C# Error CS8156 – An expression cannot be used in this context because it may not be passed or returned by reference

C# Error

CS8156 – An expression cannot be used in this context because it may not be passed or returned by reference

Reason for the Error & Solution

An expression cannot be used in this context because it may not be passed or returned by reference

Example

The following sample generates CS8156:

// CS8156.cs (7,27)

class Test
{
    delegate ref int D1();

    void Test1()
    {
        D1 d1 = () => ref 2 + 2;
    }
}

To correct this error

When not using referenceable variables, refactoring to return by value corrects this error:

class Test
{
    delegate int D1();

    void Test1()
    {
        D1 d1 = () => 2 + 2;
    }
}