About template template arguments syntax

[Timon Gehr]

On 10/02/2011 02:44 PM, Philippe Sigaud wrote:
> On Sun, Oct 2, 2011 at 04:20, bearophile<bearophileHUGS at lycos.com>  wrote:
>> This little program is a reduction of code recently shown around here:
>>
>>
>> template Spam(T, alias P) { enum Spam = P!T; }
>> template Foo(T, Preds...) {
>>     enum bool Foo = Spam!(T, Preds[0]);
>> }
>> template Bar(T) { enum Bar = true; }
>> static assert(Foo!(int, Bar));
>> void main() {}
>>
>>
>> Do you know why the P argument of Spam needs "alias" before?
>
> Because P is a template name, not a type. 'Bar' is not a type, it's a
> template: a blueprint for producing code. Symbols, can only be
> manipulated in D through aliases (though it's cool they can be
> manipulated at all!)
>
>
>> The type tuple Preds of Foo doesn't need an "alias" before.
>
> Because template parameters tuples are mongrel constructs, able to
> store both types and aliases. Tuples members are automatically
> aliases, if you will.
>
>
>> Isn't it possible to remove the need to use such "alias" for template template arguments in D? (This is a question I've had to ask since a lot of time).
>
> That sure would simplify some code, particularly when you write
> generic code that deals with both types and symbols (Yes, it happens).
> I don't know if it's possible and/or if it's a good idea or not.
>

Types are symbols, so just using alias template arguments works.