Hi,
I've just read your proposal. It is pretty similar to an idea I had over
the weekend. However, there is one thing I want to ask about. But I will
present my idea because it may be the case that I misunderstood some
part from your proposal.
My idea was to introduce few orthogonal concepts and use them together
to solve the DOM problem:
1) single static inheritance and static cast to base types
2) virtual struct WITHOUT any virtual methods
3) dynamic cast to derived type or implemented trait for virtual structs
Structs that are declared virtual will have a hidden pointer to some
vtable-like structure that allows dynamic casting to derived types and
to traits. So the layout is similar to C++'s virtual classes, but there
are no virtual methods. Instead, you would be able to cast to any
implemented trait dynamically. If I understand your proposal correctly,
it is the same as the Fat<T as U> relation.
I see that this Fat<T as U> relation is absolutely doable, but I was not
able to come up with any efficient solution and I see performance of the
dynamic cast as very important property. Otherwise the feature will be
very useful.
My baseline solution was to build hashtable for every crate with key of
pair (T,U) and search the hashtables when the dynamic cast is requested.
That was just a proof that it is doable because it is not efficient
solution. I also expect that some v-table structure can be generated for
each virtual struct as far as we know all the implemented traits. (E.g.,
at link time for entire crate.) But when I considered implementing
traits for virtual struct from different crate, it became more difficult
and I stopped examining the problem.
So my questions would be:
Did I understood the meaning of the Fat<> relation correctly?
Is the Fat<> relation already implemented? Or is there a proposal for
the implementation somewhere?
J
On 03/15/2014 05:30 AM, Micah Chalmer wrote:
I wrote up an alternative proposal that I think, if I’m understanding them
correctly, meets all the requirements. I submitted it as an RFC, so discussion
of it is probably better put on github on the mailing list, but in case anyone
interested is watching this thread and not watching the RFCs:
https://github.com/rust-lang/rfcs/pull/9
-Micah
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