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<?php /** * An example of duck typing in PHP */ interface CanFly { public function fly(); } interface CanSwim { public function swim(); } class Bird { public function info() { echo "I am a {$this->name}\n"; echo "I am an bird\n"; } } /** * some implementations of birds */ class Dove extends Bird implements CanFly { var $name = "Dove"; public function fly() { echo "I fly\n"; } } class Penguin extends Bird implements CanSwim { var $name = "Penguin"; public function swim() { echo "I swim\n"; } } class Duck extends Bird implements CanFly, CanSwim { var $name = "Duck"; public function fly() { echo "I fly\n"; } public function swim() { echo "I swim\n"; } } /** * a simple function to describe a bird */ function describe($bird) { if ($bird instanceof Bird) { $bird->info(); if ($bird instanceof CanFly) { $bird->fly(); } if ($bird instanceof CanSwim) { $bird->swim(); } } else { die("This is not a bird. I cannot describe it."); } }