遍历对象

PHP 5 提供了一种定义对象的方法使其可以通过单元列表来遍历,例如用 foreach 语句。默认情况下,所有可见属性都将被用于遍历。

Example #1 简单的对象遍历

<?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();

?>

以上例程会输出:

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

如上所示,foreach 遍历了所有其能够访问的可见属性。

更进一步,可以实现 Iterator 接口。可以让对象自行决定如何遍历以及每次遍历时那些值可用。

Example #2 实现 Iterator 接口的对象遍历

<?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";
}
?>

以上例程会输出:

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:

可以用 IteratorAggregate 接口以替代实现所有的 Iterator 方法。IteratorAggregate 只需要实现一个方法 IteratorAggregate::getIterator(),其应返回一个实现了 Iterator 的类的实例。

Example #3 通过实现 IteratorAggregate 来遍历对象

<?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";
}
?>

以上例程会输出:

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:

Note:

更多遍历的示例见 SPL 扩展

Note:

PHP 5.5 及以后版本的用户也可参考生成器,其提供了另一方法来定义 Iterators。

User Contributed Notes

celsowm 19-Jun-2019 12:51
I've created a dinamic version of grzeniufication code to allow un-, serialize more than one property:

<?php

class Person implements \Serializable {

    public
$id;
    public
$name;
    public
$birthDate;
    public
$surname;

    public function
serialize() {
        return
serialize((array) $this);
    }

    public function
unserialize($serialized): void {

        foreach (
unserialize($serialized) as $p => $v) {
           
$this->{$p} = $v;
        }
    }

}
Anonymous 23-Feb-2018 03:03
szerintetek ez normális, hogy objektumon végigiterálhatsz???
php dot net dot nsp at cvogt dot org 01-Jul-2012 10:25
there is still an open bug about using current() etc. with iterators
https://bugs.php.net/bug.php?id=49369
jille at hexon dot cx 15-May-2012 12:29
Please note that if you implement your iterator this way instead of with an IteratorAggregate you can not nest foreach-loops. This is because when the inner-loop is done the cursor is beyond the last element, then the outer-loop asks for the next element and finds the cursor beyond the last element as the innter-loop left it there.

<?php
 
// Wont work!
foreach($collection as $a) {
  foreach(
$collection as $b) {
   
var_dump($a->someFunc($b));
  }
}
?>
hlegius at gmail dot com 15-Oct-2008 05:06
Iterator interface usign key() next() rewind() is MORE slow than extends ArrayIterator with ArrayIterator::next(), ArrayIterator::rewind(), etc.,
wavetrex A(nospam)T gmail DOT com 01-Mar-2008 02:50
By reading the posts below I wondered if it really is impossible to make an ArrayAccess implementation really behave like a true array ( by being multi level )

Seems like it's not impossible. Not very preety but usable

<?php

class ArrayAccessImpl implements ArrayAccess {

  private
$data = array();

  public function
offsetUnset($index) {}

  public function
offsetSet($index, $value) {
//    echo ("SET: ".$index."<br>");
   
   
if(isset($data[$index])) {
        unset(
$data[$index]);
    }
   
   
$u = &$this->data[$index];
    if(
is_array($value)) {
       
$u = new ArrayAccessImpl();
        foreach(
$value as $idx=>$e)
           
$u[$idx]=$e;
    } else
       
$u=$value;
  }

  public function
offsetGet($index) {
//    echo ("GET: ".$index."<br>");

   
if(!isset($this->data[$index]))
       
$this->data[$index]=new ArrayAccessImpl();
   
    return
$this->data[$index];
  }

  public function
offsetExists($index) {
//    echo ("EXISTS: ".$index."<br>");
   
   
if(isset($this->data[$index])) {
        if(
$this->data[$index] instanceof ArrayAccessImpl) {
            if(
count($this->data[$index]->data)>0)
                return
true;
            else
                return
false;
        } else
            return
true;
    } else
        return
false;
  }

}

echo
"ArrayAccess implementation that behaves like a multi-level array<hr />";

$data = new ArrayAccessImpl();

$data['string']="Just a simple string";
$data['number']=33;
$data['array']['another_string']="Alpha";
$data['array']['some_object']=new stdClass();
$data['array']['another_array']['x']['y']="LOL @ Whoever said it can't be done !";
$data['blank_array']=array();

echo
"'array' Isset? "; print_r(isset($data['array'])); echo "<hr />";
echo
"<pre>"; print_r($data['array']['non_existent']); echo "</pre>If attempting to read an offset that doesn't exist it returns a blank object! Use isset() to check if it exists!<br>";
echo
"'non_existent' Isset? "; print_r(isset($data['array']['non_existent'])); echo "<br />";
echo
"<pre>"; print_r($data['blank_array']); echo "</pre>A blank array unfortunately returns similar results :(<br />";
echo
"'blank_array' Isset? "; print_r(isset($data['blank_array'])); echo "<hr />";
echo
"<pre>"; print_r($data); echo "</pre> (non_existent remains in the structure. If someone can help to solve this I'll appreciate it)<hr />";

echo
"Display some value that exists: ".$data['array']['another_string'];

?>

(in the two links mentioned below by artur at jedlinski... they say you can't use references, so I didn't used them.
My implementation uses recursive objects)

If anyone finds a better (cleaner) sollution, please e-mail me.
Thanks,
Wave.
doctorrock83_at_gmail.com 18-May-2007 03:10
Please remember that actually the only PHP iterating structure that uses Iterator is foreach().

