C# Error CS0192 – Fields of static readonly field ‘name’ cannot be passed ref or out (except in a static constructor)

C# Compiler Error

CS0192 – Fields of static readonly field ‘name’ cannot be passed ref or out (except in a static constructor)

Reason for the Error

You will receive this error when you have declared a field as readonly and you try to pass the readonly field to a ref or out parameter outside of constructor in your C# code.

For example, try to compile the below code snippet.

namespace DeveloperPubNamespace
{
    class Employee
    {
        public readonly int Id;
        static void SetId(ref int refId)
        {
            refId = 0;
        }
        public void InitializeEmployee()
        {
            SetId(ref Id);   // CS0192  
        }
    }
    class Program
    {      
        static void Main(string[] args)
        {

        }    
    }
  
}

The above code snippet will result with the C# error code CS0192 because Id is a readonly field is been passed to the ref parameter of the SetId function.

Error CS0192 A readonly field cannot be used as a ref or out value (except in a constructor) ConsoleApp3 C:\Users\SenthilBalu\source\repos\ConsoleApp3\ConsoleApp3\Program.cs 12 Active

Solution

To fix the error, ensure that the readonly fields are not passed to the ref or out parameter to functions in your C# code. You can however pass the readonly field to out or ref parameter inside constructor.

Below is a sample code snippet demonstrating how to fix the error code CS0191.

namespace DeveloperPubNamespace
{
    class Employee
    {
        public readonly int Id;
        static void SetId(ref int refId)
        {
            refId = 0;
        }
        public Employee()
        {
            SetId(ref Id);   
        }
    }
    class Program
    {
        static void Main(string[] args)
        {

        }
    }

}