Bits of .NET

Mutable objects causing threading issues? C# 9+ records provide immutable data structures with built-in value semantics.

Records vs Classes: When to Use Each

// Use RECORDS for:
// 1. Immutable data transfer objects (DTOs)
// 2. Value objects in domain-driven design
// 3. Configuration objects
// 4. API request/response models
// 5. Event objects in event sourcing

// Use CLASSES for:
// 1. Entities with identity and mutation
// 2. Services with behavior
// 3. Complex objects with inheritance hierarchies
// 4. Objects needing custom equality semantics
// 5. Framework base classes

// Example: Record for API response
public record ApiResponse(
    T Data,
    bool Success,
    string Message,
    DateTime Timestamp = default)
{
    public DateTime Timestamp { get; init; } = Timestamp == default 
        ? DateTime.UtcNow 
        : Timestamp;
}

// Usage:
var response = new ApiResponse(
    Data: product,
    Success: true,
    Message: "Product retrieved successfully");
    
// Immutable - cannot modify after creation
// Value equality - two responses with same data are equal
// Built-in ToString() with property values
// Deconstruction support

Advanced Record Patterns:

// Positional record (immutable by default)
public record Person(
    string FirstName,
    string LastName,
    int Age);

// With non-positional properties
public record Employee : Person
{
    public string EmployeeId { get; init; }
    public decimal Salary { get; init; }
    public Department Department { get; init; }
    
    public Employee(
        string firstName,
        string lastName,
        int age,
        string employeeId,
        decimal salary,
        Department department)
        : base(firstName, lastName, age)
    {
        EmployeeId = employeeId;
        Salary = salary;
        Department = department;
    }
}

// Record struct (C# 10+)
public readonly record struct Point(
    double X,
    double Y)
{
    public double DistanceFromOrigin => Math.Sqrt(X * X + Y * Y);
}

// With validation in init-only setters
public record OrderItem
{
    private int _quantity;
    private decimal _price;
    
    public int Quantity
    {
        get => _quantity;
        init
        {
            if (value <= 0)
                throw new ArgumentException("Quantity must be positive");
            _quantity = value;
        }
    }
    
    public decimal Price
    {
        get => _price;
        init
        {
            if (value < 0)
                throw new ArgumentException("Price cannot be negative");
            _price = value;
        }
    }
    
    public decimal Total => Quantity * Price;
}