Overview

An article that didn't make it in time for the PHP Design Patterns Advent Calendar 2018.

What is the Mediator Pattern?

It means mediator or arbitrator.

A behavioral design pattern that coordinates interactions between objects.

It might be useful when interactions between objects become complex and relationships become difficult to see.

Implementation

<?php

// Mediator
class Receptionist
{
    public function checkIn(User $user, $message) // Holds the object to which you want to delegate behavior operations
    {
        echo $message . ' ' . $user->getName();
    }
}

class User
{
    private $name;
    private $receptionist;

    public function __construct($name, Receptionist $receptionist) // Holds the Mediator
    {
        $this->name = $name;
        $this->receptionist = $receptionist;
    }

    public function getName()
    {
        return $this->name;
    }

    public function checkIn($message)
    {
        $this->receptionist->checkIn($this, $message); // $this!!
    }
}

$receptionist = new Receptionist();


$john = new User('John', $receptionist);
$bob = new User('Bob', $receptionist);

$john->checkIn('Welcome!'); // Welcome! John
$bob->checkIn('Hi!'); // Hi! Bob