object - interface compatibility

[Pragma]

BCS wrote:
> Actually I would like to see interface calling convention changed to use 
> a fat pointer for interfaces. This would use a arbitrary context pointer 
> welded to a pointer to a v-tbl. All sorts of cool things could be done 
> with this.
> 
> interface literals working like delegate literals
> 3rd party interface implementation for classes*
> interfaces from structs, arrays and any arbitrary pointers.
> 
> In effect any reference can be used as a context and as the basis for an 
> interface

So then the interface method call turns into:

//inf.test(a, b, c);
push c
push b
push a    // push args

mov obj -> r1    // load pointer to object
mov vtbl -> r2    // load v-tbl (obj+vtbl = fat-pointer)
push r1        // push "this"
call r2[test]    // use v-tbl to call test

So, this basically sacrifices stack space in favor of a few less opcodes 
per interface-method call. :)

But doesn't this make cast() operations *longer* by one additional move 
operation?  Are method calls really more numerous than casts?

On the up-side, it would only make the ABI more consistent, since 
delegates are pretty much doing the same thing when compared to their 
function-pointer counterpart (as you already mentioned).  A higher 
degree of consistency there, could buy us a higher degree of consistency 
with D's constructs, cleaner code, and possibly more-bug-free compiler 
implementations.

-- 
- EricAnderton at yahoo