PHP 链式操作 __call call_user_func

<?php
class Foo {

    private $data;   

public function __construct($data){
$this->data = $data;
}

public function __call($method,$argument=null){

$val = call_user_func($method,$this->data);
$this->data = new Foo($val);
return $this->data;


}

    public function __toString(){ 
        if(is_int($this->data) || is_float($this->data)) 
            $this->data = (string)$this->data; 
        return $this->data; 
    } 
}
$obj = new Foo('  mystr  ');

echo $obj-> trim() ->strlen() -> gettype() ;