Tidy template instantiation syntax

[critic]

bearophile Wrote:

> D has removed some cases of bug-prone C syntax, like:
> 
> int main() {
>     int* ptr1, ptr2;
>     return 0;
> }
> 
> 
> But D needs to avoid introducing new ones. In D2 there is a shortcut to instantiate templates, but it must not cause ambiguity for the eyes of the programmer that reads the code (the point is not about syntax well defined for a compiler, but about syntax that causes no troubles for mammals. The same is true for the bug-prone C syntax).
> 
> So to avoid troubles this code raises a syntax error:
> 
> struct Foo(T) {}
> Foo!Foo!int y;
> void main() {}
> 
> test.d(2): multiple ! arguments are not allowed
> 
> 
> But this code may look ambiguous for human programmers that read unfamiliar code:
> 
> struct Foo(T) {}
> Foo!int* x;
> static assert(!is(typeof(x) == Foo!(int*)));
> static assert(is(typeof(x) == Foo!(int)*));
> void main() {}
> 
> 
> So in such cases I'd like D to require parentheses, so this becomes a syntax error:
> Foo!int* x;
> 
> And you need to write:
> Foo!(int*)
> 
> or:
> Foo!(int)*
> 
> This avoids a possible source of confusion.
> 
> The relative enhancement request:
> http://d.puremagic.com/issues/show_bug.cgi?id=5286
> 
> Bye,
> bearophile

It has been many times said that the template T!X syntax optimization is a very lousy hack with problems. In their arrogance, the authors completely ignore all criticism.