The document provides an overview of generics in C# programming, explaining the concept of generic classes, methods, and constraints. It highlights how generics enable type-safety, code reuse, and performance by allowing users to define classes and methods with type parameters. Additionally, examples illustrate how to create and utilize generic classes and methods, along with applying constraints to restrict the types that can be used.

1. B.Bhuvaneswaran, AP (SG) / CSE
9791519152
bhuvaneswaran@rajalakshmi.edu.in
C# and .NET Programming
Generics

2. Generics Rajalakshmi Engineering College 2
Introduction
▪ Generic class is a class, which contains one or more "type
parameters".
▪ You must pass any data type (standard data type / structure /
class), while creating object for the generic class.

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Generic Class - Example
class ClassName<T>
{
public T FieldName;
}

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Object of Generic Class - Example
▪ ClassName<int> referenceVariable = new ClassName<int> ( );

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Explanation
▪ The same field may belong to different data types, w.r.t. different objects of the
same class.
▪ You will decide the data type of the field, while creating the object, rather than
while creating field in the class.
▪ It helps you in code reuse, performance and type-safety.
▪ You can create your own generic-classes, generic-methods, generic-interfaces
and generic-delegates.
▪ You can create generic collection classes. The .NET framework class library
contains many new generic collection classes in System.Collections.Generic
namespace.
▪ The generic type parameter (T) acts as "temporary data type", which represents
the actual data type, provided by the user, while creating object.
▪ You can have multiple "generic type parameters" in the same class (for use for
different fields.
▪ Generics are introduced in C# 2.0.

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Generic Classes-Program
//Generic class
public class User<T1>
{
//generic field
public T1 RegistrationStatus;
}
class Program
{
static void Main()
{
//create object of generic class
User<int> user1 = new User<int>();
User<bool> user2 = new User<bool>();
//set value into generic field
user1.RegistrationStatus = 1234;
user2.RegistrationStatus = false;
System.Console.WriteLine(user1.RegistrationStatus);
System.Console.WriteLine(user2.RegistrationStatus);
System.Console.ReadKey();
}
}

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Multiple Generic Parameters-Program
//Generic class
public class User<T1, T2>
{
//generic field
public T1 RegistrationStatus;
//another generic field
public T2 Age;
}
class Program
{
static void Main()
{
//create object of generic class
User<int, int> user1 = new User<int, int>();
User<bool, string> user2 = new User<bool, string>();
//set value into generic field
user1.RegistrationStatus = 1234;
user2.RegistrationStatus = false;
user1.Age = 22;
user2.Age = "35 - 40";
System.Console.WriteLine(user1.RegistrationStatus);
System.Console.WriteLine(user2.RegistrationStatus);
System.Console.WriteLine(user1.Age);
System.Console.WriteLine(user2.Age);
System.Console.ReadKey();
}
}

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Generic Constraints
▪ Generic Constraints are used to specify the types allowed to be
accepted in the "generic type parameter".
• where T : class
• where T : struct
• where T : ClassName
• where T : InterfaceName
• where T : new( )

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Generic Constraints - Example
class ClassName<T> where T : class
{
public T FieldName;
}

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Object of Generic Class - Example
▪ ClassName<int> referenceVariable = new ClassName<int> ( ); //error

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Understanding Generic Constraints
▪ Advantage
• You can restrict what type of data types (class names) allowed to be passed
while creating object.
▪ In C#, constraints are used to restrict a generics to accept only
particular type or its derived types.
▪ By using 'where' keyword, we can apply constraints on generics.
▪ You can apply multiple constraints on generic classes or methods
based on your requirements.
▪ Eg: where T : class where T2 : class

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Generic Constraint - Program
public abstract class Student
{
public abstract int Marks { get; set; }
}
public class GraduateStudent : Student
{
public override int Marks { get; set; }
}
public class PostGraduateStudent : Student
{
public override int Marks { get; set; }
}
//generic class with constraints (want to accept Student or its child classes only)
public class MarksPrinter<T> where T : Student
{
public T stu;
public void PrintMarks()
{
Student temp = (Student)stu;
System.Console.WriteLine(temp.Marks);
}
}
class Program
{
static void Main()
{
//create object of generic class
MarksPrinter<GraduateStudent> mp = new MarksPrinter<GraduateStudent>();
mp.stu = new GraduateStudent() { Marks = 80 };
mp.PrintMarks();
System.Console.ReadKey();
}
}

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Generic Methods
▪ Generic Method is a method that has one or more generic
parameter(s).
▪ You can restrict what type of data types to be allowed to be
passed to the parameter while calling the method.

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Generic Method – Example
public void MethodName<T>
{
}

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Calling Generic Method - Example
▪ MethodName<datatype>( valueHere );

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Generic Methods - Class
public class Employee
{
public int Salary;
}
public class Student
{
public int Marks;
}
//a class with generic method
public class Sample
{
//generic method
public void PrintData<T>(T obj) where T : class
{
if (obj.GetType() == typeof(Student))
{
Student temp = obj as Student;
System.Console.WriteLine(temp.Marks);
}
else if (obj.GetType() == typeof(Employee))
{
Employee temp = obj as Employee;
System.Console.WriteLine(temp.Salary);
}
}
}

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Generic Methods - Program
class Program
{
static void Main()
{
//create objects
Sample sample = new Sample();
Employee emp = new Employee() { Salary = 1000 };
Student stu = new Student() { Marks = 80 };
//call the generic method
sample.PrintData<Employee>(emp);
sample.PrintData<Student>(stu);
System.Console.ReadKey();
}
}

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Assignment
1. What are generic classes in C#? Provide an example of how to define
and use a generic class.
2. What are generic methods in C#? Provide an example of how to define
and use a generic method.
3. What are generic constraints in C#? Why are they important?
4. Can you provide an example of using generic constraints in a real-world
project scenario?
5. How can you specify multiple generic constraints for a type parameter
in C#?
6. What is the purpose of the default keyword in generic constraints?
7. Can you explain the concept of type inference in C# with respect to
generic methods?

19. Queries?

20. Thank You…!