Deciding between interfaces and concrete classes

In this section, we will show that declaring a collection using an interface declaration rather than a concrete class declaration provides better time-based performance. We will accomplish this by benchmarking the generation of collections using an IList interface, as well as by using a List concrete class, so that you can see the difference in the performance of the different approaches. Follow these steps:

1. In the CH06_Collections project, add a new folder called ConcreteVsInterface.
2. In the ConcreteVsInterface folder, add the ITax interface:

   internal interface ITax
   {
         int Id { get; set; }
         TaxType TaxType { get; set; }
         TaxRate TaxRate { get; set; }
         decimal LowerLimit { get; set; }
         decimal UpperLimit { get; set; }
         ...