C# Generics - Computer Science and Engineering Department

C# Generics - Computer Science and Engineering Department

1. B.Bhuvaneswaran, AP (SG) / CSE
9791519152
[email protected]
C# and .NET Programming
Generics

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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…!