How can you use optional parameters in C#?

Question

^{Note: This question was asked at a time when C# did not yet support optional parameters (i.e. before C# 4).}

We\'re building a web API tha

Answer 1

In the case when default values aren't available the way to add an optional parameter is to use .NET OptionalAttribute class - https://docs.microsoft.com/en-us/dotnet/api/system.runtime.interopservices.optionalattribute?view=netframework-4.8

Example of the code is below:

namespace OptionalParameterWithOptionalAttribute
{
    class Program
    {
        static void Main(string[] args)
        {
            //Calling the helper method Hello only with required parameters
            Hello("Vardenis", "Pavardenis");
            //Calling the helper method Hello with required and optional parameters
            Hello("Vardenis", "Pavardenis", "Palanga");
        }
        public static void Hello(string firstName, string secondName, 
            [System.Runtime.InteropServices.OptionalAttribute] string  fromCity)
        {
            string result = firstName + " " + secondName;
            if (fromCity != null)
            {
                result += " from " + fromCity;
            }
            Console.WriteLine("Hello " + result);
        }

    }
}