interface.php

<?php
// Example 1: ---------------------------------------------------------------------------------
// source: 
// https://www.php.net/manual/en/language.oop5.interfaces.php
// Context:
// Duck typing

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.");
  }
}

// describe these birds please
describe(new Penguin);
echo "---\n";

describe(new Dove);
echo "---\n";

describe(new Duck);

// Example 2: ---------------------------------------------------------------------------------
// source: 
// Context: Webapp

interface WebApp {

    public function login($email, $password);
    public function register($email, $password, $username);
    public function logout();
    
}
// Website 1
class GoogleCom implements WebApp {

    // methods definition
    public function login($email, $password) {
        echo "Login the user with email: " . $email;
    }
    
    public function register($email, $password, $username) {
        echo "User registered: Email=" . $email . " and Username= " . $username;
    }
    
    public function logout() {
        echo "User logged out!";
    }
    
}
/// Another interface
interface CMS {
  public function publishPost($post);
}

// Website 2
class MediumCom implements WebApp, CMS {

    // methods definition
    public function login($email, $password) {
        echo "Login the user with email: " . $email;
    }
    
    public function register($email, $password, $username) {
        echo "User registered: Email=" . $email . " and Username= " . $username;
    }
    
    public function logout() {
        echo "User logged out!";
    }

    public function publishPost($post) {
      echo $post." published!";
  } 
}