csharp-dotnet

C# & .NET

Overview

Modern C# and .NET development patterns including async programming, LINQ, and ASP.NET Core.

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Modern C# Features

Records and Init-Only Properties

// Record type (immutable by default)
public record User(
    string Id,
    string Email,
    string Name,
    DateTime CreatedAt
);

// With-expressions for immutable updates
var user = new User("1", "[email protected]", "Test User", DateTime.UtcNow);
var updated = user with { Name = "Updated Name" };

// Record with validation
public record ValidatedUser
{
    public required string Id { get; init; }
    public required string Email { get; init; }
    public required string Name { get; init; }

    public ValidatedUser()
    {
        // Validation in constructor
    }

    // Custom validation
    public static ValidatedUser Create(string email, string name)
    {
        if (!email.Contains("@"))
            throw new ArgumentException("Invalid email");

        return new ValidatedUser
        {
            Id = Guid.NewGuid().ToString(),
            Email = email,
            Name = name
        };
    }
}

// Init-only properties
public class Config
{
    public required string ConnectionString { get; init; }
    public int Timeout { get; init; } = 30;
}

Pattern Matching

// Type patterns
public string Describe(object obj) => obj switch
{
    string s => $"String of length {s.Length}",
    int i when i > 0 => $"Positive integer: {i}",
    int i => $"Non-positive integer: {i}",
    IEnumerable<int> list => $"Integer list with {list.Count()} items",
    null => "Null value",
    _ => "Unknown type"
};

// Property patterns
public decimal CalculateDiscount(Order order) => order switch
{
    { Total: > 1000, Customer.IsPremium: true } => order.Total * 0.2m,
    { Total: > 1000 } => order.Total * 0.1m,
    { Customer.IsPremium: true } => order.Total * 0.05m,
    _ => 0
};

// List patterns (C# 11)
public string DescribeList(int[] numbers) => numbers switch
{
    [] => "Empty",
    [var single] => $"Single element: {single}",
    [var first, var second] => $"Two elements: {first}, {second}",
    [var first, .. var middle, var last] => $"First: {first}, Last: {last}, Middle count: {middle.Length}",
};

// Positional patterns with deconstruct
public record Point(int X, int Y);

public string Quadrant(Point point) => point switch
{
    (0, 0) => "Origin",
    (> 0, > 0) => "First quadrant",
    (< 0, > 0) => "Second quadrant",
    (< 0, < 0) => "Third quadrant",
    (> 0, < 0) => "Fourth quadrant",
    (_, 0) or (0, _) => "On an axis"
};