php: php 成员函数创建类的实例

<?php 
    class mc {
        function mcmsg(){
            echo  "mc::mcmsg() !" .PHP_EOL;
        }
        
        function mcget(){
            return new nc();
        }
    }

    class nc {
        function ncget(){
            return new mc();
        }
        function ncmsg(){
            echo  "nc::ncmsg() !" .PHP_EOL;
        }        
    }

$m = new mc();

$m -> mcget() ->ncmsg();

$m -> mcget() -> ncget() -> mcget() -> ncget() -> mcmsg();

?>