Re: Crash writing and reading back class instance address to void*

[FreeSlave via Digitalmars-d-learn]

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