The Iterator is an interface for external iterators or objects that can be iterated themselves internally. In PHP, it is defined as follows.
1 2 3 4 5 6 7 8 9 | Iterator extends Traversable { /* Methods */ abstract public mixed current ( void ) abstract public scalar key ( void ) abstract public void next ( void ) abstract public void rewind ( void ) abstract public boolean valid ( void ) } |
Iterator extends Traversable
{
/* Methods */
abstract public mixed current ( void )
abstract public scalar key ( void )
abstract public void next ( void )
abstract public void rewind ( void )
abstract public boolean valid ( void )
}The following presents a simply clear example that computes the Fibonacci sequence using Iterator. The Fibonacci Number is very well known, probably due to its recursive definition. [read this]
Fibonacci Latex Equation
By implementing the above six methods, the following class can be used as a iterator, e.g. in the foreach statement. The valid tells if the current position is OK, if not, the foreach loop will terminate.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 | class Fib implements Iterator { private $previous = 1; private $current = 0; private $key = 0; public function __construct() { $this->rewind(); } public function key() { return($this->key); } public function current() { return($this->current); } public function next() { $n = $this->current; $this->current += $this->previous; $this->previous = $n; $this->key++; } public function rewind() { $this->previous = 1; $this->current = 0; $this->key = 0; } public function valid() { return(true); } } $seq = new Fib(); $i = 0; foreach ($seq as $f) { echo ($f); if ($i++ === 10) { break; } } |
class Fib implements Iterator
{
private $previous = 1;
private $current = 0;
private $key = 0;
public function __construct()
{
$this->rewind();
}
public function key()
{
return($this->key);
}
public function current()
{
return($this->current);
}
public function next()
{
$n = $this->current;
$this->current += $this->previous;
$this->previous = $n;
$this->key++;
}
public function rewind()
{
$this->previous = 1;
$this->current = 0;
$this->key = 0;
}
public function valid()
{
return(true);
}
}
$seq = new Fib();
$i = 0;
foreach ($seq as $f)
{
echo ($f);
if ($i++ === 10)
{
break;
}
} –EOF (The Ultimate Computing & Technology Blog) —
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