Why Doesn't Assigning a Reference Parameter to a Class Field Maintain the Reference in C#?

Referencing Class Fields in C#

In C#, passing a parameter by reference allows for direct modification of the original variable. However, when assigning a reference parameter to a class field, the expected behavior may not occur.

Consider the following code:

public class X
{
    public X()
    {
        string example = "X";

        new Y(ref example);
        new Z(ref example);

        System.Diagnostics.Debug.WriteLine(example);
    }
}

public class Y
{
    public Y(ref string example)
    {
        example += " (Updated By Y)";
    }
}

public class Z
{
    private string _Example;

    public Z(ref string example)
    {
        this._Example = example;
        this._Example += " (Updated By Z)";
    }
}

var x = new X();

Upon execution, the output is "X (Updated By Y)", not "X (Updated By Y) (Updated By Z)" as anticipated.

This is because assigning a reference parameter to a class field breaks the reference. To maintain the reference, a solution is to use a getter and setter:

sealed class Ref<T>
{
    private readonly Func<T> getter;
    private readonly Action<T> setter;
    public Ref(Func<T> getter, Action<T> setter)
    {
        this.getter = getter;
        this.setter = setter;
    }
    public T Value { get { return getter(); } set { setter(value); } }
}

Ref<int> x;
void M()
{
    int y = 123;
    x = new Ref<int>(() => y, z => { y = z; });
    x.Value = 456;
    Console.WriteLine(y); // 456 -- setting x.Value changes y.
}

In this example, 'x' is an object that can get and set the value of 'y', maintaining the reference between them. Note that while ref locals and ref-returning methods are supported in the CLR, they are not yet available in C#.

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