String object is really by reference? [duplicate]

Answer 1

Strings are references.

changeMe doesn't change the string, it just reassigns a local reference (pointer) within that function.

Now, if you passed the string as a ref arg, you can have more fun:

public static string changeMe(ref string param) {
    param = "I have changed you!!!";
    return ""; // no return for test
}

Answer 2

Yes, this seems strange. What's happening is that you're passing a reference to your string in the parameter, but you're passing it by value, i.e. you're creating a copy of the reference in the parameter. So when you reassign it within the scope of you're function, you're only changing the changeMe() method's local copy of your string reference.

Lots more info about this here: http://www.yoda.arachsys.com/csharp/parameters.html

Answer 3

For all other reference types, passing it using byval semantics (without ref or out ), means you cannot change which object on the heap the callers copy points to, it does not mean you can't change the contents of the object on the heap that the variable points to. Because strings are immutable, they are truly an exception, they behave like a value type in this respect, even though they are a reference type, but this is done by exceptional additional coding in the CLR.

Answer 4

strings are indeed a special case. They are a reference type but behave like value types. This was done for "simplicity's sakes" by the .Net development team.

Great quote: It is a reference type It's a common misconception that string is a value type. That's because its immutability (see next point) makes it act sort of like a value type. It actually acts like a normal reference type. See my articles on parameter passing and memory for more details of the differences between value types and reference types.

From: http://www.yoda.arachsys.com/csharp/strings.html

Answer 5

You passed by value and made a copy of the reference. Pass it by reference it will change. Well, really a new string will be created and your reference will be to a new spot.

Answer 6

String is indeed a reference type. However, when your Main method calls changeMe(str), .NET passes a copy of the reference to str to changeMe in the param argument. changeMe then modifies this copy to refer to "I have changed you!!!", but the original str reference still points to "I will never change".

Being a reference type means that if you changed the state of the passed string, the caller would see those changes. (You can't do this to a string because strings are immutable, but you can do it to other reference types e.g. Control.) But reassigning a parameter doesn't change the value the caller passed in that parameter, even if that value is a reference.