BCS wrote:
> Reply to Bill,
> 
> 
>>
>> I don't really understand the point of wanting to be able to specify a
>> template argument that could be *anything* -- alias, value, or symbol.
>> Other than a big static if, I can't see how you would be able to
>> implement any functionality when it could be any one of those things.
>>
>> But I'm probably just being dense.
>>
>> --bb
>>
> 
> One thing that it would be useful for would be a tuple template that does something with any tuple type
> 
> // take exactly 2 and return true if they are the same
> template IsSame(A..,B..){const bool IsSame = ...}
> 
> // take 1 or more and remove all of the first from the rest
> template Remove(remove.., from...)
> {
>  static if(from.length == 0)
>  {
>     alias from Remove;
>  }
>  else
>  {
>    staic if(IsSame!(remove, from[0]))
>    {
>       alias Remove!(remove,from[1..$]) Remove
>    }
>    else
>    {
>       alias T!(from[0], Remove!(remove,from[1..$])) Remove
>    }
>  }
> }
> 
> this would work as:
> 
> Remove!(1,4,5,6,7,1,2,3); // gives (4,5,6,7,2,3)
> Remove!(int, byte, short, int, long); // gives (byte, short, long)

Ok.  So it's basically for writing functions that manipulate tuples themselves.  I agree, it does make sense to be able to do that, in a Lisp-y completeness kind of way.

You can write something like Remove!(1).from!(4,5,6,1,2,3,4) now.  Then if the first tuple is empty you just don't remove anything (and you can additionally enhance it to remove any of N things from the list instead of just 1 thing).  But still, tuples are the cons and cdr of template metaprogramming.  There shouldn't be arbitrary restrictions on how you can manipulate them based on what's in the slots.

As an aside, I think Walter's right about the dots.  I misread your example as being two '..'s initially instead of one .. and one ... arg.  I did just wake up though. :-)

--bb

Reply to Bill,


> As an aside, I think Walter's right about the dots.  I misread your
> example as being two '..'s initially instead of one .. and one ...
> arg.
> I did just wake up though. :-)
> --bb
> 

Ahh. The joys of hypothetical syntax!!