PHP遍历对象

foreach

PHP5提供了一种可以通过单元列表来遍历对象的方法，如果foreach语句，默认情况下，所有public属性都将被用于遍历。如果在类方法中进行遍历，还可以访问protected和private属性。从父类继承的属性也会被遍历。

<?php
class A{
    public $var1="a";
    public $var2="a2";
    protected $var3="a3";
    private $var4="a4";
    
    public function showProperties(){
        foreach ($this as $key=>$value) {
            echo "$key=$value\n";
        }
    }
}
$a=new A();
$a->showProperties();
foreach ($a as $key=>$value) {
    echo "$key=$value\n";
}
?>

Iterator

如果一个类实现了Iterator接口，则可以自行决定如何遍历以及每次遍历哪些值。当对一个实现了Iterator接口的对象进行foreach遍历的时候，会自动调用Iterator接口中定义的方法，rewind()->valid()->current()->key()->next()->valid()->current()->key()->next().....->valid()直到valid()返回false结束遍历。

遍历之前先调用rewind重置指针，valid验证是否循环结束，current获取当前指针处的值，key获取当前指针处的键，next移动指针，并返回移动后指针处的值。

<?php
class A implements Iterator{
    public $var;
    public $var1;
    protected $var2;
    private $var3;
    private $var4;
    private $arr=array();
    
    public function __construct($arg,$arg1,$arg2,$arg3,$arg4){
        $this->var=$arg;
        $this->var1=$arg1;
        $this->var2=$arg2;
        $this->var3=$arg3;
        $this->var4=$arg4;
        $this->arr["var"]=$arg;
        $this->arr["var1"]=$arg1;
        $this->arr["var2"]=$arg2;
        $this->arr["var3"]=$arg3;
    }
    
    public function rewind() {
        echo "rewinding\n";
        reset($this->arr);
    }

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

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

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

    public function valid() {
        $arr = key($this->arr)!==null;
        echo "valid: {$arr}\n";
        return $arr;
    }
}
$a = new A("a","a1","a2","a3","a4");

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

IteratorAggregate

IteratorAggregate接口可以替代实现Iterator的方法。只需要实现IteratorAggregate接口的getIterator方法即可，此方法应返回一个实现了Iterator接口的类的实例。

<?php
class A implements IteratorAggregate{
    
    public $var;
    private $var1;
    protected $var2;
    private $arr=array();
    
    function __construct($arg,$arg1,$arg2){
        $var=$arg;
        $var1=$arg1;
        $va2r=$arg2;
        $this->arr["var"]=$arg;
        $this->arr["var1"]=$arg1;
        $this->arr["var2"]=$arg2;
    }
    
    function getIterator(){
        return new MyIterator($this->arr);
    }
}

class MyIterator implements Iterator{
    private $vars;
    public function __construct($arr){
        $this->vars=$arr;
    }
    
    public function rewind() {
        echo "rewinding\n";
        reset($this->vars);
    }

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

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

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

    public function valid() {
        $arr = key($this->vars)!==null;
        echo "valid: {$arr}\n";
        return $arr;
    }
}
$a=new A("a","a1","a2");
foreach ($a as $k => $v) {
    print "$k: $v\n";
}
?>