Array.Sort(Array arr)

[blackjack2150]

It just came to my mind... The method sorts the provided array, but it doesn't require ref or out parameter (C#). How does it alter the elements of the array then? Does it use explicit pointers internally? Just wondering... Thanks.

[vekipeki]

You don't have to access internal array properties to sort it, because it's sorted "in place" (i.e. no resizing or memory allocation is being done), the original internal array is still the same object.

It also does not alter the elements of the array, it just makes the array point to those elements in a different order.

[blackjack2150]

I still don't get it, sorry...
The Array.Sort() method changes the provided array object, does it not? But the parameter is passed by value, not by reference. Then, how come a parameter that is passed by value be altered after the method call returns?

[vekipeki]

When you are passing a class (any class, including Array) to a method without the "ref" keyword, you are still actually passing a reference to the actual object.

Consider the following code:

class Program
{
    public class Data
    {
        public int a;
    }
 
    public static void Change(Data data)
    {
        data.a = 20;
    }
 
    static void Main(string[] args)
    {
        Data data = new Data();
        data.a = 10;
 
        Change(data);
        Console.WriteLine(data.a); // a is now 20
    }
}
 

You can see that "data" variable is pointing to the same object during its lifetime. The "Change()" method accesses that object and really changes the "a" property, although it is not passed with a "ref" keyword.

If we had passed "data" using a "ref" keyword, we would be actually passing a reference to our "data" variable, not to the actual object. In that case, we could make "data" point somewhere else inside the "Change()" method, and it would reflect in the main program also.

So, when passing a reference value (any class instance) to a method, remember:

• Without "ref" keyword - you are passing a reference to your object
• With "ref" keyword - you are passing a reference to the actual variable which points to your object

[blackjack2150]

I understand now. Great answer! Thanks for taking the time to explain.