Multi-parameter indexers in C Sharp (C#)

Introduction

Multi-parameter indexers let you access data using more than one key, like looking up a value by row and column in a table.

When you want to access elements in a grid or matrix using two numbers.

When you have a collection that needs two keys to find an item, like a calendar with year and month.

When you want to simplify code that uses multiple keys to get or set values.

When you want to make your class behave like a 2D array or table.

Syntax

C Sharp (C#)

public returnType this[type1 index1, type2 index2]
{
    get { /* return value based on index1 and index2 */ }
    set { /* set value based on index1 and index2 */ }
}

The keyword this defines the indexer.

You can use any number of parameters separated by commas inside the square brackets.

Examples

Indexer for a 2D integer matrix using row and column.

C Sharp (C#)

public int this[int row, int col]
{
    get { return matrix[row, col]; }
    set { matrix[row, col] = value; }
}

Indexer that looks up a person by first and last name.

C Sharp (C#)

public string this[string firstName, string lastName]
{
    get { return FindPerson(firstName, lastName); }
}

Sample Program

This program creates a 3x3 table and sets values at two positions using the multi-parameter indexer. Then it prints those values.

C Sharp (C#)

using System;

class Table
{
    private int[,] data = new int[3, 3];

    public int this[int row, int col]
    {
        get { return data[row, col]; }
        set { data[row, col] = value; }
    }
}

class Program
{
    static void Main()
    {
        Table table = new Table();
        table[0, 0] = 10;
        table[1, 2] = 20;
        Console.WriteLine(table[0, 0]);
        Console.WriteLine(table[1, 2]);
    }
}

Important Notes

Multi-parameter indexers make your class easier to use when working with multi-key data.

Indexers can have only get, only set, or both get and set accessors.

Be careful with index bounds to avoid runtime errors.

Summary

Multi-parameter indexers let you use more than one key to access data.

They make classes behave like multi-dimensional arrays or tables.

Use them to simplify code that needs multiple keys to find values.