Parameter-less templates?

[Tommi]

On Tuesday, 13 August 2013 at 09:41:45 UTC, monarch_dodra wrote:
>
> In regards to template (I mean the actual "template"), I guess 
> I wish we could either:
> 1. Allow non-parameterized templates (eg template foo {...})
> 2. Allow invoking a template without parameters (provided the 
> template has 0 parameters, or default parameters), without 
> doing "!()"

I think your proposal no. 1 is good, but there's a problem with 
your proposal no. 2. This is current D code:

template get(int n = 1)
{
     static if (n == 1) {
         alias get = one;
     }
     else static if (n == 0) {
         enum get = 0;
     }
}

template one(int n)
{
     enum one = 1;
}

template wrap(alias a)
{
     enum wrap = a!0;
}

void main()
{
     static assert(wrap!get == 0);
     static assert(wrap!(get!()) == 1);
}

So, if we go with your proposal no. 2 (allow invoking a template 
without a parameter list), then the meaning of 'get' in:
wrap!get
...becomes ambiguous. We could be either passing an alias to 
'get', or an alias to a parameterless instantiation of template 
'get', i.e. get!().