Question

Possible Duplicates:
Why use ref keyword when passing an Object?
When to pass ref keyword in

What is the correct usage of the ‘ref’ keyword in C#. I believe there has been plenty of discussion threads on this, but what is not clear to me is:

1. Is the ref keyword required if you are passing in a reference object? I mean when you create an object in the heap, is it not always passed by reference. Does this have to be explicitly marked as a ref?

Answer 1

Using ref means that the reference is passed to the function.

The default behaviour is that the function receives a new reference to the same object. This means if you change the value of the reference (e.g. set it to a new object) then you are no longer pointing to the original, source object. When you pass using ref then changing the value of the reference changes the source reference – because they are the same thing.

Consider this:

public class Thing
{
    public string Property {get;set;}
}

public static void Go(Thing thing)
{
    thing = new Thing();
    thing.Property = "Changed";
}

public static void Go(ref Thing thing)
{
    thing = new Thing();
    thing.Property = "Changed";
}

Then if you run

var g = new Thing();

// this will not alter g
Go(g);

// this *will* alter g
Go(ref g);