PHP Interfaces Can Extend Multiple Interfaces

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Every PHP programmer knows you can’t extend multiple classes with PHP. You can only do one - which is fine. In fact, if you need more shared code, make sure to focus on using traits instead.

What I didn’t realize, until recently, is that PHP Interfaces can extend multiple other interfaces, though. (I admit, I haven’t been much of a contract-based programmer until recently.) Let me show you what I mean:

interface Talks
{
  public function say(string $message);
}

interface Eats
{
  public function putInMouth(FoodObject $food);
}

interface Human extends Talks, Eats
{
  public function singsOffKey(SongObject $song);
}

Now, when you have an object that implements the Human interface, it’s going to have to define the putInMouth and say methods in addition to the singsOffKey method. Pretty sweet.

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