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Forum Update on Monday, May 27th 2025

Increasing usage for C++ new operators based on data model indexes?

Scheduled Pinned Locked Moved Unsolved General and Desktop
data modelscreateindexallocationnew operatorssoftware design
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  • kshegunovK kshegunov

    @elfring said in Increasing usage for C++ new operators based on data model indexes?:

    Will software libraries evolve further around the suggestion “Add support for usage of placement new together with data model indexes”?

    No they will not.

    E Offline
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    elfring
    wrote on last edited by
    #53

    Why do you think in this direction?

    kshegunovK 1 Reply Last reply
    0
    • E elfring

      Why do you think in this direction?

      kshegunovK Offline
      kshegunovK Offline
      kshegunov
      Moderators
      wrote on last edited by
      #54

      @elfring said in Increasing usage for C++ new operators based on data model indexes?:

      Why do you think in this direction?

      Experience.

      Read and abide by the Qt Code of Conduct

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      • kshegunovK kshegunov

        @elfring said in Increasing usage for C++ new operators based on data model indexes?:

        Why do you think in this direction?

        Experience.

        E Offline
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        elfring
        wrote on last edited by
        #55

        Does your software development experience include the usage of placement new?

        VRoninV kshegunovK 2 Replies Last reply
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        • E elfring

          Does your software development experience include the usage of placement new?

          VRoninV Offline
          VRoninV Offline
          VRonin
          wrote on last edited by
          #56

          Does your software development experience include the usage of QAbstractItemModel?

          I wouldn't question @kshegunov 's abilities as he's firmly in the top tier of developers contributing on this forum.

          "La mort n'est rien, mais vivre vaincu et sans gloire, c'est mourir tous les jours"
          ~Napoleon Bonaparte

          On a crusade to banish setIndexWidget() from the holy land of Qt

          E 1 Reply Last reply
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          • VRoninV VRonin

            Does your software development experience include the usage of QAbstractItemModel?

            I wouldn't question @kshegunov 's abilities as he's firmly in the top tier of developers contributing on this forum.

            E Offline
            E Offline
            elfring
            wrote on last edited by
            #57

            Does your software development experience include the usage of QAbstractItemModel?

            My knowledge is growing also in this software area.

            … he's firmly in the top tier of developers contributing on this forum.

            This is fine.

            Our experiences are varying in several areas, don't they?

            Understanding difficulties can happen then when someone (like me) dares to present special development ideas.

            VRoninV 1 Reply Last reply
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            • E elfring

              Does your software development experience include the usage of QAbstractItemModel?

              My knowledge is growing also in this software area.

              … he's firmly in the top tier of developers contributing on this forum.

              This is fine.

              Our experiences are varying in several areas, don't they?

              Understanding difficulties can happen then when someone (like me) dares to present special development ideas.

              VRoninV Offline
              VRoninV Offline
              VRonin
              wrote on last edited by
              #58

              @elfring said in Increasing usage for C++ new operators based on data model indexes?:

              Understanding difficulties can happen then when someone (like me) dares to present special development ideas.

              Sorry if it came out wrongly before, we are not against new development ideas at all, not on this forum and not in the Qt Project.

              I think what is clear from the discussion above is that nobody here can think of an elegant, efficient, functional and safe way to introduce the concept you suggest in the QAbstractItemModel (or any of its subclasses) interface.
              Having said that, you are correct by saying

              Our experiences are varying in several areas, don't they?

              So our point is, if you have an idea for an implementation then please go ahead and propose it to the community. I'd be very happy to participate in the review process of such an innovation as well as I might end up learning something new (punt not intended)

              "La mort n'est rien, mais vivre vaincu et sans gloire, c'est mourir tous les jours"
              ~Napoleon Bonaparte

              On a crusade to banish setIndexWidget() from the holy land of Qt

              E 1 Reply Last reply
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              • VRoninV VRonin

                @elfring said in Increasing usage for C++ new operators based on data model indexes?:

                Understanding difficulties can happen then when someone (like me) dares to present special development ideas.

                Sorry if it came out wrongly before, we are not against new development ideas at all, not on this forum and not in the Qt Project.

                I think what is clear from the discussion above is that nobody here can think of an elegant, efficient, functional and safe way to introduce the concept you suggest in the QAbstractItemModel (or any of its subclasses) interface.
                Having said that, you are correct by saying

                Our experiences are varying in several areas, don't they?

