshegunovK Offline
                    kshegunov
                    Moderators
                    wrote on last edited by kshegunov
                    #108

                    @JonB said in Recurring C++ and Qt anti-patterns:

                    Would anyone care to comment on why C++ allows calling a static method off an instance without (seemingly) offering the option of a warning message for it? :) (C# doesn't let me write this.)

                    Because the class is known and that's all that matters. Whether you call it through an object or with its qualified name makes no difference. Actually, there's one widespread use of that in the Qt documentation:

                    int main(int argc, char *argv[])
                    {
                        QApplication app(argc, argv);
                        return app.exec(); // QCoreApplication::exec is static
                    }
                    

                    Read and abide by the Qt Code of Conduct

                    JonBJ 1 Reply Last reply
                    2
                    • kshegunovK kshegunov

                      @JonB said in Recurring C++ and Qt anti-patterns:

                      Would anyone care to comment on why C++ allows calling a static method off an instance without (seemingly) offering the option of a warning message for it? :) (C# doesn't let me write this.)

                      Because the class is known and that's all that matters. Whether you call it through an object or with its qualified name makes no difference. Actually, there's one widespread use of that in the Qt documentation:

                      int main(int argc, char *argv[])
                      {
                          QApplication app(argc, argv);
                          return app.exec(); // QCoreApplication::exec is static
                      }
                      
                      JonBJ Online
                      JonBJ Online
                      JonB
                      wrote on last edited by JonB
                      #109

                      @kshegunov
                      But that is not my point/question. Which is: this piece of code is not the first (or the last) where someone has mistakenly written this. If C++ wants it this way, would it not be a good idea by now for compilers to offer a warning option? There is reason that e.g. C# does not allow it.

                      kshegunovK 1 Reply Last reply
                      0
                      • fcarneyF Offline
                        fcarneyF Offline
                        fcarney
                        wrote on last edited by
                        #110

                        "Within C++, there is a much smaller and cleaner language struggling to get out."
                        ...
                        "And no, that smaller and cleaner language is not Java or C#."
                        Bjarne Stroustrup

                        C++ is a perfectly valid school of magic.

                        1 Reply Last reply
                        0
                        • JonBJ JonB

                          @kshegunov
                          But that is not my point/question. Which is: this piece of code is not the first (or the last) where someone has mistakenly written this. If C++ wants it this way, would it not be a good idea by now for compilers to offer a warning option? There is reason that e.g. C# does not allow it.

                          kshegunovK Offline
                          kshegunovK Offline
                          kshegunov
                          Moderators
                          wrote on last edited by
                          #111

                          @JonB said in Recurring C++ and Qt anti-patterns:

                          If C++ wants it this way, would it not be a good idea by now for compilers to offer a warning option?

                          If this were a potential error, probably. Since this is almost always safe there's no reason to offer a warning.

                          There is reason that e.g. C# does not allow it.

                          Which is what exactly?

                          Read and abide by the Qt Code of Conduct

                          jsulmJ 1 Reply Last reply
                          0
                          • kshegunovK kshegunov

                            @JonB said in Recurring C++ and Qt anti-patterns:

                            If C++ wants it this way, would it not be a good idea by now for compilers to offer a warning option?

                            If this were a potential error, probably. Since this is almost always safe there's no reason to offer a warning.

                            There is reason that e.g. C# does not allow it.

                            Which is what exactly?

                            jsulmJ Offline
                            jsulmJ Offline
                            jsulm
                            Lifetime Qt Champion
                            wrote on last edited by
                            #112

                            @kshegunov I think the point from @JonB is that people do call static methods on an object by mistake and then wander why the object is not changed (I sometimes see this here in the forums). The compiler could generate a warning, but I doubt people would care enough about those if they do not even notice what they do wrongly :-)

                            https://forum.qt.io/topic/113070/qt-code-of-conduct

                            J.HilkJ kshegunovK 2 Replies Last reply
                            1
                            • jsulmJ jsulm

                              @kshegunov I think the point from @JonB is that people do call static methods on an object by mistake and then wander why the object is not changed (I sometimes see this here in the forums). The compiler could generate a warning, but I doubt people would care enough about those if they do not even notice what they do wrongly :-)

                              J.HilkJ Offline
                              J.HilkJ Offline
                              J.Hilk
                              Moderators
                              wrote on last edited by
                              #113

                              @jsulm said in Recurring C++ and Qt anti-patterns:

                              but I doubt people would care enough about those

                              They don't I have taken over projects that hat on first compile 20k + warnings...

                              "Every time you compile with warnings, a fairy dies! So don't forget to clap your hands during compile time. Once for each fairy!"


