C# String reference type passed as copy?

Question

I have this doubt related to C# "String" reference types .

The following code:

string s = "lana del rey" 
string d = s;
s = "elvis presley";
Console.Writeline(d);

Why the Output is not "elvis presley" ? If d is pointing to the same memory location of s ?

Could you please explain this?

A more detailed explanation of my initial question:

All your answers were very useful. That question came to me with this common code sample frecuently used to explain difference between value types and reference types:

class Rectangle
{
    public double Length { get; set; }
}

struct Point 
{
    public double X, Y;
}

Point p1 = new Point();
p1.X = 10;
p1.Y = 20;
Point p2 = p1;
p2.X = 100;
Console.WriteLine(“p1.X = {0}”, p1.X);

Rectangle rect1 = new Rectangle
{ Length = 10.0, Width = 20.0 };
Rectangle rect2 = rect1;
rect2.Length = 100.0;
Console.WriteLine(“rect1.Length = {0}”,rect1.Length);

In this case, the second Console.WriteLine statement will output: “rect1.Length = 100”

In this case class is reference type, struct is value type. How can I demostrate the same reference type behaviour using a string ?

Thanks in advance.

Answer 1

It has nothing to do with mutability

string s = "lana del rey" 
string d = s;

Here 2 variables s and d refer to the same object in memory.

s = "elvis presley";

here in the right part of the statement the new object is allocated and initialized with "elvis presley" and assigned to s. So now s refers to another object. And while we haven't change the d reference value - it continues referring to the "lana del rey" as it originally did.

Now the real life analogy:

There are 2 people (A and B) pointing using their fingers to a building far away. They are independent to each other, and don't even see what another is pointing to. Then A decides to start pointing to another building. As long as they aren't connected to each other - now A points to another building, and B continues pointing to the original building (since no one asked them to stop doing that)

PS: what you probably are confusing is the concept behind a pointer and a reference. Not sure if it makes sense to explain it here since you might be confused even more. But now at least you might google for the corresponding keywords.