struct foo(T, T a) {}

void bar(T, T a)(foo!(T, a) f) {}

void main()
{
	foo!(float, 0) f;
	bar!(float, 0)(f); // cannot implicitly convert expression (f) of type foo!(float,0) to foo!(float,A)
}

If a's type is instead set in the template definition, this compiles correctly.