Is this a bug?

[Márcio Martins]

On Monday, 15 October 2018 at 16:46:34 UTC, Steven Schveighoffer 
wrote:
> On 10/15/18 12:40 PM, Márcio Martins wrote:
>> import std.stdio;
>> 
>> void incx(T, Args...)(ref T t) {
>>      ++t.x;
>> }
>> 
>> static struct Test(T) {
>>      T x;
>> }
>> 
>> void main() {
>>      Test!uint t;
>>      t.incx();           // works
>>      t.incx!();          // works
>>      incx(t);            // works
>>      t.incx!(1, 2, 3);   // what?
>>      incx(t, 1, 2, 3);   // what?
>>      writeln(t.x);
>> }
>> 
>> 
>> test.d(16): Error: template test.incx cannot deduce function 
>> from argument types !(1, 2, 3)(Test!uint), candidates are:
>> test.d(3):        test.incx(T, Args...)(ref T t)
>
> No, not a bug.
>
> I suspect you want this?
>
> void incx(Args..., T)(ref T t);

This doesn't seem to work, because:
test.d(3): Error: template `test.incx(Args..., T)(ref T t)` 
template tuple parameter must be last one

Are you sure it's not a bug? It would be very un-intuitive 
otherwise, no?
Considering that the declaration is legal, and that the template 
parameter deduction works when Args.length == 0, but stops 
working when Args.length > 0.

There seems to be no way around it, except manually specifying 
the type, which is not only annoying.

I was trying to use UFCS to emulate a method on a family of 
structs, but this makes it impossible :(