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

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

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data modelscreateindexallocationnew operatorssoftware design
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  • E elfring
    25 Oct 2018, 18:40

    This is a recipe for disaster

    How many questionable applications do you notice then for the QVector class (for comparison)?

    …, your argument kinda falls apart, doesn't it?

    • This model is for private use by the widget so far, isn't it?
    • Can you eventually get a desire to fiddle with list elements from a data model directly?
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    VRonin
    wrote on 25 Oct 2018, 18:52 last edited by
    #81

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

    How many questionable applications do you notice then for the QVector class (for comparison)?

    QVector is not a QObject subclass. it doesn't have to take care of sending signals to notify other parts of the program that something changed/was added/was removed/was moved.

    This model is for private use by the widget so far, isn't it?

    No. Absolutely not. I often use (and abuse) the model framework even in application that do not have a view.
    It's also used in QML.

    Can you eventually get a desire to fiddle with list elements from a data model directly?

    I don't because I realise how badly it can break the entire framework. The internals of the data model should be handled by the model only, not get exposed otherwise it becomes simply unmanageable

    "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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    • K kshegunov
      25 Oct 2018, 15:42

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

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

      Yes, but then I wonder does yours?

      You are used to the application of ordinary pointers.

      auto x(new my_ball);
      

      How many ball variants would you manage by your QStringListModel example?

      You don't seem to understand that the model is the boundary between the application-level code (i.e. user programmers) and the system-level code (for brevity only, it's the Qt library not the whole system). At that boundary the system code has to provide the means for the application code to map the data, and at the same time the library provides the display of said data.

      At the point when the system is compiled the application-level code does not exist, so the system-level programmer (in this case the Qt Project contributor) can not and will not use anything of type that's unknown to the system. Unknown types include every user type the application provides itself, granted the exception the system has put in place a way for the type to be made known to the system. The latter is done through the meta-type system in Qt, and QVariant is aware of it.

      Is your ball known (i.e. defined) when the models are developed? Of course not. Then the models can't in any conceivable way create that type. The models are generic and use QVariant so they can map multitude of types, not only your own ball.
      Again, provide code that demonstrates your idea, so we can have a reasonable discussion.

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      elfring
      wrote on 25 Oct 2018, 19:01 last edited by
      #82

      Is your ball known (i.e. defined) when the models are developed?

      Models can be implemented in the way that this can happen.

      Again, provide code that demonstrates your idea, …

      How do you think about to discuss concrete consequences for passing a pair of integer types (row, column) to a “placement new”?

      K 1 Reply Last reply 25 Oct 2018, 19:27
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      • E elfring
        25 Oct 2018, 19:01

        Is your ball known (i.e. defined) when the models are developed?

        Models can be implemented in the way that this can happen.

        Again, provide code that demonstrates your idea, …

        How do you think about to discuss concrete consequences for passing a pair of integer types (row, column) to a “placement new”?

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        kshegunov
        Moderators
        wrote on 25 Oct 2018, 19:27 last edited by kshegunov
        #83

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

        Is your ball known (i.e. defined) when the models are developed?

        Models can be implemented in the way that this can happen.

        No they can't.

        How do you think about to discuss concrete consequences for passing a pair of integer types (row, column) to a “placement new”?

        I don't. I already stated directly and quite clearly what is needed to discuss - a proof of concept in code.

        Read and abide by the Qt Code of Conduct

        E 1 Reply Last reply 26 Oct 2018, 07:49
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          VRonin
          wrote on 26 Oct 2018, 07:26 last edited by VRonin
          #84

          I'll try to explain in layman terms why we are a bit frustrated by this and the related topics with a small parallel.
          Imagine you walk into a car factory and say to the manager: "you should put wings on your cars"
          The manager answers: "what would that achieve?"
          you - "do you know what wings are?"
          manager - "yes but I don't see how they can be useful on a car"
          you - "wouldn't it be cool to have wings on the cars?!"
          manager - "yes but wings are not enough to make the cars fly"
          you - "that's right, you need to also make the cars fly"
          manager - "fine but how am I supposed to do that?"
          you - "It's something you should think about"
          manager - "well if you don't have any idea how to make the cars fly, I don't see why i should put wings on my cars"
          you - "wouldn't it be cool to have wings on the cars?!"

          This is exactly what you are doing to us!

          "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 26 Oct 2018, 08:33
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          • K kshegunov
            25 Oct 2018, 19:27

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

            Is your ball known (i.e. defined) when the models are developed?