                              Be aware of the Qt Code of Conduct, when posting : https://forum.qt.io/topic/113070/qt-code-of-conduct


                              Q: What's that?
                              A: It's blue light.
                              Q: What does it do?
                              A: It turns blue.

                              1 Reply Last reply
                              0
                              • jsulmJ jsulm

                                @kshegunov I think the point from @JonB is that people do call static methods on an object by mistake and then wander why the object is not changed (I sometimes see this here in the forums). The compiler could generate a warning, but I doubt people would care enough about those if they do not even notice what they do wrongly :-)

                                kshegunovK Offline
                                kshegunovK Offline
                                kshegunov
                                Moderators
                                wrote on last edited by kshegunov
                                #114

                                @jsulm said in Recurring C++ and Qt anti-patterns:

                                @kshegunov I think the point from @JonB is that people do call static methods on an object by mistake and then wander why the object is not changed (I sometimes see this here in the forums).

                                Yes, I acknowledged that, but it's not an error, nor does it warrant a warning in my mind. One just have to know what they're doing/expecting of said method, which is good approach in every case. ;)

                                The compiler could generate a warning, but I doubt people would care enough about those if they do not even notice what they do wrongly :-)

                                That's why I compile with warnings-are-errors before I even consider deploying. The other option is just abysmal ... and can be dangerous depending on which field you're working in. So to everyone out there that ignores warnings: fix your freaking code!

                                Read and abide by the Qt Code of Conduct

                                JonBJ 1 Reply Last reply
                                0
                                • kshegunovK kshegunov

                                  @jsulm said in Recurring C++ and Qt anti-patterns:

                                  @kshegunov I think the point from @JonB is that people do call static methods on an object by mistake and then wander why the object is not changed (I sometimes see this here in the forums).

                                  Yes, I acknowledged that, but it's not an error, nor does it warrant a warning in my mind. One just have to know what they're doing/expecting of said method, which is good approach in every case. ;)

                                  The compiler could generate a warning, but I doubt people would care enough about those if they do not even notice what they do wrongly :-)

                                  That's why I compile with warnings-are-errors before I even consider deploying. The other option is just abysmal ... and can be dangerous depending on which field you're working in. So to everyone out there that ignores warnings: fix your freaking code!

                                  JonBJ Online
                                  JonBJ Online
                                  JonB
                                  wrote on last edited by
                                  #115

                                  @kshegunov
                                  I'll try to keep my remarks brief, as I don't want to dominate this thread.

                                  As @jsulm said, my point is that being allowed to call a static method on an instance is not wrong or an error, but it may indicate a programmer mistake. I observe this empirically from the number of cases I have seen, such as the one I quoted from this forum.

                                  If I write a statement like word;, then gcc gives me a -Wunused-value warning. If I write if (word = value) I get a -Wparentheses warning. Neither of these is "wrong", the second one in particular is perfectly useful, yet someone recognised they may indicate commonly made faux-pas. Which the user may ignore, or suppress, at their peril. Personally, I would have liked to have seen a -Wstatic-call-on-instance :)

                                  kshegunovK 1 Reply Last reply
                                  0
                                  • JonBJ JonB

                                    @kshegunov
                                    I'll try to keep my remarks brief, as I don't want to dominate this thread.

                                    As @jsulm said, my point is that being allowed to call a static method on an instance is not wrong or an error, but it may indicate a programmer mistake. I observe this empirically from the number of cases I have seen, such as the one I quoted from this forum.

                                    If I write a statement like word;, then gcc gives me a -Wunused-value warning. If I write if (word = value) I get a -Wparentheses warning. Neither of these is "wrong", the second one in particular is perfectly useful, yet someone recognised they may indicate commonly made faux-pas. Which the user may ignore, or suppress, at their peril. Personally, I would have liked to have seen a -Wstatic-call-on-instance :)

                                    kshegunovK Offline
                                    kshegunovK Offline
                                    kshegunov
                                    Moderators
                                    wrote on last edited by
                                    #116

                                    Yes, yes, I get that. Then you better start getting used to writing code like this:

                                    int main(int argc, char *argv[])
                                    {
                                        QApplication app(argc, argv);
                                        (void) app; // or Q_UNUSED(app);
                                    
                                        return QApplication::exec();
                                    }
                                    

                                    Because an unused variable is actually a warning ... and yes in the general case the compiler can't strip it directly, because constructors and/or destructors may have side effects (if they're out-of-line, which they often are). So on the off chance of that, calling a static method on an object is much more benign is my argument. It's a logical error that you'd be able to debug quite easily, and not propagate it into the program runtime. I get people can and will fall for it from time to time, but again, it's rather benign. I'd rather see more strict warnings for implicit conversions than for this ...

