C# Error CS0283 – The type ‘type’ cannot be declared const

C# Compiler Error

CS0283 – The type ‘type’ cannot be declared const

Reason for the Error

You’ll get this error in your C# code when you are using a const declaration on type that is not supported. In C#, const declaration can only be applied on specified primitive data types, enums and any reference types that is assigned a value of null.

For example, lets try to compile the below code snippet.

using System;

namespace DeveloperPublishNamespace
{
    public class Employee
    {
    }
    class Program
    {
        const Employee emp = new Employee();
        static void Main(string[] args)
        {
            Console.WriteLine("Hello World!");
        }
    }
}

You’ll receive the error code CS0283 because you are declaring a const objext of type “Employee” by creating an instance. Note that this is a reference type and you are declaring it as constant. This will also result in another error code CS0133.

Error CS0283 The type ‘Employee’ cannot be declared const DeveloperPublish C:\Users\Senthil\source\repos\ConsoleApp4\ConsoleApp4\Program.cs 10 Active

You will receive an different error code as shown below depending on the version of C# that you are running.

CS01344 – Main.cs(10,30): error CS0134: A constant “DeveloperPublishNamespace.Program.emp’ of reference type `DeveloperPublishNamespace.Employee’ can only be initialized with null

Solution

You can fix this error in your C# program by simply changing the const to readonly during your declaration.

using System;

namespace DeveloperPublishNamespace
{
    public class Employee
    {
    }
    class Program
    {
        readonly Employee emp = new Employee();
        static void Main(string[] args)
        {
            Console.WriteLine("Hello World!");
        }
    }
}