Why defining alias and not auto when using a template?

[monarch_dodra]

On Friday, 4 April 2014 at 13:23:48 UTC, Bienlein wrote:
> Hello,
>
> I took some code snippet from some sample D code and modified 
> it a bit:
>
> template TCopy(T, V) {
>   private int i = 2;
> 	
>   void copy(out T to, out V to2, T from) {
>     to = from;
>     to2 = from;
>     writeln("i: ", i);
>   }
> }
>
> void main(string[] args)
> {
> 	int x = 2;
> 	int y = 2;
> 	alias myCopy = TCopy!(int, int);	
> 	myCopy.copy(x, y, 37);
> 	writeln("x: ", x, " y: ", y);
> }
>
> My question is now why I have to declare and alias as in
>
> alias myCopy = TCopy!(int, int);
>
> If I define auto instead of alias, it does not compile. My 
> question is why defining auto does not work. I would consider 
> this more intuitive.
>
> Thanks, Bienlein

"auto" is used to declare an instance, or an object.
"alias" is used to declare a name.

What you are currently doing is saying "the function TCopy!(int, 
int) can now be refered to as myCopy". You aren't actually 
creating any data.