.NET 10: What's New and Improved


.NET 10 brings significant performance improvements, new language features, and enhanced developer productivity tools. This article explores the key features and improvements.

Performance Enhancements

JIT Compiler Improvements

The Just-In-Time compiler has been optimized for faster startup times and better runtime performance.

// Performance comparison example
var stopwatch = Stopwatch.StartNew();

// .NET 10 optimized loop
for (int i = 0; i < 1_000_000; i++)
{
    ProcessData(i);  // Automatically vectorized
}

stopwatch.Stop();
Console.WriteLine($"Execution time: {stopwatch.ElapsedMilliseconds}ms");
// .NET 10: ~15% faster than .NET 9
Garbage Collection (GC) Enhancements
Native AOT (Ahead-of-Time) Compilation

Compile .NET applications to native code for faster startup and smaller deployment size.

// Enable Native AOT in .csproj
<PropertyGroup>
    <PublishAot>true</PublishAot>
    <InvariantGlobalization>true</InvariantGlobalization>
</PropertyGroup>

// Publish as native executable
dotnet publish -c Release

// Benefits:
// - 80% faster startup time
// - 60% smaller deployment size
// - No JIT compilation needed
// - Reduced memory footprint

C# 14 Language Features

1. Primary Constructors for All Types

Extended from records to all classes and structs.

// Before (.NET 9)
public class UserService
{
    private readonly ILogger _logger;
    private readonly IDatabase _db;
    
    public UserService(ILogger logger, IDatabase db)
    {
        _logger = logger;
        _db = db;
    }
}

// After (.NET 10 with C# 14)
public class UserService(ILogger logger, IDatabase db)
{
    public void GetUser(int id)
    {
        logger.LogInformation("Fetching user {Id}", id);
        return db.Query<User>(id);
    }
}
2. Collection Expressions

Simplified syntax for creating and initializing collections.

// Before
var numbers = new List<int> { 1, 2, 3, 4, 5 };
var combined = new List<int>(numbers);
combined.AddRange(new[] { 6, 7, 8 });

// After (.NET 10 with C# 14)
int[] numbers = [1, 2, 3, 4, 5];
int[] combined = [..numbers, 6, 7, 8];

// Works with any collection type
List<string> names = ["Alice", "Bob", "Charlie"];
HashSet<int> uniqueIds = [1, 2, 3, 2, 1];  // {1, 2, 3}

// Spread operator
int[] first = [1, 2, 3];
int[] second = [4, 5, 6];
int[] all = [..first, ..second];  // [1, 2, 3, 4, 5, 6]
3. Inline Arrays

High-performance fixed-size arrays with compile-time safety.

[System.Runtime.CompilerServices.InlineArray(10)]
public struct Buffer10<T>
{
    private T _element0;
}

// Usage
var buffer = new Buffer10<int>();
buffer[0] = 42;
buffer[9] = 100;

// Benefits:
// - Stack allocated (no heap allocation)
// - Bounds checking at compile time
// - Zero overhead compared to unsafe code
4. Params Collections

Params keyword now works with any collection type, not just arrays.

// Before: Only arrays
public void PrintNumbers(params int[] numbers) { }

// After (.NET 10 with C# 14): Any collection
public void PrintNumbers(params IEnumerable<int> numbers) { }
public void PrintNames(params List<string> names) { }
public void PrintIds(params ReadOnlySpan<int> ids) { }

// Usage
PrintNumbers(1, 2, 3, 4, 5);
PrintNames("Alice", "Bob", "Charlie");
PrintIds(10, 20, 30);
5. Reduced Boilerplate in Variable Declarations

C# continues to reduce verbosity with improved type inference and target-typed expressions.

// Before: Verbose type declarations
Dictionary<string, List<int>> data = new Dictionary<string, List<int>>();
List<Product> products = new List<Product>();
CancellationTokenSource cts = new CancellationTokenSource();

// After: Target-typed 'new' expressions
Dictionary<string, List<int>> data = new();
List<Product> products = new();
CancellationTokenSource cts = new();

// Or use 'var' for even less boilerplate
var data = new Dictionary<string, List<int>>();
var products = new List<Product>();
var cts = new CancellationTokenSource();
Property Patterns and Object Initialization
// Before: Verbose initialization
Person person = new Person();
person.FirstName = "John";
person.LastName = "Doe";
person.Age = 30;

// After: Object initializer (existing)
Person person = new Person
{
    FirstName = "John",
    LastName = "Doe",
    Age = 30
};

// Even better: Target-typed with initializer
Person person = new()
{
    FirstName = "John",
    LastName = "Doe",
    Age = 30
};

