How would you solve this 'interview' question in D?

[MattCoder]

On Wednesday, 26 June 2013 at 22:43:05 UTC, David wrote:
> Am 26.06.2013 22:51, schrieb Gary Willoughby:
> I solved it ;)
>
> http://dpaste.dzfl.pl/5cd56e9d

Yes, but "maybe" the interviewer is waiting just one function, 
since the question was: "Design a function f". So I rewrote your 
example:

import std.stdio;
import std.string;

auto f(T)(T n){
	if(is(T==float))
		return cast(int)n;
	
	return cast(float)-n;
}

void main() {
	foreach(n; int.min..int.max) {
		assert(f(f(n)) == -n);
	}
}

Again, in the same way, maybe the interviewer want "n" as 32 
signed int not a auto/template etc. :D