On 5/4/21 6:03 AM, Ola Fosheim Grøstad wrote:
On Tuesday, 4 May 2021 at 01:20:15 UTC, Q. Schroll wrote:
On Saturday, 1 May 2021 at 06:17:36 UTC, Mike Parker wrote:
On Saturday, 1 May 2021 at 04:55:10 UTC, frame wrote:
I always thought as long as an object implements an interface, it
should be able to cast it from a void* if it really points to a
supporting object.
No. An interface is like a pointer to a pointer.
Can you elaborate on this one? I don't really get it. Is an object
handle also like a pointer to a pointer? (I feel like I can learn
something here.)
Off the top of my head the object layout is something like this:
{
pointer to vtable0 for the class;
monitor mutex stuff;
pointer to interface 1 vtable1;
pointer to interface 2 vtable2;
...
pointer to interface N vtableN;
object data 1;
object data 2;
...
}
A pointer to interface 1 is a pointer to the pointer to vtable1 in the
object above.
Yes, this is exactly how it is. See the ABI document:
https://dlang.org/spec/abi.html#classes
So a class reference is *also* a pointer to a pointer (to the vtable),
and a interface reference is the same. However, the slight difference
is, the pointer to the interface doesn't allow useful mechanisms until
you apply the offset (necessitating a double indirection), whereas a
class pointer (combined with compile-time type knowledge) the compiler
can access member fields of the class.
-Steve
