dropping parentheses on template instantiation

[Jarrett Billingsley]

On Sun, Oct 5, 2008 at 2:18 PM, Andrei Alexandrescu
<SeeWebsiteForEmail at erdani.org> wrote:
> I just realized something different. After making an informal review of some
> code, I saw that a large percentage of template instantiations only need ONE
> argument.
>
> This makes me think, with the old "!" notation, parentheses could be dropped
> entirely without prejudice:
>
> auto covariance = Matrix!real(n, n);
> auto normalized = SparseVector!double(n);
>
> and so on.
>
> To the unbridled joy of the enemies of the Sad Pirate, the dot won't work
> for template instantiation because without the parentheses it DOES engender
> ambiguity.
>
> Now say we take the following route:
>
> 1) We find something different from shouting
>
> 2) We drop the parentheses for 1 argument
>
> That sounds like a possible winner. In this case the "#" becomes
> considerably more attractive, in fact very attractive exactly because it
> looks unlike any letter:
>
> auto covariance = Matrix#real(n, n);
> auto normalized = SparseVector#double(n);
>
> Ideas?
>
>
> Andrei
>
> P.S. The Sad Pirate is the emoticon
>
> .(
>
> It doesn't have an eye and is sad, too.
>

Hmm.

I'm trying to think -- is there anywhere in the grammar where something like

Matrix int

would be legal as something else?

That is, I'm suggesting that we take a page from i.e. Haskell's book,
and simply allow the first argument to a template to be separated from
the template name with a space.

auto covariance = Matrix real(n, n);
auto normalized = SparseVector double(n);

Positive real x = 3.4;
Positive real y = 6.8;
Positive real z = y - x; // error

"Identifier Identifier" does not occur anywhere in the grammar either,
as far as I can tell.

Matrix Positive real(n, n);

Please comment!(int);