1.60. C# generics

Generic allows you to delay writing specifications for the data types of programming elements in a class or method until it is actually used in the program. In other words, generics allow you to write a class or method that works with any data type.

You can write the specification of a class or method through alternative parameters of the data type. When the compiler encounters a function call tothe constructor or method of a class, it generates code to handle the specified data type. The following simple example will help you understand this concept:

1.60.1. Example #

using System;
using System.Collections.Generic;
namespace GenericApplication
{
    public class MyGenericArray<T>
    {
        private T[] array;
        public MyGenericArray(int size)
        {
            array = new T[size + 1];
        }
        public T getItem(int index)
        {
            return array[index];
        }
        public void setItem(int index, T value)
        {
            array[index] = value;
        }
    }

    class Tester
    {
        static void Main(string[] args)
        {
            // Declare an integer array
            MyGenericArray<int> intArray = new MyGenericArray<int>(5);
            // Setting values
            for (int c = 0; c < 5; c++)
            {
                intArray.setItem(c, c*5);
            }
            // Get Value
            for (int c = 0; c < 5; c++)
            {
                Console.Write(intArray.getItem(c) + " ");
            }
            Console.WriteLine();
            // Declare a character array
            MyGenericArray<char> charArray = new
MyGenericArray<char>(5);
            // Setting values
            for (int c = 0; c < 5; c++)
            {
                charArray.setItem(c, (char)(c+97));
            }
            // Get Value
            for (int c = 0; c < 5; c++)
            {
                Console.Write(charArray.getItem(c) + " ");
            }
            Console.WriteLine();
            Console.ReadKey();
        }
    }
}

When the above code is compiled and executed, it produces the following results:

0 5 10 15 20
a b c d e

Characteristics of Generic #

Using generics is a technique to enhance the functionality of a program, which is shown in the following aspects:

It helps you maximize code reuse, protect types, and improve performance.
You can create generic collection classes. The .NET framework class library is available in the System.Collections.Generic . The namespace contains some new generic collection classes. You can use these generic collection classes instead of System.Collections .
You can create your own generic interfaces, generic classes, generic methods, generic events, and generic delegates.
You can constrain generic classes to access methods of specific data types.
Information about the types used in generic data types can be obtained at run time by using reflection.

Generic method #

In the above example, we have used generic classes, and we can declare generic methods through type parameters. The following procedure illustratesthis concept:

1.60.2. Example #

using System;
using System.Collections.Generic;
namespace GenericMethodAppl
{
    class Program
    {
        static void Swap<T>(ref T lhs, ref T rhs)
        {
            T temp;
            temp = lhs;
            lhs = rhs;
            rhs = temp;
        }
        static void Main(string[] args)
        {
            int a, b;
            char c, d;
            a = 10;
            b = 20;
            c = 'I';
            d = 'V';
            // Display values before swapping
            Console.WriteLine("Int values before calling swap:");
            Console.WriteLine("a = {0}, b = {1}", a, b);
            Console.WriteLine("Char values before calling swap:");
            Console.WriteLine("c = {0}, d = {1}", c, d);
            // call swap
            Swap<int>(ref a, ref b);
            Swap<char>(ref c, ref d);
            // Display values after swapping
            Console.WriteLine("Int values after calling swap:");
            Console.WriteLine("a = {0}, b = {1}", a, b);
            Console.WriteLine("Char values after calling swap:");
            Console.WriteLine("c = {0}, d = {1}", c, d);
            Console.ReadKey();
        }
    }
}

When the above code is compiled and executed, it produces the following results:

Int values before calling swap:
a = 10, b = 20
Char values before calling swap:
c = I, d = V
Int values after calling swap:
a = 20, b = 10
Char values after calling swap:
c = V, d = I

Generic delegation #

You can define a generic delegate through type parameters. For example:

delegate T NumberChanger<T>(T n);

The following example demonstrates the use of delegates:

1.60.3. Example #

using System;
using System.Collections.Generic;
delegate T NumberChanger<T>(T n);
namespace GenericDelegateAppl
{
    class TestDelegate
    {
        static int num = 10;
        public static int AddNum(int p)
        {
            num += p;
            return num;
        }
        public static int MultNum(int q)
        {
            num *= q;
            return num;
        }
        public static int getNum()
        {
            return num;
        }
        static void Main(string[] args)
        {
            // Create Delegate Instance
            NumberChanger<int> nc1 = new NumberChanger<int>(AddNum);
            NumberChanger<int> nc2 = new NumberChanger<int>(MultNum);
            // Calling methods using delegate objects
            nc1(25);
            Console.WriteLine("Value of Num: {0}", getNum());
            nc2(5);
            Console.WriteLine("Value of Num: {0}", getNum());
            Console.ReadKey();
        }
    }
}

When the above code is compiled and executed, it produces the following results:

Value of Num: 35
Value of Num: 175