Pattern matching in switch in C Sharp (C#)

Introduction

Pattern matching in switch helps you check a value against different shapes or types easily. It makes your code cleaner and easier to read.

You want to run different code depending on the type of an object.

You want to check if a value fits a certain pattern or condition inside a switch.

You want to simplify complex if-else chains by using switch with patterns.

You want to extract parts of a value while checking its type.

You want to handle different cases clearly in one place.

Syntax

C Sharp (C#)

switch (variable)
{
    case TypeName variableName:
        // code when variable is TypeName
        break;
    case TypeName { Property: value } variableName:
        // code when variable matches pattern with property
        break;
    case int number when number > 0:
        // code when variable is int and greater than 0
        break;
    case null:
        // code when variable is null
        break;
    default:
        // code for all other cases
        break;
}

You can match types, properties, and add extra conditions with when.

Use default to catch all unmatched cases.

Examples

This checks the type of value and prints a message accordingly.

C Sharp (C#)

object value = 42;
switch (value)
{
    case int number:
        Console.WriteLine($"It's an integer: {number}");
        break;
    case string text:
        Console.WriteLine($"It's a string: {text}");
        break;
    default:
        Console.WriteLine("Unknown type");
        break;
}

This matches strings and checks if their length is greater than 3.

C Sharp (C#)

object value = "hello";
switch (value)
{
    case string { Length: > 3 } longText:
        Console.WriteLine($"Long string: {longText}");
        break;
    case string shortText:
        Console.WriteLine($"Short string: {shortText}");
        break;
    default:
        Console.WriteLine("Not a string");
        break;
}

This handles the case when the value is null.

C Sharp (C#)

object value = null;
switch (value)
{
    case null:
        Console.WriteLine("Value is null");
        break;
    default:
        Console.WriteLine("Value is not null");
        break;
}

Sample Program

This program shows how to use pattern matching in a switch to handle different types and conditions. It prints the items before and after applying the switch with patterns.

C Sharp (C#)

using System;

class Program
{
    static void Main()
    {
        object[] items = { 10, "hello", 3.14, null, "hi" };

        Console.WriteLine("Before switch pattern matching:");
        foreach (var item in items)
        {
            Console.WriteLine(item ?? "null");
        }

        Console.WriteLine("\nAfter switch pattern matching:");
        foreach (var item in items)
        {
            switch (item)
            {
                case int number when number > 5:
                    Console.WriteLine($"Integer greater than 5: {number}");
                    break;
                case int number:
                    Console.WriteLine($"Integer 5 or less: {number}");
                    break;
                case string { Length: > 3 } longText:
                    Console.WriteLine($"Long string: {longText}");
                    break;
                case string shortText:
                    Console.WriteLine($"Short string: {shortText}");
                    break;
                case null:
                    Console.WriteLine("Null value found");
                    break;
                default:
                    Console.WriteLine($"Other type: {item}");
                    break;
            }
        }
    }
}

Important Notes

Time complexity depends on the number of cases but is generally efficient for small sets.

Space complexity is minimal as no extra storage is needed beyond the switch.

Common mistake: forgetting to handle null values can cause runtime errors.

Use pattern matching in switch when you want clear, readable code for multiple type or condition checks instead of many if-else statements.

Summary

Pattern matching in switch lets you check types and conditions clearly.

You can match properties and add extra checks with when.

It helps write cleaner and easier-to-read code than many if-else statements.