Is this the best way to represent decades with TimeSpan?

Question

I'm making a graph that cover "1930-1940", "1940-1950", "1950-1960", "1960-1970", ...

I want to represent this with a DateTime and a Timespan, but I'm not really sure how to make the TimeSpan, and I find it hard to verify if my timespans are correct.

Is this how I should use TimeSpan, or does it overlap? If it's overlapning then how can I fix it?

List<DateTime> list1 = new List<DateTime>();
List<TimeSpan> list2 = new List<TimeSpan>();

int startYearInt = 1930;

int times = 0;
const int intervalSize = 10;
for (int i = startYearInt; i < 2020; i += intervalSize)
{
    DateTime sYear = new DateTime(startYearInt + (intervalSize * times++), 1, 1);
    TimeSpan period = (sYear.AddYears(intervalSize)) - sYear;

    list1.Add(sYear);
    list2.Add(period); // <<-- Don't know if if this is correct?
}

EDIT: I have this too. And if My timespan is too small or to last it can give some problems.

public bool IsInsidePeriod(DateTime dt)
{
    return dt >= FromYearDateTime && dt < FromYearDateTime.Add(periodTimeSpan);
}

Answer 1

You're better off creating a DateRange value type than using a DateTime and a TimeSpan like that. Look here for an example. You can then have a factory method that gives you a range for a decade: DateRange.DecadeStartingOn(1930);. This way, you raise the level of abstraction and deal with the concepts you're referring to in the code itself.

Your IsInsidePeriod is a simple operation for the DateRange:

public bool Includes(DateTime date) {
  return start <= date && date <= end;
}

(assuming both start and end are inclusive)

Now, if you only need to deal with decades, you don't really need a full DateRange class, just this:

class Decade {

  public int StartYear { get; private set; }
  public int EndYear { get { return StartYear + 9; } }

  public Decade(int startYear) {
    StartYear = startYear;
  }

  public bool Includes(DateTime date) {
    return StartYear <= date.Year && date.Year <= EndYear;
  }

  public override string ToString() {
    return string.Format("{0}-{1}", StartYear, EndYear + 1);
  }

}

Or maybe a more general YearRange.