什么时候PHP中的私有方法应该处理类变量，何时应该将这些方法用作函数？

$this->_results

$this->_method($results)

<?php

class TestA
{
    protected $_results;

    public function getResults()
    {
        $this->_results = getFromWebservice();
        $this->_filterResults();
    }

    protected function _filterResults()
    {
        $this->_results = doMagic($this->_results);
    }
}

<?php

class TestB
{
    protected $_results;

    public function getResults()
    {
        $results = getFromWebservice();
        $this->_results = $this->_filterResults($results);
    }

    protected function _filterResults($results)
    {
        return doMagic($results);
    }
}