求教php基础有关问题

<br />
a()->b()->c();<br />
function a() {<br />
$r = new obj1;<br />
return $r;<br />
}<br />
class obj1{<br />
public function b(){<br />
$r=new obj2;return $r<br />
}<br />
}<br />
class obj2{<br />
public function c(){<br />
//do something<br />
}<br />
}<br />

class T {<br />
  function b($v) {<br />
    echo $v;<br />
    return $this;<br />
  }<br />
  function c($v) {<br />
    echo $v;<br />
    return $this;<br />
  }<br />
}<br />
function a($v) {<br />
  echo $v;<br />
  return new T;<br />
}<br />
<br />
a('aa')->b('bb')->c('cc');<br />