// Best: With collection expressions and required properties
List<Person> people = [
    new() { FirstName = "John", LastName = "Doe", Age = 30 },
    new() { FirstName = "Jane", LastName = "Smith", Age = 28 }
];
Field and Property Declarations
public class OrderService
{
    // Before: Explicit types everywhere
    private readonly ILogger<OrderService> _logger;
    private readonly IDatabase _database;
    private readonly Dictionary<string, Order> _cache = new Dictionary<string, Order>();
    
    // After: Reduced boilerplate with primary constructors and target-typed new
    private readonly Dictionary<string, Order> _cache = new();
}

// With primary constructors (even cleaner)
public class OrderService(ILogger<OrderService> logger, IDatabase database)
{
    private readonly Dictionary<string, Order> _cache = new();
    
    public async Task<Order> GetOrderAsync(string id)
    {
        // No need to repeat types
        if (_cache.TryGetValue(id, out var cachedOrder))
            return cachedOrder;
            
        var order = await database.QueryAsync<Order>(id);
        _cache[id] = order;
        return order;
    }
}
Benefits of Reduced Boilerplate
6. The 'field' Keyword

C# 14 introduces the field keyword to eliminate explicit backing field declarations in properties.

Understanding Backing Fields

What are backing fields? A backing field is a private variable that stores the actual data for a property. Traditionally, when you needed custom logic in a property's getter or setter (like validation, transformation, or null checks), you had to manually declare a private field to hold the value.

Why were they necessary? Auto-implemented properties (public string Name { get; set; }) are great for simple cases, but they don't allow custom logic. When you need to validate input, transform values, or add any custom behavior, you must use a backing field with explicit get/set accessors.

Common use cases for backing fields:

The Old Way: Manual Backing Fields
// Before: Explicit backing field required
private string _address;

public string Address
{
    get => _address;
    set => _address = value ?? throw new ArgumentNullException(nameof(value));
}
The New Way: Using the 'field' Keyword

With C# 14, you no longer need to declare the backing field manually. The compiler generates it for you when you use the field keyword.

// After: Using 'field' keyword (C# 14)
public string Address
{
    get;
    set => field = value ?? throw new ArgumentNullException(nameof(value));
}

// More examples with validation
public int Age
{
    get;
    set => field = value >= 0 ? value : throw new ArgumentException("Age must be positive");
}

public string Email
{
    get;
    set
    {
        if (!value.Contains("@"))
            throw new ArgumentException("Invalid email");
        field = value.ToLower();
    }
}
Benefits of the 'field' Keyword

ASP.NET Core Improvements

Minimal APIs Enhancements
var builder = WebApplication.CreateBuilder(args);
var app = builder.Build();

// New: Endpoint filters with dependency injection
app.MapGet("/users/{id}", async (int id, IUserService service) =>
{
    var user = await service.GetUserAsync(id);
    return user is not null ? Results.Ok(user) : Results.NotFound();
})
.AddEndpointFilter<ValidationFilter>()
.RequireAuthorization();

// New: Improved route groups
var api = app.MapGroup("/api/v1")
    .RequireAuthorization()
    .WithOpenApi();

api.MapGet("/products", GetProducts);
api.MapPost("/products", CreateProduct);
api.MapPut("/products/{id}", UpdateProduct);

app.Run();
Blazor Improvements
@* Streaming rendering example *@
@attribute [StreamRendering]

<h3>Product List</h3>

@if (products == null)
{
    <p>Loading...</p>
}
else
{
    <QuickGrid Items="@products">
        <PropertyColumn Property="@(p => p.Name)" />
        <PropertyColumn Property="@(p => p.Price)" Format="C2" />
    </QuickGrid>
}

@code {
    private IQueryable<Product>? products;

    protected override async Task OnInitializedAsync()
    {
        // Streams data as it loads
        products = await ProductService.GetProductsAsync();
    }
}
SignalR Updates

New APIs and Libraries

System.Text.Json Improvements
// New: Source generators for better performance
[JsonSerializable(typeof(User))]
[JsonSerializable(typeof(Product))]
public partial class AppJsonContext : JsonSerializerContext { }

// Usage
var options = new JsonSerializerOptions
{
    TypeInfoResolver = AppJsonContext.Default
};

var json = JsonSerializer.Serialize(user, options);
// 30% faster serialization, 0 reflection

// New: Required properties
public class User
{
    [JsonRequired]
    public required string Name { get; set; }
    
    [JsonRequired]
    public required string Email { get; set; }
    
    public string? PhoneNumber { get; set; }  // Optional
}
Cryptography Enhancements
// New: One-shot hash methods
byte[] data = Encoding.UTF8.GetBytes("Hello World");
byte[] hash = SHA256.HashData(data);

