Modern C# Features and Best Practices

# CHAPTER 30

Modern C# Features and Best Practices #

1. Introduction #

2. Learning Objectives #

• Use Top-Level Statements (C# 9).

• Understand and use record types for immutable data.

• Use advanced Pattern Matching.

• Understand Nullable Reference Types to prevent crashes.

• Apply Clean Code principles.

3. Top-Level Statements (C# 9.0) #

// The Old Way
using System;
namespace MyApp
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("Hello World!");
        }
    }
}

In modern C#, you can delete all of that. The compiler generates the namespace, class, and Main method for you automatically.

// The Modern Way (Top-Level Statements)
Console.WriteLine("Hello World!");

4. Records (C# 9.0) #

A record is a special class designed specifically for immutable data. It provides value-based equality out of the box (if two records have the same data, they are considered equal, unlike standard classes).

// Defines an entire immutable class in ONE line!
public record Employee(int Id, string Name);

// Usage
var emp1 = new Employee(1, "Alice");
var emp2 = new Employee(1, "Alice");

// In standard classes, this would be false. With records, it is true!
Console.WriteLine(emp1 == emp2); 

5. Advanced Pattern Matching (C# 8 & 9) #

int temp = 25;

// Property Pattern Matching
string weather = temp switch
{
    < 0 => "Freezing",
    >= 0 and < 15 => "Cold",
    >= 15 and <= 25 => "Perfect",
    > 25 => "Hot"
};

6. Nullable Reference Types (C# 8.0) #

Modern C# forces you to explicitly declare if a variable is allowed to be null using the ? operator.

// string name = null; // WARNING: Non-nullable string cannot be null!

string? optionalName = null; // OK! The ? marks it as explicitly nullable

// The compiler now FORCES you to check for null before using it:
if (optionalName != null)
{
    Console.WriteLine(optionalName.Length);
}

7. Clean Code Best Practices #

1. 1. Meaningful Names: Avoid variables like int d;. Use int daysUntilExpiry;.

1. 2. Single Responsibility Principle: A class or method should have only one reason to change. If your User class sends emails, validates passwords, and saves to the database, it is doing too much.

1. 3. Don't Repeat Yourself (DRY): If you copy and paste a block of code 3 times, extract it into a Method.

1. 4. Fail Fast: Validate data at the very beginning of your method and throw an exception immediately if it is invalid, rather than letting the code run and fail deep inside complex logic.

1. 5. Comment the 'Why', not the 'What':

8. Common Mistakes #

• Ignoring Compiler Warnings: Modern C# uses Nullable Reference Types to generate warnings, not errors. Many developers ignore them. If you treat warnings as errors, your applications will almost never crash in production.

9. Conclusion of the Course #

10. MCQs with Answers #

Q10. Is C# a stagnant language, or does it receive constant updates? a) It hasn't changed since 2005 b) It is aggressively updated by Microsoft, with new syntax and features added annually Answer: b) It is aggressively updated by Microsoft, with new syntax and features added annually

11. Interview Questions #

• Q: What is a record in C#, and when would you use it instead of a class?

• Q: Explain Nullable Reference Types and how they help prevent the "Billion Dollar Mistake".

12. Final Thoughts #