C++0x Concepts - Dead?

[BLS]

Walter Bright wrote:
> Christian Kamm wrote:
>>> Christian Kamm wrote:
>>>> Is there a difference between
>>>> template Foo(T : U) {} and
>>>> template Foo(T) if(is(T : U)) {} ?
>>>>
>>
>> Walter Bright wrote:
>>> Yes. Constraints determine the list of candidate template declarations,
>>> but do not participate in the partial ordering of candidates to
>>> determine the 'best' match.
>>
>> Thanks for the explanation!
>>
>> I expect the reason is that for constrained templates it is impossible 
>> to determine whether all valid template arguments for one would lead 
>> to a valid instantiation of another?
>>
>>
> 
> That's a good technical reason, but I also felt that the current way 
> just made intuitive sense.

The current Template specialization implementation is doing a best fit 
search anyway, so why constraints are not able to use the same mechanism. ?

So, instead of IFTI we should have EFTI*, driven by constraints.
*The name is rather confusing so "fuzzy templates" are probably better.

bearophile brings in several times Scala/OCAML like pattern matching. 
Why not using that for constraints ?

IMO the current D constraints implementation is nice and easy, but I 
thing there is much more hidden power in that idea.

Thanks for ignoring my ignorance..