Hi

Starting to use GtkD TreeModel, I write an instance of an abstract class to TreeIter.userData.

When reading back the void pointer and casting to my abstract class leads to crash when instance is used (Task is the abstract class):


        int fillIter(TreeIter iter, Task t)
        {
            if (!t || !iter) return 0;

            iter.stamp = stamp_;

            writeln("writing ", cast(void*)&t);
            iter.userData = cast(void*)&t;

            return 1;
        }


        Task taskFromIter(TreeIter iter)
        {
            if (!iter || iter.stamp != stamp_) return null;

            writeln("reading ", iter.userData);
            writeln(cast(Task)iter.userData);
            return cast(Task)iter.userData;
        }

the code prints
writing 18FC98
reading 18FC98

and crashes at the 2nd writeln call in taskFromIter function with message object.Error@(0): Access violation

The instance is referenced somewhere else in the model, so it should not get garbage collected. should I check this anyway?

Any idea?

thanks
Rémi

On Monday, 18 August 2014 at 10:07:30 UTC, Remi Thebault wrote:
> Hi
>
> Starting to use GtkD TreeModel, I write an instance of an abstract class to TreeIter.userData.
>
> When reading back the void pointer and casting to my abstract class leads to crash when instance is used (Task is the abstract class):
>
>
>         int fillIter(TreeIter iter, Task t)
>         {
>             if (!t || !iter) return 0;
>
>             iter.stamp = stamp_;
>
>             writeln("writing ", cast(void*)&t);
>             iter.userData = cast(void*)&t;
>
>             return 1;
>         }
>
>
>         Task taskFromIter(TreeIter iter)
>         {
>             if (!iter || iter.stamp != stamp_) return null;
>
>             writeln("reading ", iter.userData);
>             writeln(cast(Task)iter.userData);
>             return cast(Task)iter.userData;
>         }
>
> the code prints
> writing 18FC98
> reading 18FC98
>
> and crashes at the 2nd writeln call in taskFromIter function with message object.Error@(0): Access violation
>
> The instance is referenced somewhere else in the model, so it should not get garbage collected. should I check this anyway?
>
> Any idea?
>
> thanks
> Rémi

Classes are reference types. You take reference of local reference (it's address on stack). Use just cast(void*)t

> Classes are reference types. You take reference of local reference (it's address on stack). Use just cast(void*)t

Thank you!