                So our point is, if you have an idea for an implementation then please go ahead and propose it to the community. I'd be very happy to participate in the review process of such an innovation as well as I might end up learning something new (punt not intended)

                E Offline
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                elfring
                wrote on last edited by
                #59

                …, if you have an idea for an implementation then please go ahead and propose it to the community.

                I guess that progress will depend on this basic clarification:
                Are you familiar with the usage of placement new?

                1 Reply Last reply
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                • VRoninV Offline
                  VRoninV Offline
                  VRonin
                  wrote on last edited by
                  #60

                  The project maintainers are seasoned (15-20 years experience) developers and are familiar with all aspects of standard C++ (especially its oldest parts like placement new).

                  It's safe to assume a total mastery of the placement new concept by people reviewing code, don't worry

                  "La mort n'est rien, mais vivre vaincu et sans gloire, c'est mourir tous les jours"
                  ~Napoleon Bonaparte

                  On a crusade to banish setIndexWidget() from the holy land of Qt

                  E 1 Reply Last reply
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                  • VRoninV VRonin

                    The project maintainers are seasoned (15-20 years experience) developers and are familiar with all aspects of standard C++ (especially its oldest parts like placement new).

                    It's safe to assume a total mastery of the placement new concept by people reviewing code, don't worry

                    E Offline
                    E Offline
                    elfring
                    wrote on last edited by
                    #61

                    It's safe to assume a total mastery of the placement new concept by people reviewing code, don't worry

                    This information is very promising.

                    • Unfortunately, I could not extract corresponding indications of understanding for my proposal so far.
                    • How would you like to clarify a possible mapping from data model indexes to pointers further?
                    VRoninV sierdzioS 2 Replies Last reply
                    0
                    • E elfring

                      It's safe to assume a total mastery of the placement new concept by people reviewing code, don't worry

                      This information is very promising.

                      • Unfortunately, I could not extract corresponding indications of understanding for my proposal so far.
                      • How would you like to clarify a possible mapping from data model indexes to pointers further?
                      VRoninV Offline
                      VRoninV Offline
                      VRonin
                      wrote on last edited by
                      #62

                      @elfring said in Increasing usage for C++ new operators based on data model indexes?:

                      How would you like to clarify a possible mapping from data model indexes to pointers further?

                      That's what we are asking you to propose.
                      We can't think of a way unfortunately

                      "La mort n'est rien, mais vivre vaincu et sans gloire, c'est mourir tous les jours"
                      ~Napoleon Bonaparte

                      On a crusade to banish setIndexWidget() from the holy land of Qt

                      E 1 Reply Last reply
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                      • VRoninV VRonin

                        @elfring said in Increasing usage for C++ new operators based on data model indexes?:

                        How would you like to clarify a possible mapping from data model indexes to pointers further?

                        That's what we are asking you to propose.
                        We can't think of a way unfortunately

                        E Offline
                        E Offline
                        elfring
                        wrote on last edited by
                        #63

                        We can't think of a way unfortunately

                        Why do you stumble on limitations in your imaginations here?

                        J.HilkJ VRoninV 2 Replies Last reply
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                        • E elfring

                          It's safe to assume a total mastery of the placement new concept by people reviewing code, don't worry

                          This information is very promising.

                          • Unfortunately, I could not extract corresponding indications of understanding for my proposal so far.
                          • How would you like to clarify a possible mapping from data model indexes to pointers further?
                          sierdzioS Offline
                          sierdzioS Offline
                          sierdzio
                          Moderators
                          wrote on last edited by
                          #64

                          @elfring said in Increasing usage for C++ new operators based on data model indexes?:

                          Unfortunately, I could not extract corresponding indications of understanding for my proposal so far.

                          Because you have not proposed anything. Show an API and it will be judged. Show a usage example of that API and it will help us know if the API is convenient. Measure with benchmark and we'll know if it improves performance.

                          Without concrete foundations, any idea can be argued endlessly without result.

                          (Z(:^

                          E 1 Reply Last reply
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                          • E elfring

                            We can't think of a way unfortunately

                            Why do you stumble on limitations in your imaginations here?

                            J.HilkJ Offline
                            J.HilkJ Offline
                            J.Hilk
                            Moderators
                            wrote on last edited by
                            #65

                            @elfring said in Increasing usage for C++ new operators based on data model indexes?:

                            We can't think of a way unfortunately

                            Why do you stumble on limitations in your imaginations here?

                            I guess that will depend on this basic clarification:
                            Are you familiar with the usage of placement new?


