Get function argument name?

[JN]

On Sunday, 4 March 2018 at 21:12:44 UTC, arturg wrote:
>
> you can pass it by alias:
>
> import std.stdio;
>
> void main(string[] args)
> {
>     int x;
>     printName!(x);
> }
>
> void printName(alias var)()
> {
>     writeln(__traits(identifier, var), " ", var);
> }

Well, it works. But I am confused now, why. Isn't alias only for 
types (like a typedef)? Why can we use it for variable here?