typed vtable

[Michel Fortin]

On 2008-11-17 13:56:55 -0500, Harry Vennik <htvennik at zonnet.nl> said:

> Hi,
> 
> One of the things D claims is that it eliminates the need for IDL. And 
> yeah, it does a lot in that direction, but I found something that's 
> missing while trying to actually implement some sense of RPC...
> 
> To get a good view of an interface that can be used to construct the 
> necessary stub code, you need to have a typed vtable. And D almost 
> provides it... You can get the untyped vtable, you can get a typed list 
> of virtual function overloads by name, and you can get the names of all 
> interface members... So you can get all what's needed, except that 
> there is no way to know the vtable index of a member function!!!
> 
> My proposal to fix this is to allow an expression like:
> 
> __traits(getVirtualFunctions, T)           // no second argument!
> 
> where T is an interface or class type (or an expression of such a 
> type). Such an expression should then return all virtual member 
> functions in vtable order, thus making it possible to relate the 
> function itself to its vtable index.

Personally, I had to work around the same problem in the D/Objective-C 
bridge and thus I could probably simplify a few things by having this, 
except that what I need in my case is always the vtable index of a 
particular function. I guess it could be implemented from the above 
__traits syntax, but I'd wish for a simpler solution to my problem, 
such as:

	__traits(getVTableIndex, T.foo);

along with a way to check if a function is virtual, possibly by 
checking they're not final:

	static if (is(T.foo == final)) ...;

This way I could build a pointer template-struct to a virtual member 
function (without knowing the target object in advance as with 
delegates).


-- 
Michel Fortin
michel.fortin at michelf.com
http://michelf.com/