            Models can be implemented in the way that this can happen.

            No they can't.

            How do you think about to discuss concrete consequences for passing a pair of integer types (row, column) to a “placement new”?

            I don't. I already stated directly and quite clearly what is needed to discuss - a proof of concept in code.

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            elfring
            wrote on 26 Oct 2018, 07:49 last edited by
            #85

            No they can't.

            Why do you try to exclude the possibility that various data can be loaded into models?

            … - a proof of concept in code.

            Do any other aspects hinder you to discuss software design possibilities around returning pointers (or C++ references) from functions after a few parameters were passed?

            K 1 Reply Last reply 26 Oct 2018, 11:21
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            • V VRonin
              26 Oct 2018, 07:26

              I'll try to explain in layman terms why we are a bit frustrated by this and the related topics with a small parallel.
              Imagine you walk into a car factory and say to the manager: "you should put wings on your cars"
              The manager answers: "what would that achieve?"
              you - "do you know what wings are?"
              manager - "yes but I don't see how they can be useful on a car"
              you - "wouldn't it be cool to have wings on the cars?!"
              manager - "yes but wings are not enough to make the cars fly"
              you - "that's right, you need to also make the cars fly"
              manager - "fine but how am I supposed to do that?"
              you - "It's something you should think about"
              manager - "well if you don't have any idea how to make the cars fly, I don't see why i should put wings on my cars"
              you - "wouldn't it be cool to have wings on the cars?!"

              This is exactly what you are doing to us!

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              elfring
              wrote on 26 Oct 2018, 08:33 last edited by
              #86

              Why would you get frustrated by topics (which I presented)?

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              • E elfring
                26 Oct 2018, 07:49

                No they can't.

                Why do you try to exclude the possibility that various data can be loaded into models?

                … - a proof of concept in code.

                Do any other aspects hinder you to discuss software design possibilities around returning pointers (or C++ references) from functions after a few parameters were passed?

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                kshegunov
                Moderators
                wrote on 26 Oct 2018, 11:21 last edited by kshegunov
                #87

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

                Why do you try to exclude the possibility that various data can be loaded into models?

                I don't, and it already can through QVariant.

                Do any other aspects hinder you to discuss software design possibilities around returning pointers (or C++ references) from functions after a few parameters were passed?

                No. I want you to meet the burden or proof - if you claim something, have the balls to back it up. You claim to have an idea that's better than the currently available one, put it on paper, so to speak, and we can discuss it.

                Read and abide by the Qt Code of Conduct

                E 1 Reply Last reply 26 Oct 2018, 12:32
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                • K kshegunov
                  26 Oct 2018, 11:21

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

                  Why do you try to exclude the possibility that various data can be loaded into models?

                  I don't, and it already can through QVariant.

                  Do any other aspects hinder you to discuss software design possibilities around returning pointers (or C++ references) from functions after a few parameters were passed?

                  No. I want you to meet the burden or proof - if you claim something, have the balls to back it up. You claim to have an idea that's better than the currently available one, put it on paper, so to speak, and we can discuss it.

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                  elfring
                  wrote on 26 Oct 2018, 12:32 last edited by
                  #88

                  You claim to have an idea that's better than the currently available one,

                  I got another software development idea which I find useful.

                  put it on paper,

                  I have described it in a few variants for this feature request already.

                  so to speak, and we can discuss it.

                  Another approach

                  • Function input:
                    Parameters like row and column
                  • Function output:
                    • Pointer ⇒ How likely is it that this function variant can be called “C++ new operator”?
                    • C++ reference ⇒ Would you like to use direct access for an object?
                  K 1 Reply Last reply 26 Oct 2018, 16:26
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                  • E elfring
                    26 Oct 2018, 12:32

                    You claim to have an idea that's better than the currently available one,

                    I got another software development idea which I find useful.

                    put it on paper,

                    I have described it in a few variants for this feature request already.

                    so to speak, and we can discuss it.

                    Another approach

                    • Function input:
                      Parameters like row and column
                    • Function output:
                      • Pointer ⇒ How likely is it that this function variant can be called “C++ new operator”?
                      • C++ reference ⇒ Would you like to use direct access for an object?
                    K Offline
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                    kshegunov
                    Moderators
                    wrote on 26 Oct 2018, 16:26 last edited by
                    #89

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

                    I got another software development idea which I find useful.

                    Good. Make a proof of concept for it as well. We can discuss it after that.

                    I have described it in a few variants for this feature request already.

