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Q_DECLARE_METATYPE for template class

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  • S Offline
    S Offline
    silicomancer
    wrote on last edited by
    #5

    Yes, I checked the "Type is not registered" error. It definitely corresponds to the missing container declaration.

    BTW that Container and ContainerBase class is not a QList or QSet or something. I should have mentioned that these are custom classes holding a single data instance. They are not similar to the Qt container.

    I did some tests. This one works too (however this isn't what I want to do):

    @Q_DECLARE_METATYPE(Container<ConcreteType>) @

    I also tried to declare the contained type first before declaring the container:

    @Q_DECLARE_METATYPE(ConcreteType)
    Q_DECLARE_METATYPE_TEMPLATE_1ARG(Container); @

    This gives me a different error "value_type is not an element of Container<T>" in this line of qmetatype.h:

    @template<typename T, bool = QMetaTypeId2<typename T::value_type>::Defined> @

    Then I added

    @typedef T value_type; @

    to my Container class. Now I get an error about a missing iterator.

    My impressions is that there are lot of concrete features that are expected being implemented in the provided container class. I can't fulfil all of them (especially iterators). Is that macro specialized for Qt containers and alike?

    Any ideas on this?

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    • N Offline
      N Offline
      NicuPopescu
      wrote on last edited by
      #6

      how I tested here:

      in simple main window app, in mainwindow.h:

      @
      ...
      class ContainerBase
      {

      };

      template <class T> class Container: public ContainerBase
      {

      T data;
      };

      Q_DECLARE_METATYPE_TEMPLATE_1ARG(Container)
      @

      what is ConcreteType, a built in one?

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      • N Offline
        N Offline
        NicuPopescu
        wrote on last edited by
        #7

        bq. This gives me a different error “value_type is not an element of Container<T>” in this line of qmetatype.h:
        template<typename T, bool = QMetaTypeId2<typename T::value_type>::Defined>

        this line does not exist here! :) I use qt 5.1.1 mingw

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        • S Offline
          S Offline
          silicomancer
          wrote on last edited by
          #8

          I used an enum class as concrete type and I am using Qt5.2.0 beta here.
          How did you involve QVariant?

          This is a minimum example that breaks compilation when used in one of projects headers:

          @
          template <class T> class Container
          {
          };

          Q_DECLARE_METATYPE_TEMPLATE_1ARG(Container)

          inline void Test()
          {
          QVariant x = QVariant::fromValue(Container<int>());
          }
          @

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          • N Offline
            N Offline
            NicuPopescu
            wrote on last edited by
            #9

            it gives no error here ...

            @Container<int> y = x.value< Container<int> >();@

            returns the correctly too

            shall I understand that Q_DECLARE_METATYPE_TEMPLATE_1ARG is working now?

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            • S Offline
              S Offline
              silicomancer
              wrote on last edited by
              #10

              No, it does NOT work. I also tried the code in one if the Qt examples to make sure there are no collisions in my custom project.

              Adding the following code:

              @
              #include <QVariant>

              template <class T> class Container
              {
              };

              Q_DECLARE_METATYPE_TEMPLATE_1ARG(Container)

              inline void Test()
              {
              QVariant x = QVariant::fromValue(Container<int>());
              }

              @

              to the bottom of the tabdialog.h header of TabWidget example returns errors on building:

              @
              C:\Qt\Qt5.2.0\5.2.0-beta1\msvc2012\include\QtCore\qmetatype.h:1372: Fehler:C2039: 'value_type': Ist kein Element von 'Container<T>'
              with
              [
              T=int
              ]
              C:\Qt\Qt5.2.0\5.2.0-beta1\msvc2012\include\QtCore/qmetatype.h(1578): Siehe Verweis auf die Instanziierung der gerade kompilierten Klassen-template "QtPrivate::SequentialContainerConverterHelper<T>".
              with
              [
              T=Container<int>
              ]

              ..... and a lot more

              @

              If it works for you I suppose this is a Qt 5.2.0 beta problem. I am using 5.2.0 beta, VS2012, ANGLE, 32 Bit.

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              • R Offline
                R Offline
                Rigel
                wrote on last edited by
                #11

                I did this test with Qt5.1.1 (VS2012, ANGLE, 32 Bit) and it worked.

                I also did it with Qt5.2.0-beta1 and it failed.

                So I can definitely confirm that there is some strange issue with Qt5.2.0-beta1 (VS2012, ANGLE, 32 Bit).

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                • SGaistS Offline
                  SGaistS Offline
                  SGaist
                  Lifetime Qt Champion
                  wrote on last edited by
                  #12

                  Hi,

                  It sounds like a regression (I may be wrong though), there has been a lot of work on QMetatype lately. Can you open a bug report so it might get fixed before 5.2 official release ?

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

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                  • N Offline
                    N Offline
                    NicuPopescu
                    wrote on last edited by
                    #13

                    bq. I did this test with Qt5.1.1 (VS2012, ANGLE, 32 Bit) and it worked.
                    I also did it with Qt5.2.0-beta1 and it failed.
                    So I can definitely confirm that there is some strange issue with Qt5.2.0-beta1 (VS2012, ANGLE, 32 Bit).

                    I can confirm these tests too, but I want to do one more with Qt 5.2.0-beta1 with mingw

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                    • N Offline
                      N Offline
                      NicuPopescu
                      wrote on last edited by
                      #14

                      I found a solution for Qt 5.2.0-beta1:

                      @class ContainerBase: public QString /!!!inherits a core class which is compatible with the new meta type system!!!/
                      {

                      };

                      template <class T> class Container: public ContainerBase
                      {
                      T data;

                      };

                      Q_DECLARE_METATYPE_TEMPLATE_1ARG(Container)@

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                      • S Offline
                        S Offline
                        silicomancer
                        wrote on last edited by
                        #15

                        EDIT: I created an issue, see https://bugreports.qt-project.org/browse/QTBUG-34957

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                        • S Offline
                          S Offline
                          silicomancer
                          wrote on last edited by
                          #16

                          Update:

                          According to the report (see above), the Q_DECLARE_METATYPE_TEMPLATE_1ARG in Qt5 seem to work as expected.

                          Unfortunately they do not intend to support registering template types (using a new public macro). So I will need to stick to my nasty workaround :-(

                          Anyway thanks for your help!

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