Magento requestShippingRates参数

Question

I am a bit confused about a function:

public function requestShippingRates(Mage_Sales_Model_Quote_Item_Abstract $item)
{
    /** @var $request Mage_Shipping_Model_Rate_Request */
    $request = Mage::getModel('shipping/rate_request');
    $request->setAllItems($item ? array($item) : $this->getAllItems());
}

I know that $item is an arrangement, but what is this Mage_Sales_Model_Quote_Item_Abstract?

Answer 1

For Type Hinting see the reference

As stated in an example on the referenced Page:

<?php
class C {}
class D extends C {}

// This doesn't extend C.
class E {}

function f(C $c) {
    echo get_class($c)."
";
}

f(new C);//C
f(new D);//D
f(new E);//throws exception
?>

The reason Magento is doing this is because you can use one method for both getting the shipping rate for one or all shipping items (when passing invalid data).