Another PHP5 and C# OOP difference

A few days ago I have found out for myself about one more difference between PHP and C# OOP impelentations. Look at the following code snippet in PHP:

01.class ParentClass {

02.public $val = 'Parent';

03.

04.public function GetValue()

05.{

06.echo $this->val;

07.}

08.}

09.

10.class ChildClass extends ParentClass {

11.public $val = 'Child';

12.}

13.

14.$a = new ChildClass();

15.$a->GetValue();

What do you expect it to show – ‘Parent’ or ‘Child’? The PHP manual says the result will be ‘Child’. And it seems quite logical to me as I would expect public property to be overridden.

Now rewrite the same code to C#:

01.class Parent {

02.public string val = "Parent";

03.

04.public void GetValue() {

05.Console.WriteLine(this.val);

06.}

07.}

08.

09.class Child:Parent {

10.public string val = "Child";

11.}

12.

13.Child child = new Child();

14.child.getValue();

Run the code and you will get ‘Parent’…

Change access modifier of val to private in the parent class. Now both PHP and C# outputs the same – ‘Parent’. Why?

First thing to mention is that unlike PHP, public identifiers cannot be overridden in C#. Calling GetValue(),this points to parent object and returns “not overridden” value of val as a result. Private identifers inside parent are not accessible for the child and therefore are not overridden so everything becomes clear.

To make C# behavior similar to PHP you should either add a method with the same signature and with override keyword to Child class and mark parent method as virtual:

01.class Parent {

02.public string val = "Parent";

03.

04.public virtual void GetValue() {

05.Console.WriteLine(this.val);

06.}

07.}

08.

09.class Child:Parent {

10.public string val = "Child";

11.

12.public override void GetValue() {

13.Console.WriteLine(this.val);

14.}

15.}

or use overridden public properties to access the val value. This will work correctly as unlike public fields, public properties can be overridden.

view source

print?

01.class Parent {

02.private string privateVal = "Parent";

03.public virtual string val

04.{

05.get { return privateVal; }

06.}

07.

08.public void GetValue()

09.{

10.Console.WriteLine(this.val);

11.}

12.}

13.

14.class Child : Parent {

15.private string privateVal = "Child";

16.public override string val

17.{

18.get { return privateVal; }

19.}

20.}

I couln’t find any “standard” behaviour for this case. So I guess it was up to C# and PHP teams how to implement this.

Original post can be found here