Any each() or list() applied to an Object implementing iterator will not provide the expected result
artur at jedlinski dot pl 22-Apr-2007 12:38
One should be aware that ArrayAccess functionality described by "just_somedood at yahoo dot com" below is currently broken and thus it's pretty unusable.

Read following links to find more:
http://bugs.php.net/bug.php?id=34783
http://bugs.php.net/bug.php?id=32983
rune at zedeler dot dk 27-Feb-2007 08:00
The iterator template from knj at aider dot dk does not yield correct results.
If you do
<?
reset($a);
next($a);
echo current($a);
?>
where $a is defined over the suggested template, then the first element will be output, not the second, as expected.
baldurien at bbnwn dot eu 09-Aug-2006 06:01
Beware of how works iterator in PHP if you come from Java!

In Java, iterator works like this :
<?php
interface Iterator<O> {
 
boolean hasNext();
 
O next();
 
void remove();
}
?>
But in php, the interface is this (I kept the generics and type because it's easier to understand)

<?php
interface Iterator<O> {
 
boolean valid();
 
mixed key();
 
O current();
 
void next();
 
void previous();
 
void rewind();
}
?>

1. valid() is more or less the equivalent of hasNext()
2. next() is not the equivalent of java next(). It returns nothing, while Java next() method return the next object, and move to next object in Collections. PHP's next() method will simply move forward.

Here is a sample with an array, first in java, then in php :

<?php
class ArrayIterator<O> implements Iterator<O> {
  private final
O[] array;
  private
int index = 0;

  public
ArrayIterator(O[] array) {
    
this.array = array;
  }
 
  public
boolean hasNext() {
    return
index < array.length;
  } 

  public
O next() {
     if ( !
hasNext())
       throw new
NoSuchElementException('at end of array');
     return array[
index++];
  }

  public
void remove() {
    throw new
UnsupportedOperationException('remove() not supported in array');
  }
}
?>

And here is the same in php (using the appropriate function) :

<?php
/**
 * Since the array is not mutable, it should use an internal
 * index over the number of elements for the previous/next
 * validation.
 */
class ArrayIterator implements Iterator {
  private
$array;
  public function
__construct($array) {
    if ( !
is_array($array))
      throw new
IllegalArgumentException('argument 0 is not an array');
   
$this->array = array;
   
$this->rewind();
  }
  public function
valid() {
    return
current($this->array) !== false;
   
// that's the bad method (should use arrays_keys, + index)
 
}
  public function
key() {
     return
key($this->array);
  }
  public function
current() {
    return
current($this->array);
  }
  public function
next() {
    if (
$this->valid())
      throw new
NoSuchElementException('at end of array');
   
next($this->array);
  }
  public function
previous()  {
   
// fails if current() = first item of array
   
previous($this->array);
  }
  public function
rewind() {
    
reset($this->array);
  }
}
?>

The difference is notable : don't expect next() to return something like in Java, instead use current(). This also means that you have to prefetch your collection to set the current() object. For instance, if you try to make a Directory iterator (like the one provided by PECL), rewind should invoke next() to set the first element and so on. (and the constructor should call rewind())

Also, another difference :

<?php
class ArrayIterable<O> implements Iterable<O> {
  private final
O[] array;

  public
ArrayIterable(O[] array) {
    
this.array = array;
  } 

  public
Iterator<O> iterator() {
     return new
ArrayIterator(array);
  }
}
?>

When using an Iterable, in Java 1.5, you may do such loops :

<?php
for ( String s : new ArrayIterable<String>(new String[] {"a", "b"})) {
  ...
}
?>
Which is the same as :

<?php
Iterator
<String> it = new ArrayIterable<String>(new String[] {"a", "b"});
while (
it.hasNext()) {
 
String s = it.next();
  ...
}
?>
While in PHP it's not the case :
<?php
foreach ( $iterator as $current ) {
  ...
}
?>
Is the same as :

<?php
for ( $iterator->rewind(); $iterator->valid(); $iterator->next()) {
 
$current = $iterator->current();
  ...
}
?>

(I think we may also use IteratorAggregate to do it like with Iterable).

Take that in mind if you come from Java.

