C#-How to use empty List<string> as optional parameter

Question

Can somebody provide a example of this?

I have tried null,string.Empty and object initialization but they don't work since default value has to be constant at compile time

Answer 1

Just use the null coalescing operator and an instance of empty List<string>

public void Process(string param1, List<string> param2 = null)  {     param2 = param2 ?? new List<string>();      // or starting with C# 8     param2 ??= new List<string>(); } 

The problem with this is that if "param2" is null and you assign a new reference then it wouldn't be accessible in the calling context.

Answer 2

You may also do the following using default which IS a compile-time-constant (null in the case of a List<T>):

void DoSomething(List<string> lst = default(List<string>))  {     if (lst == default(List<string>)) lst = new List<string>(); }