C# Error CS1601 – Cannot make reference to variable of type ‘{0}’

C# Error

CS1601 – Cannot make reference to variable of type ‘{0}’

Reason for the Error & Solution

Method or delegate parameter cannot be of type ‘type’

Some types in the .NET class library, for example, , and cannot be used as , or parameters because they could potentially be used to perform unsafe operations.

The following sample generates CS1601:

// CS1601.cs  
using System;

class MyClass
{
    public void Test1(in TypedReference t)   // CS1601  
    {
    }

    public void Test2(ref TypedReference t)   // CS1601  
    {
    }

    public void Test3(out ArgIterator t)   // CS1601  
    {
        t = default;
    }
}