using System;
using System.Collections.Generic;

struct RosterLine {
    public string RosCd;
    public string ActCd;
    public double Hrs;
}

public class Test
{
	public static void Main()
	{
		// your code goes here
		var dict = new SortedDictionary<DateTime, RosterLine>();
		dict.Add(DateTime.Today, new RosterLine());
		// Does not work as RosterLine is a value type
		dict[DateTime.Today].ActCd = "SO";
		// Works, but means a lot of copying
		var temp = dict[DateTime.Today];
		temp.ActCd = "SO";
		dict[DateTime.Today] = temp;
	}
}