Bug 1712 – vtbl[0] for interface not set to corresponding Interface*

From the spec: """ struct Interface; Information about an interface. A pointer to this appears as the first entry in the interface's vtbl[]. """ By implication, the vtbl has to be a void* array of length one, and the first entry must be non-null. --- interface IFoo {}; writefln("%x", IFoo.classinfo.vtbl.ptr); // prints '0' ---

The vtbl[] for an interface is not in the interface's classinfo, as the vtbl[] is not generated by the interface definition, but by the class definition that implements the interface.

So you're saying that the Interface* should appear in the vtbl of each implementing class? Like this: --- interface IFoo {} class Foo : IFoo {} // Foo implements one more interface than Object, so its vtbl includes // one Interface* that Object doesn't. Nothing else is specific to Foo. assert(Object.classinfo.vtbl.length + 1 == Foo.classinfo.vtbl.length); --- Except that doesn't work. I understand that the vtbl of an interface should not include any function pointers. However, the spec says it should hold an Interface*. http://www.digitalmars.com/d/phobos/object.html if you want the link. Either the spec is incorrect or the implementation is incorrect. If the spec is incorrect, then I cannot proxy certain objects, and you should alter the documentation. Or is there some other vtbl in which the Interface* should appear? If so, the documentation is far from clear on the matter and should be altered.

Please amend the documentation to say: "When an object is accessed via an interface, an Interface* appears as the first entry in its vtbl." Thanks to Bill Baxter for digging up a link related to this issue.

Fixed dmd 1.029 and 2.013