                    You have not written anything tangible for us to discuss. You can describe it all night long, but at the end of the day we have to have something to base the discussion on. Some kind of proposed code that is to replace the current approach and then we can compare and argue.

                    Another approach

                    Finish one of the approaches before jumping into the next one.

                    Read and abide by the Qt Code of Conduct

                    E 1 Reply Last reply 26 Oct 2018, 18:18
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                    • K kshegunov
                      26 Oct 2018, 16:26

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

                      I got another software development idea which I find useful.

                      Good. Make a proof of concept for it as well. We can discuss it after that.

                      I have described it in a few variants for this feature request already.

                      You have not written anything tangible for us to discuss. You can describe it all night long, but at the end of the day we have to have something to base the discussion on. Some kind of proposed code that is to replace the current approach and then we can compare and argue.

                      Another approach

                      Finish one of the approaches before jumping into the next one.

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                      elfring
                      wrote on 26 Oct 2018, 18:18 last edited by
                      #90

                      You have not written anything tangible for us to discuss.

                      Can you discuss the programming interface design for a single function in terms of concepts (without referring to source code examples)?

                      K 1 Reply Last reply 26 Oct 2018, 18:26
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                      • E elfring
                        26 Oct 2018, 18:18

                        You have not written anything tangible for us to discuss.

                        Can you discuss the programming interface design for a single function in terms of concepts (without referring to source code examples)?

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                        kshegunov
                        Moderators
                        wrote on 26 Oct 2018, 18:26 last edited by
                        #91

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

                        Can you discuss the programming interface design for a single function in terms of concepts (without referring to source code examples)?

                        No. There's no interface design for single functions, plus if it's only one function, just write it down for us and we can take a stab at the issue.

                        Read and abide by the Qt Code of Conduct

                        E 1 Reply Last reply 26 Oct 2018, 18:40
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                        • K kshegunov
                          26 Oct 2018, 18:26

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

                          Can you discuss the programming interface design for a single function in terms of concepts (without referring to source code examples)?

                          No. There's no interface design for single functions, plus if it's only one function, just write it down for us and we can take a stab at the issue.

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                          elfring
                          wrote on 26 Oct 2018, 18:40 last edited by
                          #92

                          There's no interface design for single functions,

                          I find this view questionable.

                          plus if it's only one function, just write it down for us and we can take a stab at the issue.

                          template<typename model_item, typename model_index> model_item * get_item_pointer(model_index mx);
                          

                          Can you discuss such a function template declaration better?

                          K 1 Reply Last reply 26 Oct 2018, 18:56
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                          • E elfring
                            26 Oct 2018, 18:40

                            There's no interface design for single functions,

                            I find this view questionable.

                            plus if it's only one function, just write it down for us and we can take a stab at the issue.

                            template<typename model_item, typename model_index> model_item * get_item_pointer(model_index mx);
                            

                            Can you discuss such a function template declaration better?

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                            kshegunov
                            Moderators
                            wrote on 26 Oct 2018, 18:56 last edited by kshegunov
                            #93

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

                            I find this view questionable.

                            That's your right. I will not spend any time arguing it either way.

                            Can you discuss such a function template declaration better?

                            That's a declaration, moreover it's a template, so this declaration doesn't mean anything to me. I have no idea what it is to be doing. Neither can I know how this model_item is to be handled inside the model, nor what model_index is, since it's a generic template type. Additionally there's no clarity of how this function is to be integrated into the QObject derived models, because there are limitations of what moc can parse.

                            Give us some solutions to these problems and I'd be happy to pitch in with ideas, critiques and even work. But only if you take the time to actually prepare something that can reasonably be discussed.

                            Vague notes about theoretical constructs are not acceptable.

                            Read and abide by the Qt Code of Conduct

                            E 1 Reply Last reply 26 Oct 2018, 19:10
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                            • K kshegunov
                              26 Oct 2018, 18:56

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

                              I find this view questionable.

                              That's your right. I will not spend any time arguing it either way.

                              Can you discuss such a function template declaration better?

                              That's a declaration, moreover it's a template, so this declaration doesn't mean anything to me. I have no idea what it is to be doing. Neither can I know how this model_item is to be handled inside the model, nor what model_index is, since it's a generic template type. Additionally there's no clarity of how this function is to be integrated into the QObject derived models, because there are limitations of what moc can parse.

                              Give us some solutions to these problems and I'd be happy to pitch in with ideas, critiques and even work. But only if you take the time to actually prepare something that can reasonably be discussed.

                              Vague notes about theoretical constructs are not acceptable.