                                    Read and abide by the Qt Code of Conduct

                                    JonBJ 1 Reply Last reply
                                    0
                                    • kshegunovK kshegunov

                                      Yes, yes, I get that. Then you better start getting used to writing code like this:

                                      int main(int argc, char *argv[])
                                      {
                                          QApplication app(argc, argv);
                                          (void) app; // or Q_UNUSED(app);
                                      
                                          return QApplication::exec();
                                      }
                                      

                                      Because an unused variable is actually a warning ... and yes in the general case the compiler can't strip it directly, because constructors and/or destructors may have side effects (if they're out-of-line, which they often are). So on the off chance of that, calling a static method on an object is much more benign is my argument. It's a logical error that you'd be able to debug quite easily, and not propagate it into the program runtime. I get people can and will fall for it from time to time, but again, it's rather benign. I'd rather see more strict warnings for implicit conversions than for this ...

                                      JonBJ Online
                                      JonBJ Online
                                      JonB
                                      wrote on last edited by JonB
                                      #117

                                      @kshegunov
                                      I wish I hadn't picked the "unused variable" warning example :) Please look at the "parentheses" warning instead to compare against.

                                      calling a static method on an object is much more benign [...] that you'd be able to debug quite easily

                                      Then we shouldn't see too many questions about this from ppl :)

                                      P.S.
                                      I have always written:

                                      QApplication app(argc, argv);
                                      return app.exec();
                                      

                                      I had never even noticed QApplication::exec() is static, I presumed it was instance. Although it does no harm, I dislike this even more now...!

                                      1 Reply Last reply
                                      1
                                      • kshegunovK Offline
                                        kshegunovK Offline
                                        kshegunov
                                        Moderators
                                        wrote on last edited by kshegunov
                                        #118

                                        Here's one a bit more convoluted, by yours truly:

                                        GraphDialog::GraphDialog(QWidget * parent)
                                            : QDialog(parent), chartsModel(&graphMeta)
                                        {
                                            // ...
                                            QObject::connect(ui.chartsView->selectionModel(), &QItemSelectionModel::currentChanged, [this] (const QModelIndex & current) -> void  {
                                                ui.chartEdit->setChart(current.isValid() ? &graphMeta.charts[current.row()] : nullptr);
                                            });
                                            QObject::connect(ui.createChartButton, &QPushButton::clicked, &chartsModel, &RbMeta::ChartsModel::addChart);
                                            // ...
                                        }
                                        

                                        where chartsModel is editable (basically an adapter on top of graphMeta) and my types are POD, graphMeta.charts is QVector .

                                        I'm curious whether someone spots it (and no it's not immediately evident, I still haven't hit it, but it's there).

                                        Read and abide by the Qt Code of Conduct

                                        kshegunovK 1 Reply Last reply
                                        0
                                        • kshegunovK kshegunov

                                          Here's one a bit more convoluted, by yours truly:

                                          GraphDialog::GraphDialog(QWidget * parent)
                                              : QDialog(parent), chartsModel(&graphMeta)
                                          {
                                              // ...
                                              QObject::connect(ui.chartsView->selectionModel(), &QItemSelectionModel::currentChanged, [this] (const QModelIndex & current) -> void  {
                                                  ui.chartEdit->setChart(current.isValid() ? &graphMeta.charts[current.row()] : nullptr);
                                              });
                                              QObject::connect(ui.createChartButton, &QPushButton::clicked, &chartsModel, &RbMeta::ChartsModel::addChart);
                                              // ...
                                          }
                                          

                                          where chartsModel is editable (basically an adapter on top of graphMeta) and my types are POD, graphMeta.charts is QVector .

                                          I'm curious whether someone spots it (and no it's not immediately evident, I still haven't hit it, but it's there).

                                          kshegunovK Offline
                                          kshegunovK Offline
                                          kshegunov
                                          Moderators
                                          wrote on last edited by
                                          #119

                                          @kshegunov said in Recurring C++ and Qt anti-patterns:

                                          I'm curious whether someone spots it (and no it's not immediately evident, I still haven't hit it, but it's there).

                                          Well apparently not. I'll tell for funsies:

                                          &graphMeta.charts[current.row()]
                                          

                                          Passing a vector element by address is a recipe for disaster when the vector regrows in RbMeta::ChartsModel::addChart (where chartsModel(&graphMeta) is relevant here, again passing by reference in the initializer).

                                          Read and abide by the Qt Code of Conduct

                                          1 Reply Last reply
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