这一行在课堂上做了什么？ codeigniter相关（parent :: and =＆$ this）[复制]

Question

This question already has an answer here:

• Reference — What does this symbol mean in PHP? 18 answers

Question 1

In CodeIgniter... I've seen some weird stuff... For example:

parent::__Construct(); with no parameters passed into it to load into the construct of the extended class.

I assumed it must be from older PHP versions... I don't really understand what the above would do... I only see value if you pass something into the construct of the extending class.

class Sausage
{
    private $name;
    function __Construct( $something )
    {
        $this->name = $something;
    }
}

class Something extends Sausage
{
    parent::__Construct( "Hi" ); 
    echo $this->name; // outputs "Hi"
}

In Codeigniter, they do not pass anything into the parent::_Construct.. So I do not understand what purpose it serves :S

Question 2

Second of all, WHAT ON EARTH does this mean:

self::$instance =& $this;

In the following snippet from Code Igniter:

class CI_Controller {

 private static $instance;

 public function __construct()
 {
  self::$instance =& $this;

make the $instance variable equal the reference of $this?? $this doesn't account for anything in a static context? i'm confused.

Thanks for your help, totally making me go crazy here.

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Answer 1

For the first question, imagine this setup:

class Animal {
    private $alive;
    public function __construct() {
        $this->alive = true;
    }
    public function isAlive() {
        return $this->alive;
    }
    public function kill() {
        $this->alive = false;
    }
}

class Dog extends Animal {
    private $sound;
    public function __construct() {
        $this->sound = "bark";
    }
}

$dog = new Dog;

What happens if we now call $dog->isAlive()? We get null, because $alive was never set. You need to call parent::__construct() in Dog::__construct, otherwise the bootstrapping in the parent function would never take place.

Obviously in a real world situation the constructors would be much more complex, but this should demonstrate why parent::__construct() would be used.