Recursive pattern matching in C Sharp (C#) - Mini Project: Build & Apply

Recursive Pattern Matching

📖 Scenario: Imagine you have a simple tree structure representing folders and files. Each folder can contain files or other folders. You want to find if a specific file exists anywhere inside this tree.

🎯 Goal: Build a C# program that uses recursive pattern matching to check if a file with a given name exists inside a nested folder structure.

📋 What You'll Learn

Create a record type File with a Name property.

Create a record type Folder with a Name property and a list of Items which can be File or Folder.

Write a recursive method ContainsFile that uses pattern matching to check if a file with a given name exists in the folder or any subfolder.

Print "Found" if the file exists, otherwise "Not Found".

💡 Why This Matters

🌍 Real World

File systems and many applications use nested folder structures. Searching files inside them is a common task.

💼 Career

Understanding recursive pattern matching helps in writing clean, readable code for complex data structures like trees, useful in software development and data processing jobs.

1

Create the data structure

Create a record called File with a string property Name, and a record called Folder with a string property Name and a list of objects called Items.

C Sharp (C#)

// Your code here

Need a hint?

Use C# 9+ record syntax to create simple data containers.

2

Create sample folder data

Create a variable root of type Folder representing a folder named "root" that contains a File named "readme.txt" and a subfolder named "docs" which contains a File named "manual.pdf".

C Sharp (C#)

public record File(string Name);
public record Folder(string Name, List Items);

// Your code here

Need a hint?

Use nested lists to represent folders inside folders.

3

Write the recursive pattern matching method

Write a method bool ContainsFile(Folder folder, string fileName) that uses a foreach loop and recursive pattern matching with switch expressions to check if any File with Name equal to fileName exists in folder or its subfolders.

C Sharp (C#)

public record File(string Name);
public record Folder(string Name, List Items);

var root = new Folder("root", new List
{
    new File("readme.txt"),
    new Folder("docs", new List
    {
        new File("manual.pdf")
    })
});

// Write the ContainsFile method below

Need a hint?

Use switch with pattern matching and recursion to check nested folders.

4

Print the search result

Write a Console.WriteLine statement that prints "Found" if ContainsFile(root, "manual.pdf") returns true, otherwise prints "Not Found".

C Sharp (C#)

public record File(string Name);
public record Folder(string Name, List Items);

var root = new Folder("root", new List
{
    new File("readme.txt"),
    new Folder("docs", new List
    {
        new File("manual.pdf")
    })
});

bool ContainsFile(Folder folder, string fileName)
{
    foreach (var item in folder.Items)
    {
        switch (item)
        {
            case File f when f.Name == fileName:
                return true;
            case Folder subFolder:
                if (ContainsFile(subFolder, fileName))
                    return true;
            break;
        }
    }
    return false;
}

// Print the result of searching for "manual.pdf" in root

Need a hint?

Use the ternary operator inside Console.WriteLine to print the result.