PHP Codeigniter - parent::__construct

Question

When getting inherited from a parent class in PHP, especially in Codeigniter what does parent::__construct or parent::model() do?

How would it make difference if I don't __construct parent class? And, which way is suggested?

-Added-

The focus is more on Codeigniter specific regarding a call to parent::__construct in different ways depending on versions and also if this could be omitted in case Codeigniter would do this automatically.

Answer 1

This is a normal class constructor. Let's look at the following example:

class A {     protected $some_var;      function __construct() {         $this->some_var = 'value added in class A';     }      function echo_some_var() {         echo $this->some_var;     } }  class B extends A {     function __construct() {         $this->some_var = 'value added in class B';     } }  $a = new A; $a->echo_some_var(); // will print out 'value added in class A' $b = new B; $b->echo_some_var(); // will print out 'value added in class B' 

As you see, class B inherits all values and functions from A. So the class member $some_var is accessible from A as well as from B. Because we've added a constructor in class B, the constructor of class A will NOT be used when you are creating a new object of class B.

Now look at the following examples:

class C extends A {     // empty } $c = new C; $c->echo_some_var(); // will print out 'value added in class A' 

As you can see, because we have not declared a constructor, the constructor of class A is used implicitly. But we can also do the following, which is equivalent to class C:

class D extends A {     function __construct() {         parent::__construct();     } } $d = new D; $d->echo_some_var(); // will print out 'value added in class A' 

So you only have to use the line parent::__construct(); when you want a constructor in the child class to do something, AND execute the parent constructor. Example given:

class E extends A {     private $some_other_var;      function __construct() {         // first do something important         $this->some_other_var = 'some other value';          // then execute the parent constructor anyway         parent::__construct();     } } 

More information can be found here: http://php.net/manual/en/language.oop5.php