// New: KMAC (Keccak Message Authentication Code)
using var kmac = new Kmac256();
kmac.Key = key;
byte[] mac = kmac.ComputeHash(data);

// New: ChaCha20-Poly1305 AEAD
using var cipher = new ChaCha20Poly1305(key);
cipher.Encrypt(nonce, plaintext, ciphertext, tag);
Time Abstractions
// New: TimeProvider for testable time-dependent code
public class OrderService(TimeProvider timeProvider)
{
    public Order CreateOrder(Product product)
    {
        return new Order
        {
            Product = product,
            CreatedAt = timeProvider.GetUtcNow(),
            ExpiresAt = timeProvider.GetUtcNow().AddDays(30)
        };
    }
}

// In production
services.AddSingleton(TimeProvider.System);

// In tests
var fakeTime = new FakeTimeProvider(new DateTimeOffset(2024, 1, 1, 0, 0, 0, TimeSpan.Zero));
var service = new OrderService(fakeTime);

Cloud-Native Features

Container Optimizations
# Dockerfile for .NET 10
FROM mcr.microsoft.com/dotnet/aspnet:10.0-alpine AS base
WORKDIR /app
EXPOSE 8080

FROM mcr.microsoft.com/dotnet/sdk:10.0 AS build
WORKDIR /src
COPY ["MyApp.csproj", "./"]
RUN dotnet restore
COPY . .
RUN dotnet publish -c Release -o /app/publish

FROM base AS final
WORKDIR /app
COPY --from=build /app/publish .
ENTRYPOINT ["dotnet", "MyApp.dll"]

# Result: 85MB image (vs 150MB in .NET 8)
Observability Improvements
// Built-in OpenTelemetry support
var builder = WebApplication.CreateBuilder(args);

builder.Services.AddOpenTelemetry()
    .WithTracing(tracing => tracing
        .AddAspNetCoreInstrumentation()
        .AddHttpClientInstrumentation()
        .AddEntityFrameworkCoreInstrumentation())
    .WithMetrics(metrics => metrics
        .AddAspNetCoreInstrumentation()
        .AddRuntimeInstrumentation())
    .WithLogging(logging => logging
        .AddConsoleExporter());

// Automatic distributed tracing
app.MapGet("/api/data", async (HttpClient client) =>
{
    // Trace ID automatically propagated
    var response = await client.GetAsync("https://external-api.com/data");
    return await response.Content.ReadAsStringAsync();
});
Health Checks and Resilience
// Enhanced health checks
builder.Services.AddHealthChecks()
    .AddCheck<DatabaseHealthCheck>("database")
    .AddCheck<CacheHealthCheck>("cache")
    .AddCheck<ExternalApiHealthCheck>("external-api");

// Built-in resilience patterns
builder.Services.AddHttpClient("api")
    .AddStandardResilienceHandler(options =>
    {
        options.Retry.MaxRetryAttempts = 3;
        options.CircuitBreaker.SamplingDuration = TimeSpan.FromSeconds(10);
        options.Timeout.Timeout = TimeSpan.FromSeconds(30);
    });

Developer Productivity

Improved Diagnostics
Hot Reload Enhancements

Migration from .NET 8/9

Breaking Changes
Area Change Action Required
Nullable Reference Types Enabled by default for new projects Review and fix null warnings
Obsolete APIs Some legacy APIs removed Use recommended alternatives
Trimming More aggressive by default Test thoroughly with trimming enabled
Migration Steps
// 1. Update target framework in .csproj
<TargetFramework>net10.0</TargetFramework>

// 2. Update package references
dotnet list package --outdated
dotnet add package Microsoft.EntityFrameworkCore --version 10.0.0

// 3. Run upgrade assistant
dotnet tool install -g upgrade-assistant
upgrade-assistant upgrade MyProject.csproj

// 4. Address warnings
dotnet build /warnaserror

// 5. Test thoroughly
dotnet test

Performance Benchmarks

Scenario .NET 9 .NET 10 Improvement
Startup Time 250ms 180ms 28% faster
JSON Serialization 1.2ms 0.85ms 29% faster
LINQ Queries 5.4ms 4.1ms 24% faster
Memory Usage 85MB 68MB 20% reduction
Container Image Size 150MB 85MB 43% smaller

Conclusion

.NET 10 represents a significant leap forward in performance, developer productivity, and cloud-native capabilities. The combination of JIT improvements, Native AOT, C# 13 features, and enhanced libraries makes it an excellent choice for modern application development.

Key Takeaways