PHP设计模式之迭代器模式的深入解析

    <?php
    /** 
     * Collection that wraps a numeric array. 
     * All five public methods are needed to implement 
     * the Iterator interface. 
     */ 
    class Collection implements Iterator 
    { 
 private $_content; 
 private $_index = 0; 

 public function __construct(array $content) 
 { 
     $this->_content = $content; 
 } 

 public function rewind() 
 { 
     $this->_index = 0; 
 } 

 public function valid() 
 { 
     return isset($this->_content[$this->_index]); 
 } 

 public function current() 
 { 
     return $this->_content[$this->_index]; 
 } 

 public function key() 
 { 
     return $this->_index; 
 } 

 public function next() 
 { 
     $this->_index++; 
 } 
    } 

    $array = array('A', 'B', 'C', 'D'); 
    echo "Collection: "; 
    foreach (new Collection($array) as $key => $value) { 
 echo "$key => $value. "; 
    } 
    echo "n";
    /** 
     * Usually IteratorAggregate is the interface to implement. 
     * It has only one method, which must return an Iterator 
     * already defined as another class (e.g. ArrayIterator) 
     * Iterator gives a finer control over the algorithm, 
     * because all the hook points of Iterator' contract 
     * are available for implementation. 
     */ 
    class NumbersSet implements IteratorAggregate 
    { 
 private $_content; 

 public function __construct(array $content) 
 { 
     $this->_content = $content; 
 } 

 public function contains($number) 
 { 
     return in_array($number, $this->_content); 
 } 

 /** 
  * Only this method is necessary to implement IteratorAggregate. 
  * @return Iterator 
  */ 
 public function getIterator() 
 { 
     return new ArrayIterator($this->_content); 
 } 
    } 

    echo "NumbersSet: "; 
    foreach (new NumbersSet($array) as $key => $value) { 
 echo "$key => $value. "; 
    } 
    echo "n";
    // let's play with RecursiveIterator implementations 
    $it = new RecursiveArrayIterator(array( 
 'A', 
 'B', 
 array( 
     'C', 
     'D' 
 ), 
 array( 
     array( 
  'E', 
  'F' 
     ), 
     array( 
  'G', 
  'H', 
  'I' 
     ) 
 ) 
    )); 
    // $it is a RecursiveIterator but also an Iterator, 
    // so it loops normally over the four elements 
    // of the array. 
    echo "Foreach over a RecursiveIterator: "; 
    foreach ($it as $value) { 
 echo $value; 
 // but RecursiveIterators specify additional 
 // methods to explore children nodes 
 $children = $it->hasChildren() ? '{Yes}' : '{No}'; 
 echo $children, ' '; 
    } 
    echo "n"; 
    // we can bridge it to a different contract via 
    // a RecursiveIteratorIterator, whose cryptic name 
    // should be read as 'an Iterator that spans over 
    // a RecursiveIterator'. 
    echo "Foreach over a RecursiveIteratorIterator: "; 
    foreach (new RecursiveIteratorIterator($it) as $value) { 
 echo $value; 
    } 
    echo "n";