I hope this explanation is not too long...
chad 0x40 herballure 0x2e com 05-May-2006 06:46
The example code given for valid() will break if the array contains a FALSE value. This code prints out a single "bool(true)" and exits the loop when it gets to the FALSE:

<?php
$A
= array(TRUE, FALSE, TRUE, TRUE);
while(
current($A) !== FALSE) {
 
var_dump(current($A));
 
next($A);
}
?>

Instead, the key() function should be used, since it returns NULL only at the end of the array. This code displays all four elements and then exits:

<?php
$A
= array(TRUE, FALSE, TRUE, TRUE);
while(!
is_null(key($A))) {
 
var_dump(current($A));
 
next($A);
}
?>
markushe at web dot de 06-Aug-2005 11:05
Just something i noticed:
It seems, that when you are implementing the interface Iterator, yout method key() has to return a string or integer.

I was trying to return a object an got this error:
Illegal type returned from MyClass::key()
just_somedood at yahoo dot com 27-Jun-2005 12:20
To clarify on php at moechofe's post, you CAN use the SPL to overide the array operator for a class.  This, with the new features of object, and autoloading (among a buch of other things) has me completely sold on PHP5.  You can also find this information on the SPL portion of the manual, but I'll post it here as well so it isn't passed up.  The below Collection class will let you use the class as an array, while also using the foreach iterator:

<?php

class Collection implements ArrayAccess,IteratorAggregate
{
    public
$objectArray = Array();
   
//**these are the required iterator functions   
   
function offsetExists($offset)
    {         
        if(isset(
$this->objectArray[$offset]))  return TRUE;
        else return
FALSE;         
    }   
   
    function &
offsetGet($offset)
    {  
        if (
$this->offsetExists($offset))  return $this->objectArray[$offset];
        else return (
false);
    }
   
    function
offsetSet($offset, $value)
    {         
        if (
$offset$this->objectArray[$offset] = $value;
        else 
$this->objectArray[] = $value;
    }
   
    function
offsetUnset($offset)
    {
        unset (
$this->objectArray[$offset]);
    }
   
    function &
getIterator()
    {
        return new
ArrayIterator($this->objectArray);
    }
   
//**end required iterator functions

   
public function doSomething()
    {
        echo
"I'm doing something";
    }
}

?>

I LOVE the new SPL stuff in PHP!  An example of usage is below:

<?php
class Contact
{
    protected
$name = NULL;

    public function
set_name($name)
    {
       
$this->name = $name;
    }
   
    public function
get_name()
    {
        return (
$this->name);
    }
}

$bob = new Collection();
$bob->doSomething();
$bob[] = new Contact();
$bob[5] = new Contact();
$bob[0]->set_name("Superman");
$bob[5]->set_name("a name of a guy");

foreach (
$bob as $aContact)
{
     echo
$aContact->get_name() . "\r\n";
}
?>

Would work just fine.  This makes code so much simpler and easy to follow, it's great.  This is exactly the direction I had hoped PHP5 was going!
PrzemekG_ at poczta dot onet dot pl 27-May-2005 04:20
If you want to do someting like this:
<?php
foreach($MyObject as $key => &$value)
  
$value = 'new '.$value;
?>
you must return values by reference in your iterator object:
<?php
class MyObject implements Iterator
{
/* ...... other iterator functions ...... */
/* return by reference */
public function &current()
{
   return
$something;
}
?>

This won't change values:
<?php
foreach($MyObject as $key => $value)
  
$value = 'new '.$value;
?>

This will change values:
<?php
foreach($MyObject as $key => &$value)
  
$value = 'new '.$value;
?>

I think this should be written somewhere in the documentations, but I couldn't find it.
elias at need dot spam 10-Apr-2005 03:15
The MyIterator::valid() method above ist bad, because it
breaks on entries with 0 or empty strings, use key() instead:

<?php
public function valid()
{
    return !
is_null(key($this->var));
}
?>

read about current() drawbacks:
http://php.net/current
strrev('ed.relpmeur@ekneos'); 01-Mar-2005 02:25
Use the SPL ArrayAccess interface to call an object as array:

http://www.php.net/~helly/php/ext/spl/interfaceArrayAccess.html
phpnet at nicecupofteaandasitdown dot com 22-Feb-2005 08:09
You should be prepared for your iterator's current method to be called before its next method is ever called. This certainly happens in a foreach loop. If your means of finding the next item is expensive you might want to use something like this

private $item;
       
function next() {
    $this->item = &$this->getNextItem();
    return $this->item;
}
   
public function current() {
     if(!isset($this->item)) $this->next();
    return $this->item;
}
knj at aider dot dk 18-Dec-2004 07:19
if you in a string define classes that implements IteratorAggregate.
you cant use the default;
<?
...
public function getIterator() {
       return new MyIterator(\\$this-><What ever>);
}
..
?>
at least not if you want to use eval(<The string>).
You have to use:
<?
...
public function getIterator() {
      \\$arrayObj=new ArrayObject(\\$this-><What ever>);
      return \\$arrayObj->getIterator();
}
...
?>
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