PHP iterator implements the Fibonacci series Function _ PHP

The Fibonacci series is usually implemented using recursion, and there are other methods. It is now commercially available. it is almost no difficulty to use the PHP iterator to implement a Fibonacci series, just to rewrite the next () method in the class. Annotations have been written into the code, which is quite reasonable. The code is as follows:
Class Fibonacci implements Iterator {
Private $ previous = 1;
Private $ current = 0;
Private $ key = 0;

Public function current (){
Return $ this-> current;
}

Public function key (){
Return $ this-> key;
}

Public function next (){
// The key is here
// Save the current value to $ newprevious
$ Newprevious = $ this-> current;
// Assign the sum of the previous value and current value to the current value
$ This-> current + = $ this-> previous;
// The previous current value is assigned to the previous value.
$ This-> previous = $ newprevious;
$ This-> key ++;
}

Public function rewind (){
$ This-> previous = 1;
$ This-> current = 0;
$ This-> key = 0;
}

Public function valid (){
Return true;
}
}

$ Seq = new maid;
$ I = 0;
Foreach ($ seq as $ f ){
Echo "$ f ";
If ($ I ++ = 15) break;
}

Program running result:
The code is as follows:
0 1 1 2 3 5 8 13 21 34 55 89 144 233 377