Using object property as default for method property

Question

I'm trying to do this (which produces an unexpected T_VARIABLE error):

public function createShipment($startZip, $endZip, $weight = 
$this->getDefaultWeight()){}

I don't want to put a magic number in there for weight since the object I am using has a "defaultWeight" parameter that all new shipments get if you don't specify a weight. I can't put the defaultWeight in the shipment itself, because it changes from shipment group to shipment group. Is there a better way to do it than the following?

public function createShipment($startZip, $endZip, weight = 0){
    if($weight <= 0){
        $weight = $this->getDefaultWeight();
    }
}

Answer 1

This isn't much better:

public function createShipment($startZip, $endZip, $weight=null){
    $weight = !$weight ? $this->getDefaultWeight() : $weight;
}

// or...

public function createShipment($startZip, $endZip, $weight=null){
    if ( !$weight )
        $weight = $this->getDefaultWeight();
}

Answer 2

Neat trick with boolean OR operator:

public function createShipment($startZip, $endZip, $weight = 0){
    $weight or $weight = $this->getDefaultWeight();
    ...
}

Answer 3

This will allow you to pass a weight of 0 and still work properly. Notice the === operator, this checks to see if weight matches "null" in both value and type (as opposed to ==, which is just value, so 0 == null == false).

PHP:

public function createShipment($startZip, $endZip, $weight=null){
    if ($weight === null)
        $weight = $this->getDefaultWeight();
}

Answer 4

You can use a static class member to hold the default:

class Shipment
{
    public static $DefaultWeight = '0';
    public function createShipment($startZip,$endZip,$weight=Shipment::DefaultWeight) {
        // your function
    }
}

Answer 5

Improving upon Kevin's answer if you are using PHP 7 you may do:

public function createShipment($startZip, $endZip, $weight=null){
    $weight = $weight ?: $this->getDefaultWeight();
}