How to access Variable in parent class using parent:: method

Question

I have Protected Variable UserId in Parent Class.i Am going to extend the variable in my child class as shown below

class Main
{
  protected $UserId          = "151";
  protected static $UserName = "Madhavan";      

  protected function SampleMethod()
  {
    print "This is Sample Method";
  } 
}


class SubMain extends Main
{   
  function __construct()
  {    
    print parent::SampleMethod();

    print "User Id is ".$this->UserId."<br/>";          
    print parent::$UserName;
    print "User Id is ".parent::$UserId."<br/>";            
  }
}

When I Use $this->UserId Its printing fine.But when I use Parent::$UserId its displaying error

Fatal error: Access to undeclared static property: Main::$UserName

Why it is not showing for the function which i Accessed by parent::SampleMethod() as the function is not static.

$UserName is declared as static you need to access it using static:: like static::$UserName — afarazit
– afarazit, Commented Feb 14, 2013 at 9:30

Ja͢ck · Accepted Answer · 2013-02-14 16:38:43Z

3

The scope resolution operator :: sometimes behaves in a non-obvious manner. When applied to constants or variables it always resolves in a static manner.

However, when applied to functions, the execution context of the callee depends on the execution context of the caller code; the context is not changed.

For instance, this works fine without any warnings:

class Test
{
  private $a = 123;

  public function __construct()
  {
    Test::test();
    self::test();
  }

  public function test()
  {
    echo $this->a;
  }
}

new Test();

The call self::test() and Test::test() both run in a non-static manner, because __construct() is called non-statically and you're referencing the same class.

To reference any instance variable, such as $a in the above example, the use of $this-> is required.

edited Feb 14, 2013 at 16:38

answered Feb 14, 2013 at 9:34

Ja͢ck

174k39 gold badges269 silver badges316 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Levente Pánczél · Accepted Answer · 2013-02-14 09:21:25Z

1

This is because functions are overridable (thus older versions of the same name co-exist) while properties are not (declarations simply overwrite each other, and properties should not be re-declared in descendant classes). You always access THE ONLY instance of a property with $this-> if it isn't static, and self:: if it is static. (If a property was declared in multiple ancestor classes, still only one data-field exists, so you cannot reference any "others" or "previous ones".)

answered Feb 14, 2013 at 9:21

Levente Pánczél

1,9332 gold badges14 silver badges16 bronze badges

1 Comment

Levente Pánczél Over a year ago

You can also think of it as follows: all names (functions and properties) that ascendant classes declare are accumulated in a class. You can use any of them just as if they had been declared in this class. There's only one exception: when you want to access previous versions where they are already hidden by a redeclaration of that name. In these cases you can use static calling to name the class that contains the previous version that you want to use. parent is simply a shortcut to name the direct ancestor because this is the most common usecase.

yacon · Accepted Answer · 2013-02-14 09:24:42Z

0

if E_STRICT is not activated you won't get an error, else you will get something like this:

Strict Standards: Non-static method parent::SampleMethod() should not be called statically in...

answered Feb 14, 2013 at 9:24

yacon

1,1121 gold badge10 silver badges17 bronze badges

1 Comment

Ja͢ck Over a year ago

That will not happen, because parent:: doesn't necessarily mean static context.

SoniCoder · Accepted Answer · 2013-02-14 09:30:29Z

0

Instead of using parent, You can access it with self::$UserName attribute (where it was defined) with the self keyword. If You want to reach its value in the child class (because overriding it) it is accessible via final::$UserName (called late static binding)

answered Feb 14, 2013 at 9:30

SoniCoder

4,1643 gold badges38 silver badges44 bronze badges

Collectives™ on Stack Overflow

How to access Variable in parent class using parent:: method

4 Answers 4

Comments

1 Comment

1 Comment

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

Comments

1 Comment

1 Comment

Comments

Your Answer

Sign up or log in

Post as a guest