Principle of the code to restore php print_r to an array?

<code>class Trie {  
  protected $dict = array();  
  protected $buf = '';  
  function set($word, $value='') {  
    if(is_array($word)) foreach($word as $k=>$v) $this->set($k, $v);  
    $p =& $this->dict;  
    foreach(str_split($word) as $ch) {  
        if(! isset($p[$ch])) $p[$ch] = array();  
        $p =& $p[$ch];  
    }  
    $p['val'] = $value;  
    return $this;  
  }  
  function parse($str) {  
    $this->doc = $str;  
    $this->len = strlen($str);  
    $i = 0;  
    while($i < $this->len) {  
        $t = $this->find($this->dict, $i);  
        if($t) {  
            $i = $t;  
            $this->buf = '';  
        }else $this->buf .= $this->doc{$i++};  
    }  
  }  
  protected function find(&$p, $i) {  
    if($i >= $this->len) return $i;  
    $t = 0;  
    $n = $this->doc{$i};  
    if( isset($p[$n]) ) $t = $this->find($p[$n], $i+1);  
    if($t) return $t;  
    if( isset($p['val']) ) {  
        $ar = explode(',', $p['val']);  
        call_user_func_array( array($this, array_shift($ar)), $ar );  
        return $i;  
    }  
    return $t;  
  }  
  function __call($method, $param) {  
    echo "****\n$this->buf 未定义方法:$method 参数:" . join(',', $param) . "<br />\n";  
  }  
}  
  
  
  
class App extends Trie {  
  public $res = array();  
  protected $stack = array();  
  protected $keyname = '';  
  protected $buf = '';  
  function __construct() {  
    $this->stack[] =& $this->res;  
  }  
  protected function group() {  
    if(! $this->keyname) return;  
    $cnt = count($this->stack) - 1;  
    $this->stack[$cnt][$this->keyname] = array();  
    $this->stack[] =& $this->stack[$cnt][$this->keyname];  
    $this->keyname = '';  
  }  
  protected function brackets($c) {  
    $cnt = count($this->stack) - 1;  
    switch($c) {  
        case ')':  
            if($this->keyname) $this->stack[$cnt][$this->keyname] = trim($this->buf);  
            $this->keyname = '';  
            array_pop($this->stack);  
            break;  
        case '[':  
            if($this->keyname) $this->stack[$cnt][$this->keyname] = trim($this->buf);  
            break;  
        case ']':  
            $this->keyname = $this->buf;  
    }  
    $this->buf = '';  
  }  
}</code>

I have seen this code in several examples. I don’t know the original source. How does it implement print_r to be displayed as an array? Please comment, thank you!
The most commonly used one in the middle is &. I get dizzy after going back and forth a few times.

Reply content:

<code>class Trie {  
  protected $dict = array();  
  protected $buf = '';  
  function set($word, $value='') {  
    if(is_array($word)) foreach($word as $k=>$v) $this->set($k, $v);  
    $p =& $this->dict;  
    foreach(str_split($word) as $ch) {  
        if(! isset($p[$ch])) $p[$ch] = array();  
        $p =& $p[$ch];  
    }  
    $p['val'] = $value;  
    return $this;  
  }  
  function parse($str) {  
    $this->doc = $str;  
    $this->len = strlen($str);  
    $i = 0;  
    while($i < $this->len) {  
        $t = $this->find($this->dict, $i);  
        if($t) {  
            $i = $t;  
            $this->buf = '';  
        }else $this->buf .= $this->doc{$i++};  
    }  
  }  
  protected function find(&$p, $i) {  
    if($i >= $this->len) return $i;  
    $t = 0;  
    $n = $this->doc{$i};  
    if( isset($p[$n]) ) $t = $this->find($p[$n], $i+1);  
    if($t) return $t;  
    if( isset($p['val']) ) {  
        $ar = explode(',', $p['val']);  
        call_user_func_array( array($this, array_shift($ar)), $ar );  
        return $i;  
    }  
    return $t;  
  }  
  function __call($method, $param) {  
    echo "****\n$this->buf 未定义方法:$method 参数:" . join(',', $param) . "<br />\n";  
  }  
}  
  
  
  
class App extends Trie {  
  public $res = array();  
  protected $stack = array();  
  protected $keyname = '';  
  protected $buf = '';  
  function __construct() {  
    $this->stack[] =& $this->res;  
  }  
  protected function group() {  
    if(! $this->keyname) return;  
    $cnt = count($this->stack) - 1;  
    $this->stack[$cnt][$this->keyname] = array();  
    $this->stack[] =& $this->stack[$cnt][$this->keyname];  
    $this->keyname = '';  
  }  
  protected function brackets($c) {  
    $cnt = count($this->stack) - 1;  
    switch($c) {  
        case ')':  
            if($this->keyname) $this->stack[$cnt][$this->keyname] = trim($this->buf);  
            $this->keyname = '';  
            array_pop($this->stack);  
            break;  
        case '[':  
            if($this->keyname) $this->stack[$cnt][$this->keyname] = trim($this->buf);  
            break;  
        case ']':  
            $this->keyname = $this->buf;  
    }  
    $this->buf = '';  
  }  
}</code>

I have seen this code in several examples. I don’t know the original source. How does it implement print_r to be displayed as an array? Please comment, thank you!
The most commonly used one in the middle is &. I get dizzy after going back and forth a few times.

& represents a quote, such as

<code class="php">$a = &$b;</code>

means that $a and $b are the same reference. Modifying $a will also modify the value of $b, and modifying $b will also affect $a. Not adding & means copying the value of $b to $a, both of which are independent.

And adding & to the parameter list of a function (method) means that it is passed by reference. If it is not added, it means that it is passed by value. This is a basic concept of programming. Needless to say.

It should be noted that the object type, whether added or not &, is a reference.

Look at this