dropping parentheses on template instantiation

[Sean Kelly]

Andrei Alexandrescu wrote:
> Sean Kelly wrote:
>> Andrei Alexandrescu 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
>>
>> It's a bit off-topic, but why are we required to supply an empty 
>> template list when instantiating a type that has all defaulted 
>> template arguments?  ie.
>>
>>     class C( T = int, U = int ) {}
>>
>>     auto c = new C!();
>>     auto d = new C; // why can't it be this?
>>
>> I asked about this a while back but never got an answer.
> 
> I'd love that. I think there's ambiguity here:
> 
> struct A(T = int)
> {
>     void foo()
>     {
>         auto x = new A;
>     }
> }
> 
> A at double whatever;
> whatever.foo;
> 
> Will x be A at int or A at double?

Darnit, you're right.  And I'm not sure I like the idea of making this 
behavior context-sensitive.

> P.S. Boy I like the "at". Down with the shouting!

You really hate '!', don't you? ;-)


Sean