Overview

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

What is the State Pattern?

A pattern that allows behavior to be switched by preparing states as classes.

Implementation

An example assuming switching the on/off state of a switch. It might be better to use Singleton.

<?php

class OnState
{
    public function getState()
    {
        return 'ON';
    }

    public function getNextState()
    {
        return new OffState();
    }
}

class OffState
{
    public function getState()
    {
        return 'OFF';
    }

    public function getNextState()
    {
        return new OnState();
    }
}

class Light
{
    public function __construct()
    {
        // Set the default state class
        $this->state = new OffState();
    }

    public function getState()
    {
        return $this->state->getState();
    }

    public function toggle()
    {
        $this->state = $this->state->getNextState();
    }
}


$light = new Light();

echo $light->getState(); // OFF
echo $light->toggle();
echo $light->getState(); // ON
echo $light->toggle();
echo $light->getState(); // OFF

The state class has an image of holding state-specific processing.

It seems to be a pattern that can be considered when there are multiple states and each has complex specific processing.

Impressions

For some reason, this is my favorite pattern among design patterns. It feels like it has an interesting appeal that makes you want to use it.

References

• State Pattern - PHP Design Patterns