Question

Possible Duplicate:
When to pass ref keyword in

Hi All,

I am just surprised that why we have ref in C# while by default everything which is a reference type in C# is passed as a reference.

In simpler words, can anyone explain me the difference between these two method calls:

public void Test(SomeClass someClass)
{
  // some code here
} 

and

public void Test(ref SomeClass someClass)
{
  // some code here
}

In my thinking they both have reference to same memory location.

So why do we need ref keyword at all ?

Answer 1

When you pass an object you pass it by reference. This means that anything you do to that object will be reflected in the object after the method returns. When you pass the reference by reference i.e. void Foo(ref object obj) you are passing the address of that object. You can then re-assign the address to a different object and that will be the state of things when the method returns

foo (object o)
{
   ...
}

var v = new object();
foo(v);

v will still reference the same object that was instantiated prior to the call to foo

void bar(ref object o)
{
   o = null;
}

var v = new object();
foo(ref v);
// v is now null