csharp-advanced-patterns

C# Advanced Patterns

Advanced C# language patterns and .NET 10 features for elegant, performant code.

When to Use

• Implementing complex business logic with pattern matching
• Optimizing async/await usage
• Writing performant code with Span/Memory
• Refactoring legacy code to modern C#
• Creating immutable DTOs with records

Modern C# Features (.NET 10)

Records for DTOs

// Immutable DTO with required properties
public record CreatePatientDto
{
    public required string FirstName { get; init; }
    public required string LastName { get; init; }
    public required string Email { get; init; }
    public DateTime DateOfBirth { get; init; }
}

// Positional record with deconstruction
public record PatientDto(Guid Id, string FullName, string Email);

// Usage
var (id, name, email) = patient;

Pattern Matching

// Switch expression for status handling
public string GetStatusMessage(AppointmentStatus status) => status switch
{
    AppointmentStatus.Scheduled => "Your appointment is confirmed",
    AppointmentStatus.Completed => "Thank you for visiting",
    AppointmentStatus.Cancelled => "Your appointment was cancelled",
    AppointmentStatus.NoShow => "You missed your appointment",
    _ => throw new ArgumentOutOfRangeException(nameof(status))
};

// Property pattern matching
public decimal CalculateDiscount(Patient patient) => patient switch
{
    { Age: > 65 } => 0.20m,
    { IsVeteran: true } => 0.15m,
    { Visits: > 10 } => 0.10m,
    _ => 0m
};

// List patterns (.NET 7+)
public string DescribeList(int[] numbers) => numbers switch
{
    [] => "Empty",
    [var single] => $"Single: {single}",
    [var first, .., var last] => $"First: {first}, Last: {last}",
};

Primary Constructors

// Class with primary constructor
public class PatientService(
    IRepository<Patient, Guid> repository,
    ILogger<PatientService> logger)
{
    public async Task<Patient> GetAsync(Guid id)
    {
        logger.LogInformation("Getting patient {Id}", id);
        return await repository.GetAsync(id);
    }
}