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                              elfring
                              wrote on 26 Oct 2018, 19:10 last edited by
                              #94

                              I have no idea what it is to be doing.

                              Your understanding of this programming interface (and my API proposal) might be still incomplete at the moment.
                              But I am confident that you know already what such a function should be doing: You get a pointer for an object based on the provided input data.

                              …, since it's a generic template type.

                              Can you become used to work with templates for software development and involved concepts?

                              K 1 Reply Last reply 26 Oct 2018, 19:12
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                              • E elfring
                                26 Oct 2018, 19:10

                                I have no idea what it is to be doing.

                                Your understanding of this programming interface (and my API proposal) might be still incomplete at the moment.
                                But I am confident that you know already what such a function should be doing: You get a pointer for an object based on the provided input data.

                                …, since it's a generic template type.

                                Can you become used to work with templates for software development and involved concepts?

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                                K Offline
                                kshegunov
                                Moderators
                                wrote on 26 Oct 2018, 19:12 last edited by
                                #95

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

                                Your understanding of this programming interface (and my API proposal) might be still incomplete at the moment.

                                That is for sure, as you have not proposed an API.

                                But I am confident that you know already what such a function should be doing: You get a pointer for an object based on the provided input data.

                                Humor me.

                                Can you become used to work with templates for software development and involved concepts?

                                I already am.

                                Read and abide by the Qt Code of Conduct

                                E 1 Reply Last reply 26 Oct 2018, 19:17
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                                • K kshegunov
                                  26 Oct 2018, 19:12

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

                                  Your understanding of this programming interface (and my API proposal) might be still incomplete at the moment.

                                  That is for sure, as you have not proposed an API.

                                  But I am confident that you know already what such a function should be doing: You get a pointer for an object based on the provided input data.

                                  Humor me.

                                  Can you become used to work with templates for software development and involved concepts?

                                  I already am.

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                                  elfring
                                  wrote on 26 Oct 2018, 19:17 last edited by
                                  #96

                                  …, as you have not proposed an API.

                                  A function template declaration can be a succinct description for an application programming interface, can't it?

                                  K 1 Reply Last reply 26 Oct 2018, 19:18
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                                  • E elfring
                                    26 Oct 2018, 19:17

                                    …, as you have not proposed an API.

                                    A function template declaration can be a succinct description for an application programming interface, can't it?

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                                    kshegunov
                                    Moderators
                                    wrote on 26 Oct 2018, 19:18 last edited by
                                    #97

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

                                    A function template declaration can be a succinct description for an application programming interface, can't it?

                                    No, it can't. Not even by a long shot.

                                    Read and abide by the Qt Code of Conduct

                                    E 1 Reply Last reply 26 Oct 2018, 19:21
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                                    • K kshegunov
                                      26 Oct 2018, 19:18

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

                                      A function template declaration can be a succinct description for an application programming interface, can't it?

                                      No, it can't. Not even by a long shot.

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                                      elfring
                                      wrote on 26 Oct 2018, 19:21 last edited by
                                      #98

                                      No, it can't. Not even by a long shot.

                                      How can your view fit to the C++ standard template library?

                                      K 1 Reply Last reply 26 Oct 2018, 19:23
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                                      • E elfring
                                        26 Oct 2018, 19:21

                                        No, it can't. Not even by a long shot.

                                        How can your view fit to the C++ standard template library?

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                                        kshegunov
                                        Moderators
                                        wrote on 26 Oct 2018, 19:23 last edited by
                                        #99

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

                                        How can your view fit to the C++ standard template library?

                                        It fits perfectly. The STL is comprised by many, many, many functions and classes. They even have bodies too, unlike the one declaration you wrote.

                                        Read and abide by the Qt Code of Conduct

                                        E 1 Reply Last reply 26 Oct 2018, 19:36
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                                        • K kshegunov
                                          26 Oct 2018, 19:23

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

                                          How can your view fit to the C++ standard template library?

                                          It fits perfectly. The STL is comprised by many, many, many functions and classes. They even have bodies too, unlike the one declaration you wrote.

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                                          elfring
                                          wrote on 26 Oct 2018, 19:36 last edited by
                                          #100

                                          The STL is comprised by many, many, many functions and classes.

                                          My proposal can eventually grow into another template library, can't it?

                                          They even have bodies too, unlike the one declaration you wrote.

                                          The desired implementation can evolve further if the required concepts will be generally accepted.

                                          K 1 Reply Last reply 26 Oct 2018, 19:42
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