Bits of .NET

📦 Record Types = Immutable Data

Mutable data structures cause bugs. Record types provide immutable, value-based data with value semantics.

📝 Record Syntax

// Basic Record
public record User(string Name, int Age, string Email);

// Usage
var user = new User("John Doe", 30, "john@example.com");
var name = user.Name; // Read-only

// With Expression (Non-destructive mutation)
var updatedUser = user with { Age = 31 };

// Record with Methods
public record Product(string Name, decimal Price, string Category)
{
    public decimal WithDiscount(decimal discountPercent) 
        => Price - (Price * discountPercent / 100);

    public override string ToString() 
        => $"{Name} ({Category}) - ${Price}";
}

// Record Inheritance
public record Person(string Name, string Email);
public record Customer(string Name, string Email, string CustomerId) : Person(Name, Email);

🎯 Advanced Record Patterns

// Positional vs Nominal Records
// Positional (Primary Constructor)
public record Order(int Id, DateTime OrderDate, decimal Total);

// Nominal (Explicit Properties)
public record Customer
{
    public string FirstName { get; init; }
    public string LastName { get; init; }
    public string FullName => $"{FirstName} {LastName}";
}

// Record with Validation
public record ValidatedUser
{
    public string Name { get; init; }
    public int Age { get; init; }

    public ValidatedUser(string name, int age)
    {
        if (string.IsNullOrWhiteSpace(name))
            throw new ArgumentException("Name cannot be empty");
        if (age < 0 || age > 120)
            throw new ArgumentException("Invalid age");

        Name = name;
        Age = age;
    }
}

// Records in Collections
var users = new List<User>
{
    new User("Alice", 25, "alice@example.com"),
    new User("Bob", 30, "bob@example.com")
};

// Equality with Records
var user1 = new User("John", 30, "john@example.com");
var user2 = new User("John", 30, "john@example.com");

Console.WriteLine(user1 == user2); // True (Value equality)

// Records as DTOs
public record CreateUserRequest(string Name, string Email, int Age);
public record UpdateUserRequest(int Id, string Name, string Email);

💡 Record Best Practices

• Use records for immutable DTOs
• Use with expressions for updates
• Implement validation in constructors
• Use records for value-based data
• Prefer records over classes for data containers