Modern C# Features

C# evolves rapidly with annual releases. This lesson covers the most impactful features from recent versions (C# 9 through C# 12) that every modern C# developer should know.

---

Records (C# 9+)

Records are immutable reference types with built-in value equality:

// Record declaration
public record Person(string Name, int Age);

// Usage
var alice = new Person("Alice", 30);
var alice2 = new Person("Alice", 30);

Console.WriteLine(alice == alice2);     // True (value equality!)
Console.WriteLine(alice);              // Person { Name = Alice, Age = 30 }

// Non-destructive mutation with 'with'
var older = alice with { Age = 31 };
Console.WriteLine(older);  // Person { Name = Alice, Age = 31 }

Record Types

Type	Syntax	Value/Reference	Mutable
record (or record class)	record Person(string Name);	Reference	Immutable by default
record struct	record struct Point(int X, int Y);	Value	Mutable by default
readonly record struct	readonly record struct Point(int X, int Y);	Value	Immutable

Tip: Use records for data transfer objects (DTOs), domain models, and any type where value equality makes sense.

---