C# in Depth

70 CHAPTER 3 Parameterized typing with generics}{}: IEnumerablepublic Dictionary(){[...]}Declaresparameterlessconstructorpublic void Add (TKey key, TValue value){[...]}public TValue this [TKey key]{get { [...] }set { [...] }}public bool ContainsValue (TValue value){[...]}public bool ContainsKey (TKey key){[...]}[... other members ...]Implementsgeneric interfaceDeclares methodusing typeparametersNotice how Dictionary implements the generic interface IEnumerable (and many other interfaces in real life). Whatever typearguments you specify for the class are applied to the interface where the same typeparameters are used—so in our example, Dictionary implementsIEnumerable. Now that’s actually sort of a “doublygeneric” interface—it’s the IEnumerable interface, with the structure KeyValue-Pair as the type argument. It’s because it implements that interface thatlisting 3.1 was able to enumerate the keys and values in the way that it did. It’s also worthpointing out that the constructor doesn’t list the type parameters in angle brackets. Thetype parameters belong to the type rather than to the particular constructor, so that’swhere they’re declared.Generic types can effectively be overloaded on the number of type parameters—soyou could define MyType, MyType, MyType, MyType, and so forth, allwithin the same namespace. The names of the type parameters aren’t used when consideringthis—just how many there are of them. These types are unrelated except inname—there’s no default conversion from one to another, for instance. The same istrue for generic methods: two methods can be exactly the same in signature otherthan the number of type parameters.Licensed to Rhona Hadida