This document discusses .NET generics. It explains that generics allow creating reusable class and method templates that can work with different data types. This avoids duplicate code and provides type safety. Some key points made: - Generics use placeholders like <T> for type parameters to make classes and methods reusable for multiple types. - The .NET Base Class Library enhanced generics support with collections like List<T> and interfaces like IEnumerable<T>. - Constraints can be applied to generic types using "where" to restrict them to implement particular interfaces. This provides type safety.

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document of baabtra –Mentoring Partner
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Ltd

3. .NET Generics

4. Generics
• Using Generics, we can create class templates that
support any type.
• Compile-time type checking
– By creating a generic class, you can create a collection that
is type-safe at compile-time.
– There is no need to write code to test for the correct data
type, because it is enforced at compile time
– The need for type casting and the possibility of run-time
errors are reduced.
• Binary code reuse
– Reuse same code with multiple types
– Generic code generated at run-time!
run-time

5. • Generics are classes, structures, interfaces, and
methods that have placeholders (type parameters)
for one or more of the types that they store or use.
• A generic collection class might use a type parameter
as a placeholder for the type of objects that it stores
• improved performance
• reduced code

6. simple generic class definition
•
public class Generic<T>
{
public T Field;
}
public static void Main()
{
Generic<string> g = new Generic<string>();
g.Field = "A string";
Console.WriteLine("Generic.Field = "{0}"", g.Field);
Console.WriteLine("Generic.Field.GetType() = {0}", g.Field.GetType().FullName);
}

7. Define and use a generic method
public class Method<T>
{
T[] item;
public void Test(T item)
{...}
}
Method<int> Test= new Method<int>();

8. Placeholders for Generic Types
• ƒ T…type
• ƒ K…key
• ƒ V…value

9. Applying Generics
• Generics may have any # of type parameters
Class Node<K, T>
{ public Node(K key, T item, Node<K, T>nextNode {….}
private K Key;
private T Item;
private Node<k, T> NextNode; }
• Must then instantiate with the # of parameters

10. Generic Interfaces
public interface ICalculator<T>
{
T Add(T param1, T param2);
}
public class SamCalculator : ICalculator<int>
{
public int Add(int arg1, int ar2)
{ return arg1 + arg2; }
}
• Interface declared with type parameters = a generic interface
declaration

11. Derivation Constraints
• Where reserved word to define a constraint
• Use where on generic type parameter followed by derivation
colon indicating generic type parameter implements
particular interface
public class LinkedList<K, T> where K : IComparable
• Overcome by new generic interface IComparable<T> in
System.Collections.Generics
• Constrain plus new interface eliminates boxing penalty:
public class LinkedList<K, T> where K : IComparable<K>

12. Derivation Constraints
• All constraints must appear after actual derivation list of
generic class
• Ex: If LinkedList<T> derives from IEnumerable<T>, put where
keyword after it:
public class LinkedList<K,T> : IEnumerable<T> where K :
IComparable<K>
• Can provide constraints for every generic type parameter
public class LinkedList<K, T> where K : IComparable<K>
where T : IClonable

13. Constructor Constraints
• Suppose want to instantiate new generic object inside generic
class
– C# compiler doesn’t know whether specific type you are going to use
has matching public default constructor
– Will not compile
• Constructor constraint makes possible for generic code to
create instances of type specified by constraining type args to
types that implement public default constructor
• Only default or parameterless constructors supported

14. Using Generics in the BCL

15. Enhancing the Base Library
Generic Collections
• System.Collections.Generic classes
–
–
–
–
–
List<T>
LinkedList<T>
Dictionary<K, V>
Stack<T>
Queue<T>
// new in Beta1!
// equivalent to non-generic HashTable
• System.Collections.Generic interfaces
–
–
–
–
–
–
–
IList<T>
IDictionary<K, V>
ICollection<T>
IEnumerable<T>
IEnumerator<T>
IComparable<T>
IComparer<T>
// replacement for IList
// replacement for IDictionary
// replacement for ICollection
// replacement for IEnumerable
// replacement for IEnumerator
// replacement for IComparable
// replacement for IComparer

16. Using Generics in the BCL
• All generic collections implement generic IEnumerable<T>
interface
• IEnumerable<T> provides access to IEnumerator<T> Iterators
interface, for abstracted iterations over collections (Think C++
STL Iterators)
Public interface IEnumerable<T>
{ IEnumerator<T> GetEnumerator(); }
Public interface IEnumerator<T> : IDisposable
{ T Current {get;}
bool MoveNext(); }

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