C++0x Concepts - Dead?

[aarti_pl]

Walter Bright pisze:
> aarti_pl wrote:
>> Walter Bright pisze:
>>> aarti_pl wrote:
>>>> My proposal would make meta programing in D much more intuitive 
>>>> (because of using rules - not bunch of corner cases as it is today). 
>>>> Unfortunately almost no one from NG commented on that...
>>>
>>> Thank you, but I don't see in your proposal a method that can:
>>>
>>> 1. instantiate templates only if a value argument is prime or odd.
>>>
>>> 2. instantiate templates only on a type which supports addition and 
>>> has the method foo.
>>>
>>> Note that C++ Concepts could do (2) but could not do (1).
>>
>> ad.1
>>
>> template normalizedType((T U N : U[N=size_t]) && (N & 1))
>>
>> As it is stated in proposal commas are only syntax sugar for more 
>> general form with '&&'.
> 
> How do you distinguish a type from an expression?

Type is in fact the same thing as reduced expression. Please look at 
grammar. Everything except first type is *OPTIONAL*. So in fact you need 
always look for ctexpr (compile time expression) until you find some 
logical or grouping operator.

>> ad.2.
>>
>> This case is in fact the same as 1. Because of the fact that A, B, C 
>> <=> A && B && C, you can create expressions as you want just using 
>> second form with logical operators. In this case you should just use 
>> proper compile time reflection mechanism in D to get information about 
>> type properties.
> 
> class C {
>     int opAdd(C);
> }
> 
> How would I write the parameter to accept any type that supports 
> addition? I want to support int, float, C, etc., without having to 
> exhaustively enumerate them.

I will give you another question instead :-)

How would you do currently in D?

(In fact I just forgot how to do it in D now :-) But give me current 
syntax and I will rewrite it in my syntax)

BR
Marcin Kuszczak