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 the 節 called foreach 在 11 章 statement. By default, all public properties will be used for the iteration.

示範 14-14.Simple Object Iteration

<?php

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

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

}

$class = new MyClass();

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

Will output:

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

As the output shows, the the 節 called foreach 在 11 章 iterated through each public variable that is defined. To take it a step further you can implement one of PHP 5's internal the 節 called Object Interfaces named Iterator. This allows the object to decide what and how the object will be iterated.

示範 14-15.Object Iteration implenting 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";
}

Will output:

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.

示範 14-16.Object Iteration implenting 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";
}

?>
</pre>

Will output:

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: