How do I make my class iterable?

[Assembly via Digitalmars-d-learn]

On Monday, 22 June 2015 at 16:52:15 UTC, Ali Çehreli wrote:
> On 06/22/2015 09:37 AM, q66 wrote:
>
>> use opApply.
>
> Yes. Additionally, an InputRange interface can be used:
>
>   http://ddili.org/ders/d.en/foreach_opapply.html
>
> Ali

I was reading exaclty this page that.

I've had implmented this method/properties (I remembered how 
foreach() is translated to for() by the compiler using 
front/popFront() and such):

T front() { return _app.data[index]; }
T front(int index, T a) { return _app.data[index]; }


	void popFront()
	{
		index++;
	}


and called like this:

foreach(int i, MyType p; places) {

but I get this error:

Error: cannot infer argument types, expected 1 argument, not 2

to try solve that error I added the overload method:

T front(int index, T a)

but it didn't worked. How do I solve this?