Example of using string constants in a static class in order to use these in the [FunctionName] attribute (activity function) and in the CallActivityAsync() method (orchestration function).

FunctionName.cs

namespace DurableFunctions.Demo.DotNetCore.Basics
{
    public static class FunctionName
    {
        public const string HelloNameActivity = "HelloNameActivity";

        public const string HelloNameOrchestration = "HelloNameOrchestration";
    }
}

HelloNameActivity.cs

namespace DurableFunctions.Demo.DotNetCore.Basics.Activities
{
    public static class HelloNameActivity
    {
        [FunctionName(FunctionName.HelloNameActivity)]
        public static string Run(
            [ActivityTrigger] string name,
            ILogger logger)
        {
            logger.LogInformation($"Name: {name}");

            return $"Hello {name}!";
        }
    }
}