Let's code to interface. But why?

interface php http://pastebin.ca/2088573

loosely coupling code http://stackoverflow.com/questions/383947/what-does-it-mean-to-program-to-an-interface

class Horse implements CanEat{

}

class Human implements CanEat{

}

class Table {

}

interface CanEat{
    function eat();
}


$horse = new Horse();

$human = new Human();

// since we know that Horse and Human implemented CanEat interface,
// they obviously have thus methods defined inside CanEat interface. 

function eat(CanEat $canEat){

}

Horse, human and table are concrete classes here.

Basically, interface is a contract. Abstract class.

Using abstract class == easily swappable.