Why Doesn't C# Allow Fields to Hold References, and What Are the Alternatives?

Reference Assignments in C# Class Fields

In C#, attempting to assign by "reference" to a class field may result in unexpected behavior. 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();

The expected output is "X (Updated By Y) (Updated By Z)", but instead, only "X (Updated By Y)" is printed. This behavior occurs because assigning a "ref parameter" to a field loses the reference.

Why Can't Fields Hold References?

There are only three possible options when considering fields of "ref type":

1. Disallow fields of ref type: This is the current behavior in C#.
2. Allow unsafe fields of ref type: This would allow for the possibility of accessing unsafe memory, potentially leading to unpredictable behavior.
3. Store local variables outside the stack: This would prevent the optimization of storing local variables in a temporary memory pool, which is not desirable.

Option 1 was chosen to ensure program stability and prevent the creation of time bombs in the code.

How to Achieve Reference-Like Behavior

While you cannot have fields of ref type, there are alternative ways to achieve reference-like behavior:

• Creating a class that encapsulates the reference: You can create a class that provides getter and setter methods to access and modify the referenced variable. This is an indirect way of referencing another variable.
• Using C# 7 features (Ref Locals and Ref Returning Methods): Although C# does not support storing references in fields, it does support ref locals and ref returning methods. This allows you to create ref variables that can be passed by reference and modified by multiple methods.

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