import core.stdc.stdio;
interface Timer
{
    final int run() { printf("Timer.run()\n"); fun(); return 1; };
    int fun();
}
interface Application
{
    final int run() { printf("Application.run()\n"); fun(); return 2; };
    int fun();
}

class TimedApp : Timer, Application
{
    int fun()
    {
        printf("TimedApp.fun()\n");
        return 0;
    }
}

void main()
{
    auto app = new TimedApp;
    (cast(Application)app).run();
    (cast(Timer)app).run();
    app.Application.run();
    app.Timer.run();
}

Output:
----
Application.run()
TimedApp.fun()
Timer.run()
TimedApp.fun()
Application.run()
Timer.run()
----

Note how "TimedApp.fun()" is called if cast was used, but not if app.*Interface*. was called. I guess this is a bug?

Yes, this is a bug.

The funny thing here is that instead TimedApp.fun(), object.Object.toString() is called due to shift error in virtual table offset jumping. I guess due to interfaces' ABI a class instance isn't passed properly. Using

    override string toString()
    {
        printf("bzzzz\n");
        return "";
    }

reveals the bug. Valgrind also doesn't detect error like this. Vtable storage layout may explain where bug comes from:

_D4main8TimedApp6__vtblZ:
	dd	offset FLAT:_D4main8TimedApp7__ClassZ@64
	db	000h,000h,000h,000h	;....
	dd	offset FLAT:_D6object6Object8toStringMFZAya@64
	db	000h,000h,000h,000h	;....
	dd	offset FLAT:_D6object6Object6toHashMFNbNeZm@64
	db	000h,000h,000h,000h	;....
	dd	offset FLAT:_D6object6Object5opCmpMFC6ObjectZi@64
	db	000h,000h,000h,000h	;....
	dd	offset FLAT:_D6object6Object8opEqualsMFC6ObjectZb@64
	db	000h,000h,000h,000h	;....
	dd	offset FLAT:_D6object6Object8opEqualsMFC6ObjectC6ObjectZb@64
	db	000h,000h,000h,000h	;....
	dd	offset FLAT:_D4main8TimedApp3funMFZi@64
	db	000h,000h,000h,000h	;....


I remember Don was posting similar issue but do not remember the #.

Actually it was http://d.puremagic.com/issues/show_bug.cgi?id=4589

On Sun, 17 Mar 2013 09:59:03 -0400, Maxim Fomin <maxim@maxim-fomin.ru> wrote:

> Actually it was http://d.puremagic.com/issues/show_bug.cgi?id=4589

I don't think this is the same problem.

I modified the program a bit:

import core.stdc.stdio;
interface Timer
{
    final int run() { printf("Timer.run(), this=%x\n", cast(void*)this); fun(); return 1;}
    int fun();
}
interface Application
{
    final int run() { printf("Application.run(), this=%x\n", cast(void *)this); fun(); return 2; };
    int fun();
}

class TimedApp : Timer, Application
{
    int fun()
    {
        printf("TimedApp.fun(), this=%x\n", cast(void*)this);
        return 0;
    }
}

void main()
{
    auto app = new TimedApp;
    (cast(Application)app).run();
    (cast(Timer)app).run();
    app.Application.run();
    app.Timer.run();
}

New output:

Application.run(), this=10007ff8
TimedApp.fun(), this=10007fe0
Timer.run(), this=10007ff0
TimedApp.fun(), this=10007fe0
Application.run(), this=10007fe0
Timer.run(), this=10007fe0

Note that Application.run() is given the interface pointer 10007ff8, whereas the *true* object pointer is 10007fe0.  This is normal and expected.

However, in the *last* call to Application.run (and Timer.run), it's given the pointer 10007fe0, the true object pointer.  This gives it the completely WRONG vtable to use for calling fun.  I think this is different than the bug I posted.  It may be related, I don't know.

If this bug is not already reported, it should be.

-Steve

Am Tue, 19 Mar 2013 17:51:52 -0400
schrieb "Steven Schveighoffer" <schveiguy@yahoo.com>:

> On Sun, 17 Mar 2013 09:59:03 -0400, Maxim Fomin <maxim@maxim-fomin.ru> wrote:
> 
> > Actually it was http://d.puremagic.com/issues/show_bug.cgi?id=4589
> 
> I don't think this is the same problem.
> 
> I modified the program a bit:
> 
> import core.stdc.stdio;
> interface Timer
> {
>      final int run() { printf("Timer.run(), this=%x\n",
> cast(void*)this); fun(); return 1;}
>      int fun();
> }
> interface Application
> {
>      final int run() { printf("Application.run(), this=%x\n",
> cast(void *)this); fun(); return 2; };
>      int fun();
> }
> 
> class TimedApp : Timer, Application
> {
>      int fun()
>      {
>          printf("TimedApp.fun(), this=%x\n", cast(void*)this);
>          return 0;
>      }
> }
> 
> void main()
> {
>      auto app = new TimedApp;
>      (cast(Application)app).run();
>      (cast(Timer)app).run();
>      app.Application.run();
>      app.Timer.run();
> }
> 
> New output:
> 
> Application.run(), this=10007ff8
> TimedApp.fun(), this=10007fe0
> Timer.run(), this=10007ff0
> TimedApp.fun(), this=10007fe0
> Application.run(), this=10007fe0
> Timer.run(), this=10007fe0
> 
> Note that Application.run() is given the interface pointer 10007ff8, whereas the *true* object pointer is 10007fe0.  This is normal and expected.
> 
> However, in the *last* call to Application.run (and Timer.run), it's given the pointer 10007fe0, the true object pointer.  This gives it the completely WRONG vtable to use for calling fun.  I think this is different than the bug I posted.  It may be related, I don't know.
> 
> If this bug is not already reported, it should be.
> 
> -Steve

I'll report it soon and I already have a bug fix. (The compiler indeed always passed the object pointer. This is valid for base classes, but not for interfaces. Adding an isInterface check + CastExpression solves this issue)