                            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.

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                            • E elfring

                              We can't think of a way unfortunately

                              Why do you stumble on limitations in your imaginations here?

                              VRoninV Offline
                              VRoninV Offline
                              VRonin
                              wrote on last edited by VRonin
                              #66

                              @elfring said in Increasing usage for C++ new operators based on data model indexes?:

                              Why do you stumble on limitations in your imaginations here?

                              Honestly I just think I'm not smart enough to get into this. It wouldn't be the first time. On the other hand I'd be really happy to see how it could be implemented so I could learn something new

                              "La mort n'est rien, mais vivre vaincu et sans gloire, c'est mourir tous les jours"
                              ~Napoleon Bonaparte

                              On a crusade to banish setIndexWidget() from the holy land of Qt

                              1 Reply Last reply
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                              • sierdzioS sierdzio

                                @elfring said in Increasing usage for C++ new operators based on data model indexes?:

                                Unfortunately, I could not extract corresponding indications of understanding for my proposal so far.

                                Because you have not proposed anything. Show an API and it will be judged. Show a usage example of that API and it will help us know if the API is convenient. Measure with benchmark and we'll know if it improves performance.

                                Without concrete foundations, any idea can be argued endlessly without result.

                                E Offline
                                E Offline
                                elfring
                                wrote on last edited by
                                #67

                                Show an API and it will be judged.

                                Can this application programming interface be just “placement new” (which got the parameters “row” and “column” passed)?

                                VRoninV 1 Reply Last reply
                                0
                                • E elfring

                                  Show an API and it will be judged.

                                  Can this application programming interface be just “placement new” (which got the parameters “row” and “column” passed)?

                                  VRoninV Offline
                                  VRoninV Offline
                                  VRonin
                                  wrote on last edited by VRonin
                                  #68

                                  @elfring said in Increasing usage for C++ new operators based on data model indexes?:

                                  Can this application programming interface be just “placement new” (which got the parameters “row” and “column” passed)?

                                  See, I struggle already, what would the return type be? (void* is a bit useless...)

                                  "La mort n'est rien, mais vivre vaincu et sans gloire, c'est mourir tous les jours"
                                  ~Napoleon Bonaparte

                                  On a crusade to banish setIndexWidget() from the holy land of Qt

                                  E 1 Reply Last reply
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                                  • VRoninV VRonin

                                    @elfring said in Increasing usage for C++ new operators based on data model indexes?:

                                    Can this application programming interface be just “placement new” (which got the parameters “row” and “column” passed)?

                                    See, I struggle already, what would the return type be? (void* is a bit useless...)

                                    E Offline
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                                    elfring
                                    wrote on last edited by
                                    #69

                                    See, I struggle already, what would the return type be?

                                    C++ new operators are returning non-void-pointer types, don't they?

                                    1 Reply Last reply
                                    0
                                    • VRoninV Offline
                                      VRoninV Offline
                                      VRonin
                                      wrote on last edited by
                                      #70

                                      I still can't see a way forward.
                                      The simplest example would probably be QStringListModel. Could you help me understand how the placement new operator would work in that case?

                                      "La mort n'est rien, mais vivre vaincu et sans gloire, c'est mourir tous les jours"
                                      ~Napoleon Bonaparte

                                      On a crusade to banish setIndexWidget() from the holy land of Qt

                                      E 1 Reply Last reply
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                                      • VRoninV VRonin

                                        I still can't see a way forward.
                                        The simplest example would probably be QStringListModel. Could you help me understand how the placement new operator would work in that case?

                                        E Offline
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                                        elfring
                                        wrote on last edited by
                                        #71

                                        Could you help me understand how the placement new operator would work in that case?

                                        Can you understand already that “placement new” provides a pointer to an existing object?

                                        VRoninV 1 Reply Last reply
                                        0
                                        • E elfring

                                          Could you help me understand how the placement new operator would work in that case?

                                          Can you understand already that “placement new” provides a pointer to an existing object?

                                          VRoninV Offline
                                          VRoninV Offline
                                          VRonin
                                          wrote on last edited by
                                          #72

                                          Yes, I can't see a safe way to use that pointer though

                                          "La mort n'est rien, mais vivre vaincu et sans gloire, c'est mourir tous les jours"
                                          ~Napoleon Bonaparte

                                          On a crusade to banish setIndexWidget() from the holy land of Qt

                                          E 1 Reply Last reply
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