C# | Generics – Introduction

Generic is a class which allows the user to define classes and methods with the placeholder. Generics were added to version 2.0 of the C# language. The basic idea behind using Generic is to allow type (Integer, String, … etc and user-defined types) to be a parameter to methods, classes, and interfaces. A primary limitation of collections is the absence of effective type checking. This means that you can put any object in a collection because all classes in the C# programming language extend from the object base class. This compromises type safety and contradicts the basic definition of C# as a type-safe language. In addition, using collections involves a significant performance overhead in the form of implicit and explicit type casting that is required to add or retrieve objects from a collection.
To address the type safety issue, the .NET framework provides generics to create classes, structures, interfaces, and methods that have placeholders for the types they use. Generics are commonly used to create type-safe collections for both reference and value types. The .NET framework provides an extensive set of interfaces and classes in the System.Collections.Generic namespace for implementing generic collections.

Generic Class

Generics in C# is its most powerful feature. It allows you to define the type-safe data structures. This out-turn in a remarkable performance boost and high-grade code, because it helps to reuse data processing algorithms without replicating type-specific code. Generics are similar to templates in C++ but are different in implementation and capabilities. Generics introduces the concept of type parameters, because of which it is possible to create methods and classes that defers the framing of data type until the class or method is declared and is instantiated by client code. Generic types perform better than normal system types because they reduce the need for boxing, unboxing, and type casting the variables or objects.
Parameter types are specified in generic class creation.

To create objects of generic class, following syntax is used:

BaseType  obj = new BaseType ()

Example:

// C# program to show working of
// user defined Generic classes
using System;

// We use < > to specify Parameter type
public class GFG<T> {

    // private data members
    private T data;

    // using properties
    public T value
    {

        // using accessors
        get
        {
            return this.data;
        }
        set
        {
            this.data = value;
        }
    }
}

// Driver class
class Test {

    // Main method
    static void Main(string[] args)
    {

        // instance of string type
        GFG<string> name = new GFG<string>();
        name.value = "GeeksforGeeks";

        // instance of float type
        GFG<float> version = new GFG<float>();
        version.value = 5.0F;

        // display GeeksforGeeks
        Console.WriteLine(name.value);

        // display 5
        Console.WriteLine(version.value);
    }
}

Output :

GeeksforGeeks
5

Explanation: The preceding example defines a generic class, GFG, which uses a generic type parameter ‘T’. In the Main() method, two instances of GFG have been created by replacing ‘T’ with ‘string’ and ‘float’ data types. These objects are used to store ‘string’ and ‘float’ values respectively. The GFG class ensures type safety by accepting the required type in its constructor.

A Generic method with various parameters: Just as a method can take one argument, generics can take various parameters. One argument can be passed as a familiar type and other as a generic type, as shown below :

• Example:

  // C# program to show multiple
  // type parameters in Generics
  using System;
  
  public class GFG {
  
      // Generics method
      public void Display<TypeOfValue>(string msg, TypeOfValue value)
      {
          Console.WriteLine("{0}:{1}", msg, value);
      }
  }
  
  // Driver class
  public class Example {
  
      // Main Method
      public static int Main()
      {
  
          // creating object of class GFG
          GFG p = new GFG();
  
          // calling Generics method
          p.Display<int>("Integer", 122);
          p.Display<char>("Character", 'H');
          p.Display<double>("Decimal", 255.67);
          return 0;
      }
  }

  Output :

  Integer:122
  Character:H
  Decimal:255.67
  

Features of Generics

Generics is a technique that improves your programs in many ways such as:

• It helps you in code reuse, performance and type safety.
• You can create your own generic classes, methods, interfaces and delegates.
• You can create generic collection classes. The .NET framework class library contains many new generic collection classes in System.Collections.Generic namespace.
• You can get information on the types used in generic data type at run-time.

Advantages of Generics

• Reusability: You can use a single generic type definition for multiple purposes in the same code without any alterations. For example, you can create a generic method to add two numbers. This method can be used to add two integers as well as two floats without any modification in the code.
• Type Safety: Generic data types provide better type safety, especially in the case of collections. When using generics you need to define the type of objects to be passed to a collection. This helps the compiler to ensure that only those object types that are defined in the definition can be passed to the collection.
• Performance: Generic types provide better performance as compared to normal system types because they reduce the need for boxing, unboxing, and typecasting of variables or objects.