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Q:

constructor - Why is PHP private variables working on extended class?

Hi everyone,

I hope you are all doing well. I have been working on PHP recently and I came across a situation that I find a bit confusing. I was experimenting with inheritance and encountered a scenario where private variables in the parent class were accessible in the child class. This goes against what I initially understood about private variables and I'm trying to wrap my head around it.

Here's an example to illustrate my point:

```
class ParentClass {
private $privateVariable = "I am private";

public function getPrivateVariable() {
return $this->privateVariable;
}
}

class ChildClass extends ParentClass {
public function printPrivateVariable() {
echo $this->privateVariable;
}
}

$childObj = new ChildClass();
$childObj->printPrivateVariable(); // Output: "I am private"
```

In the above example, I was expecting that `$this->privateVariable` would be inaccessible in the child class since it is declared as private in the parent class. However, the code runs without any errors and successfully prints the value of the private variable.

I would really appreciate it if someone could help me understand why this is happening. It seems to contradict the principle of encapsulation that private variables should not be directly accessible outside the class they are defined in.

Thank you in advance for your assistance!

Best regards,
[Your Name]

All Replies

ernest25

Hello everyone,

I've encountered a similar situation in PHP inheritance, and I can understand why it might seem counterintuitive. Private variables are indeed meant to be inaccessible outside the class where they are defined, even by the extending child classes.

However, in PHP, despite the visibility being declared as private, child classes can still access these private variables of their parent classes. It might appear to violate the principle of encapsulation, but there's a reasoning behind this behavior.

PHP's approach is based on a concept called "limited encapsulation." While private variables should technically be hidden from external contexts, they are accessible within the class hierarchy. This allows child classes to leverage and build upon the functionality of the parent class, even if it means accessing private variables.

Now, why is this the case? The main reason is practicality. By granting access to private variables within the class hierarchy, PHP promotes code reusability and a smoother inheritance model. Child classes have the ability to access and manipulate these private variables directly, without having to rely solely on public or protected methods.

However, it's crucial to note that altering or directly accessing parent class's private variables in the child class can be risky. It breaks encapsulation and can lead to potential issues. It's generally considered a best practice to access and modify parent class variables through public or protected methods. This helps maintain encapsulation and ensures proper data manipulation.

In summary, PHP's behavior allows child classes to access private variables of their parent classes, but it's essential to exercise caution and follow best practices for code maintainability and encapsulation.

If you have any other questions or need further clarification, feel free to ask!

Best regards,
[Your Name]

kub.haven

Hey there,

I've come across this confusion before, and it's definitely a tricky concept in PHP inheritance. In PHP, the private visibility modifier doesn't restrict access to the variable within the class it is defined in, but rather it restricts access from any external contexts, like other classes or instances.

However, when it comes to inheritance, a child class can gain access to private variables of its parent class. PHP allows this behavior to facilitate the child class's ability to inherit and extend the functionality of the parent class.

In your example, the child class `ChildClass` extends `ParentClass`, which means that it inherits all the properties and methods of the parent. Since the private variable `$privateVariable` is a part of the parent class, it can be accessed by the child class.

The reason for this is that the child class is considered a part of the parent class, in a sense. It has the privilege of accessing the private variables directly, while external classes or instances would not.

To maintain encapsulation and restrict access to variables, you should use the protected visibility modifier instead of private. Protected variables can be accessed within the class itself as well as any child classes, but they remain inaccessible outside the class hierarchy.

I hope this helps clarify the behavior of private variables in inheritance. If you have any further questions, feel free to ask.

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