Php Immutable objects

Mutable and immutable classes

A class that contains any methods(not a constructor) that change any of the data in an object of the class is called mutable.

“Mutable” means that something can be changed, and “Immutable” — that something is stable.

That means the mutable objects are those whose data can be changed after the instance is created.

Example of Mutable class

<?php

class Car
{

    /**
     * @var string
     */
    private $color;

    /**
     * @param string $color
     *
     * @return Car
     */
    public function setColor(string $color): Car
    {
        $this->color = $color;
        return $this;
    }

    /**
     * @return string
     */
    public function getColor(): string
    {
        return $this->color;
    }
}

Here we can see the method setColor which changes the state.

$car = new Car();
$car->setColor('red');
$car->setColor('green');
$car->setColor('black');

In this case, we change the state of our PHP object after it’s initialization. Actually we can do this as many times as we want.

Example of Immutable class

<?php

class Car
{
    /**
     * @var string
     */
    private $color;

    /**
     * Car constructor.
     *
     * @param string $color
     */
    public function __construct(string $color)
    {
        $this->color = $color;
    }

    /**
     * @return string
     */
    public function getColor(): string
    {
        return $this->color;
    }
}

$car = new Car('red');

In this case, our PHP object is immutable. We can not change it after initialization.

Where to use immutable classes/objects?

You should use an immutable object when the changing of your application’s status can be critical.

I hope these two simple examples will explain the main difference.

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