对象迭代

2022-10-18 22:19:33
内容摘要
对象迭代,PHP5提供了一种迭代（iteration）对象的功能，就像使用数组那样，可以通过foreach 来遍历对象中的属性。默认情况下，在外部迭代只能得到外部可见的属性的值。
文章正文

对象迭代

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. PHP5提供了一种迭代（iteration）对象的功能，就像使用数组那样，可以通过foreach 来遍历对象中的属性。默认情况下，在外部迭代只能得到外部可见的属性的值。

Example #1 简单的对象迭代

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<code><?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: ";
       foreach($this as $key => $value) {
           print "$key => $value ";
       }
    }
}
 
$class = new MyClass();
 
foreach($class as $key => $value) {
    print "$key => $value ";
}
echo " ";
 
 
$class->iterateVisible();
 
?></code>

以上例程会输出：

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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,the foreach 遍历了所有 可见的 属性. 你也可以通过实现PHP 5自带的 Iterator接口来实现迭代. 使用Iterator接口可以让对象自行决定如何迭代自已。
 

Example #2 实现Iterator接口的迭代

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<code><?php
class MyIterator implements Iterator
{
    private $var = array();
 
    public function __construct($array)
    {
        if (is_array($array)) {
            $this->var = $array;
        }
    }
 
    public function rewind() {
        echo "rewinding ";
        reset($this->var);
    }
 
    public function current() {
        $var = current($this->var);
        echo "current: $var ";
        return $var;
    }
 
    public function key() {
        $var = key($this->var);
        echo "key: $var ";
        return $var;
    }
 
    public function next() {
        $var = next($this->var);
        echo "next: $var ";
        return $var;
    }
 
    public function valid() {
        $var = $this->current() !== false;
        echo "valid: {$var} ";
        return $var;
    }
}
 
$values = array(1,2,3);
$it = new MyIterator($values);
 
foreach ($it as $a => $b) {
    print "$a: $b ";
}
?></code>

以上例程会输出：

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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:

你也可以让类实现IteratorAggregate接口，这样你的类就不用强制性地实现 Iterator接口中的所有方法。

Example #3 通过IteratorAggregate来实现对象迭代

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<code><?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] ";
}
?></code>

以上例程会输出：

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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:
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作者：喵哥笔记

IDC笔记

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