The ICollection and IList Interfaces

Although the enumeration interfaces provide a protocol for forward-only iteration over a collection, they don’t provide a mechanism to determine the size of the collection, access a member by index, search, or modify the collection. For such functionality, the .NET Framework defines the ICollection, IList, and IDictionary interfaces. Each comes in both generic and nongeneric versions; however, the nongeneric versions exist mostly for legacy support.

The inheritance hierarchy for these interfaces was shown in Figure 7-1. The easiest way to summarize them is as follows: