phpapprentice/chapters/classes-constructor.md

Whenever you create an object in PHP, you put parentheses after the class name. In the previous examples, we always left the parentheses empty.

<?php

class Hat {
    public $color;

    public function setColor($color)
    {
        $this->color = $color;
    }
}

$hat = new Hat();

However, you can actually pass data into the parentheses like a function. The data will be passed to a special function on the class called a constructor.

class Ballcap
{
    public $color;

    public function __construct($color)
    {
        $this->color = $color;
    }
}

A constructor is not required, but can make creating a new object easier. They are usually used to define the initial value of a property. Instead of writing:

$hat = new Hat();
$hat->setColor('Red');

You can write:

$ballcap = new Ballcap('Blue');

Constructors do not return values because the return value is a always a new object.

class Tophat
{
    public function __construct($color)
    {
        return $color;
    }
}

$tophat now holds an instance of Tophat, not the color "Grey".

$tophat = new Tophat('Grey');