C# – Indexers Using String as an Index

Prerequisite: Properties in C#

Indexers allow instances of a class or struct to be indexed just like arrays. By using indexers class will behave like a virtual array. The indexed value can be set or retrieved without explicitly specifying a type or instance member. Indexers resemble properties except that their accessors take parameters. Indexers are almost similar to the Properties. The main difference between Indexers and Properties is that the accessors of the Indexers will take parameters.

Indexers using a string as an index:

This method will give you more information, readability. If we want to retrieve information using a string as an index.

Example:

ic["username"] = "user12";  
ic["password"] = "12345";  

This will give more readability than the code given below.

ic[0] = "user12";  
ic[1] = "12345";  

Syntax:

[access_modifier] [return_type] this [argument_list]
{
 get  
 {
    // retrieval code or code to get the value 
 }
 set  
 {
   // code for setting value to member
 }

In the above syntax:

• access_modifier: It can be public, private, protected, or internal.
• return_type: It can be any valid C# type. In this case, it will be of string type.
• this: It is the keyword which points to the object of the current class.
• argument_list: This specifies the parameter list of the indexer.
• get{ } and set { }: These are the accessors.

Example:

C#

// C# program to illustrate the Indexers
// Using String as an Index
using System;

// class declaration
class IndexerPOC
{

    // class members
    private string[] val = new string[4];

    // indexer array
    private string[] indices={"username","password","email","Book"};

    // Indexer declaration
    // Here public is the modifier
    // string is the return type of
    // Indexer and "this" is the keyword
      // which refer to the calling object.
    // having parameters list
    public string this[string index]
    {

        // get Accessor
        // retrieving the values
        // stored in val[] array
        // of strings using string indexer.
        get
        {

            return val[Array.IndexOf(indices,index)];
        }

        // set Accessor
        // setting the value at
        // passed i of val
        set
        {

            // value keyword is used
            // to define the value
            // being assigned by the
            // set indexer.
            val[ Array.IndexOf(indices,index)] = value;
        }
    }
}

// Driver Class
class Program {

    // Main Method
    public static void Main() {

        // creating an object of parent class which
        // acts as primary address for using Indexer
        IndexerPOC ic = new IndexerPOC();

        // Inserting values in ic[]
        // Here we are using the object
        // of class as an array
        ic["username"] = "user12";
        ic["password"] = "12345";
        ic["email"] = "user123@gmail.com";
        ic["Book"]="CSHARP";
        Console.Write("Printing values stored in objects used as arrays\n");

        // printing values
        Console.WriteLine("UserName = {0}", ic["username"]);
        Console.WriteLine("Password = {0}", ic["password"]);
        Console.WriteLine("Email = {0}", ic["email"]);
        Console.WriteLine("Book = {0}", ic["Book"]);

    }
}

Output:

Printing values stored in objects used as arrays
UserName = user12
Password = 12345
Email = user123@gmail.com
Book = CSHARP