How can I use a modified String in a C# switch → case statement?

Question

I have a string I need to use, a variant of, in many places throughout my application. For example:

String myString = "The Quick Brown Fox";

string someLowerCaseString = myString.ToLower();
string someUpperCaseString = myString.ToUpper();
string someOtherNewString = myString.Replace(' ','+');

I have this String in a Constants.cs file that I reference throughout the application. I have tried two different approaches:

public const String myString = "The Quick Brown Fox";
public static readonly String myString = "The Quick Brown Fox";

However, when I try to "manipulate" the string for use in a switch → case statement, I cannot get it to work:

switch(some_value){
    case Constants.myString.ToLower():
    case Constants.myString.ToUpper():
    case Constants.myString.Replace(' ','+'):
}

I get the error:

CS0426: The type name 'myString' does not exist in the type 'Constants'

I have even tried this:

String localString = Constants.myString.ToLower();
String localString = Constants.myString.ToUpper();
String localString = Constants.myString.Replace(' ','+');
const String localString = Constants.myString.ToLower();
const String localString = Constants.myString.ToUpper();
const String localString = Constants.myString.Replace(' ','+');
switch(some_value){
    case localString:
}

And that does not work either. I get the error:

CS9135: A constant value of type 'string' is expected

I cannot use this:

switch(value.ToLower()){
    // ...
}

As sometimes I need the first letter capitalized and sometimes I need all letters upper/lowercase.

The official Microsoft C# documentation says that these modifying methods return a copy of the string, so I didn't think I was actually manipulating the String constant.

Answer 1

Try this:

using System;

namespace CSharpTests
{
    internal class Constants
    {
        public const String myString = "The Quick Brown Fox";
    }

    internal class Program
    {
        static void Main(string[] args)
        {
            String some_value = Constants.myString.ToLower();
            
            switch (some_value)
            {
                case string s when s == Constants.myString.ToUpper():
                    Console.WriteLine("Is upper");
                    break;
                case string s when s == Constants.myString.ToLower():
                    Console.WriteLine("Is lower");
                    break;
                case string s when s == Constants.myString.Replace(' ', '_'):
                    Console.WriteLine("Is replaced");
                    break;
                default:
                    Console.WriteLine("None of the cases");
                    break;
            }
        }
    }
}