Object Iteration

PHP 5 provides a way for objects to be defined so it is possible to iterate through a list of items, with, for example a foreach statement. By default, all visible properties will be used for the iteration.

例 10.21. Simple Object Iteration

<?php
class MyClass
{
   public
$var1 = 'value 1';
   public
$var2 = 'value 2';
   public
$var3 = 'value 3';

   protected
$protected = 'protected var';
   private  
$private   = 'private var';

   function
iterateVisible() {
      echo
"MyClass::iterateVisible:\n";
      foreach(
$this as $key => $value) {
          print
"$key => $value\n";
      }
   }
}

$class = new MyClass();

foreach(
$class as $key => $value) {
   print
"$key => $value\n";
}
echo
"\n";


$class->iterateVisible();

?>

上例将输出:

var1 => value 1
var2
=> value 2
var3
=> value 3

MyClass
::iterateVisible:
var1 => value 1
var2
=> value 2
var3
=> value 3
protected => protected var
private => private var
?>

As the output shows, the foreach iterated through all visible variables that can be accessed. To take it a step further you can implement one of PHP 5's internal interface named Iterator. This allows the object to decide what and how the object will be iterated.

例 10.22. Object Iteration implementing Iterator

<?php
class MyIterator implements Iterator
{
   private
$var = array();

   public function
__construct($array)
   {
       if (
is_array($array)) {
           
$this->var = $array;
       }
   }

   public function
rewind() {
       echo
"rewinding\n";
       
reset($this->var);
   }

   public function
current() {
       
$var = current($this->var);
       echo
"current: $var\n";
       return
$var;
   }

   public function
key() {
       
$var = key($this->var);
       echo
"key: $var\n";
       return
$var;
   }

   public function
next() {
       
$var = next($this->var);
       echo
"next: $var\n";
       return
$var;
   }

   public function
valid() {
       
$var = $this->current() !== false;
       echo
"valid: {$var}\n";
       return
$var;
   }
}

$values = array(1,2,3);
$it = new MyIterator($values);

foreach (
$it as $a => $b) {
   print
"$a: $b\n";
}
?>

上例将输出:

rewinding
current
: 1
valid
: 1
current
: 1
key
: 0
0
: 1
next
: 2
current
: 2
valid
: 1
current
: 2
key
: 1
1
: 2
next
: 3
current
: 3
valid
: 1
current
: 3
key
: 2
2
: 3
next
:
current:
valid: ?>

You can also define your class so that it doesn't have to define all the Iterator functions by simply implementing the PHP 5 IteratorAggregate interface.

例 10.23. Object Iteration implementing IteratorAggregate

<?php
class MyCollection implements IteratorAggregate
{
   private
$items = array();
   private
$count = 0;

   
// Required definition of interface IteratorAggregate
   
public function getIterator() {
       return new
MyIterator($this->items);
   }

   public function
add($value) {
       
$this->items[$this->count++] = $value;
   }
}

$coll = new MyCollection();
$coll->add('value 1');
$coll->add('value 2');
$coll->add('value 3');

foreach (
$coll as $key => $val) {
   echo
"key/value: [$key -> $val]\n\n";
}
?>

上例将输出:

rewinding
current
: value 1
valid
: 1
current
: value 1
key
: 0
key
/value: [0 -> value 1]

next: value 2
current
: value 2
valid
: 1
current
: value 2
key
: 1
key
/value: [1 -> value 2]

next: value 3
current
: value 3
valid
: 1
current
: value 3
key
: 2
key
/value: [2 -> value 3]

next:
current:
valid: ?>
注意:

For more examples of iterators, see the SPL Extension.