Question

I’m just learning PHP, and I’m confused about what the purpose of the __construct() method?

If I can do this:

class Bear {
    // define properties
    public $name = 'Bill';
    public $weight = 200;

    // define methods
    public function eat($units) {
        echo $this->name." is eating ".$units." units of food... <br />";
        $this->weight += $units;
    }
}

Then why do it with a constructor instead? :

class Bear {
    // define properties
    public $name;
    public $weight;

    public function __construct(){

        $this->name = 'Bill';
        $this->weight = 200;
    }
    // define methods
    public function eat($units) {
        echo $this->name." is eating ".$units." units of food... <br />";
        $this->weight += $units;
    }
}

Answer 1

Because constructors can do more complicated logic than what you can do in variable initialization. For example:

class Bear {
  private $weight;
  private $colour;

  public __construct($weight, $colour = 'brown') {
    if ($weight < 100) {
      throw new Exception("Weight $weight less than 100");
    }
    if (!$colour) {
      throw new Exception("Colour not specified");
    }
    $this->weight = $weight;
    $this->colour = $colour;
  }

  ...
}

A constructor is optional but can execute arbitrary code.