自定义函数名解决思路

$a = 'test';
eval("function $a(){ echo 'function name is:'.__FUNCTION__;}");
test();

class foo{
    public function __call($name, $param){
        if($name=='test'){
            echo 'test';
        }else{
            echo 'name not exists';
        }
    }
}

$obj = new foo();
$a = 'test';
$obj->$a();