Tim Van Wassenhove

Let me start with a real world example demonstrating the usefulness of a generic DiscreteValuesRange. Imagine that i run a grid computing business and my clients want to book capacity on the grid for a given period. Before their booking is approved, i have to verify that the client has contracts that allow him to use the system for each day of the booking period. Usually, such a check is implemented as following:

bool CheckEachDayIsCovered(Booking booking, Client client)
{
 DateRange periodToCheck = booking.Period;
 DateTime endOfTime = new DateTime(9999, 12, 31);

 DateTime dayToCheck = periodToCheck.Begin;
 while (dayToCheck <= periodToCheck.End)
 {
  bool dayIsCovered = false;

  foreach (Contract contract in client.Contracts)
  {
   if (contract.Period.Includes(dayToCheck))
   {
    dayIsCovered = true;

    if (contract.Period.End < endOfTime)
    {
     dayToCheck = contract.Period.End.AddDays(1);
    }
    else
    {
     return true;
    }
   }
  }

  if (!dayIsCovered)
  {
   return false;
  }
 }

 return true;
}

After a while clients want to buy licenses for only a couple of hours instead of a full day. I realise that my check can remain the same, but that the concept “EndOfTime” has become DateTime(9999, 12, 31, 23, 59, 59) and that i can advance only an hour instead of a day. Since i want to reuse my code i define the IDiscreteValueProvider<T> interface (See Discrete Space):

interface IDiscreteValuesProvider<t>
{
 T GetNextValue(T value);
 T MaxValue { get; }
}

After this i’m able to implement a DiscreteValuesRange<T> that implements the following interface (See: Generic Range):

interface IDiscreteValuesRange<t> : IRange<t>
{
 bool IsCoveredByRanges(IEnumerable<idiscreteValuesRange<t>> ranges);
}

Now, with all this infrastructure i can rewrite my original method as following:

bool CheckEachDayIsCovered(Booking booking, Client client)
{
 return booking.Period.IsCoveredByRanges(client.GetContractPeriods());
}

class Client
{
 ...
 IEnumerable<range<dateTime>> GetContractPeriods()
 {
  foreach (Contract contract in this.Contracts)
  {
   yield return contract.Period;
  }
 }
}

Feel free to download all this infrastructure: DiscreteRange.zip and use it for your next coverage check.