CSharp-Coder

Last updated: October 22, 2026 · Tested with .NET 11 RC2 (SDK 11.0.100-rc.2.26504.105, C# 15) and the .NET 10.0.12 runtime Short answer: C# 15 adds union types . You declare one with the union keyword and a list of case types. Any value of a case type converts to the union implicitly, and a switch expression over the union is checked for exhaustiveness: no _ => arm needed, and you get a warning if you forget a case. public record class Cat(string Name); public record class Dog(string Name); public record class Bird(string Name); public union Pet(Cat, Dog, Bird); // 1. Basics: implicit conversion and an exhaustive switch Pet pet = new Dog("Rex"); Console.WriteLine($"1. {Describe(pet)}"); static string Describe(Pet pet) => pet switch { Dog d => $"dog {d.Name}", Cat c => $"cat {c.Name}", Bird b => $"bird {b.Name}", }; That's the feature most C# developers have asked for under the name "disc...

Last updated: October 19, 2026 · Tested with Moq 4.21.0 and 4.20.72, xUnit 2.9.3, .NET 10 (SDK 10.0.401, runtime 10.0.12), Windows 11 Short answer: Create a mock with new Mock<IMyService>() , tell it what to return with Setup(...).Returns(...) (or ReturnsAsync for async methods), pass mock.Object into the class you test, and check the calls afterwards with Verify(..., Times.Once) . Below is a complete xUnit test suite I ran on Moq 4.21.0, the first Moq release in two years (September 24, 2026), plus the exact exception text for the ten mistakes people hit most. Things I found while testing: Upgrading to Moq 4.21.0 added a compiler warning (CS8602) to the usual ILogger verify code. With warnings as errors, the build fails. On 4.20.72 the same code had 0 warnings. You can't set up or verify logger.LogInformation(...) . It's an extension method, so you verify Log(...) instead. An async method you didn't set up doesn't return null . It returns a completed...

Last updated: October 18, 2026 · Tested with .NET 10 (SDK 10.0.401, ASP.NET Core 10.0.12), compared with ASP.NET Core 9.0.14, Windows 11 Short answer: Implement IExceptionHandler , register it with builder.Services.AddExceptionHandler<T>() , add builder.Services.AddProblemDetails() and call app.UseExceptionHandler() . Handlers run in registration order until one returns true , so put the catch-all last. I built three handlers (validation → 400, not found → 404, everything else → 500) on .NET 10 and tested them with curl. Four results you should know before you ship: Registering the global handler first turned every 404 into a 500. Browser requests ( Accept: text/html ) got an empty 500 until I added a fallback. The developer exception page never showed. .NET 10 stopped logging exceptions your handler handles ; .NET 9 logged them.

Last updated: October 8, 2026 · Tested with .NET 10 (SDK 10.0.401, runtime 10.0.12), Newtonsoft.Json 13.0.4, BenchmarkDotNet 0.15.8, Windows 11 Short answer: on .NET 10, use System.Text.Json for new code and for most migrations. It ships with the runtime, it is what ASP.NET Core uses by default, and in my benchmark it serialized a 20-line order about twice as fast as Newtonsoft.Json with a quarter of the allocations. Keep Newtonsoft.Json where you depend on its leniency: input with comments or non-ISO dates you can't change, JObject / dynamic -heavy code, existing TypeNameHandling payloads, or dictionaries keyed by custom types. Most migration bugs come from different defaults, not missing features. Below is every difference I hit, with the exact exception messages from real runs.

Last updated: October 8, 2026 · Tested with .NET 10 (SDK 10.0.401, runtime 10.0.12), Microsoft.Extensions.Http.Resilience 10.10.0 (Polly.Core 8.4.2), Windows 11 Short answer: don't create a new HttpClient() per request. Get clients from IHttpClientFactory ( AddHttpClient , named or typed), or keep one static HttpClient on a long-lived SocketsHttpHandler with PooledConnectionLifetime set so DNS changes are picked up. For retries and timeouts add AddStandardResilienceHandler() from Microsoft.Extensions.Http.Resilience and let it own the timeouts. Below is what I measured against a local Kestrel test server: 2,000 sockets left in TIME_WAIT by the per-request pattern, the exact timeout exceptions, real retry logs, a measured Retry-After delay, and one surprise: the standard handler silently replaces your HttpClient.Timeout .

Last updated: October 5, 2026 · Tested with CSharpier 1.3.0 (dotnet tool and CSharpier.MSBuild), dotnet format from SDK 10.0.401, Windows 11 Short answer: CSharpier is an opinionated formatter: it rewraps long lines, sorts usings and gives every file the same layout, with almost nothing to configure. dotnet format ships with the SDK and fixes spacing, indentation and code-style rules from .editorconfig , but it never wraps a long line. Use CSharpier for layout and keep dotnet format style and analyzers for code rules. Don't run dotnet format whitespace on top of CSharpier: with a common .editorconfig setting the two tools undo each other and your CI check fails either way. Below are the real before/after files, timings on 3,050 files, and the setup that worked.

Last updated: October 5, 2026 · Tested with .NET 10 (SDK 10.0.401, runtime 10.0.12), Microsoft.CodeAnalysis.CSharp 5.9.0, System.CodeDom 10.0.12, Windows 11 Short answer: CSharpCodeProvider cannot compile code on .NET Core or .NET 5+. Without the System.CodeDom package the code doesn't build (CS1069), and with it, CompileAssemblyFromSource throws PlatformNotSupportedException at runtime. The replacement is Roslyn: add Microsoft.CodeAnalysis.CSharp , build a CSharpCompilation , Emit it to a MemoryStream and load the bytes. Below is the working version on .NET 10, plus the four things that broke when I tried it: the reference list from most older examples fails with CS0012, compiled assemblies never unload unless you use a collectible AssemblyLoadContext , single-file publishing breaks references, and a CancellationToken does not stop code that never returns.

Learn C# for Unity from beginner to advanced in 2026 — MonoBehaviour lifecycle, coroutines, async, performance and DOTS. Start building games today. If you want to build games in 2026, learning C# for Unity is still the single highest-leverage skill you can pick up. Unity ships with C# as its only first-class scripting language, and the version of C# you write inside the editor today is a modern, fast, fully-featured language — not the cut-down dialect people remember from a decade ago. This guide walks you from your very first MonoBehaviour to advanced topics like the Job System, object pooling and allocation-free game loops, with runnable code you can paste straight into a project. Why C# for Unity Is Different From "Normal" C# Everything you know about .NET still applies — LINQ, generics, async , pattern matching, records. But Unity adds a layer on top that trips up almost every newcomer, and understanding it early will save you weeks. You don't own the ...

Learn API security best practices for 2026 with runnable C# and ASP.NET Core examples — JWT, rate limiting, BOLA fixes. Start hardening your REST API today. If you ship a REST API in 2026, you are running a public attack surface. Attackers no longer bother with your UI — they read your OpenAPI document, enumerate your endpoints, and hammer them directly. This guide covers the API security best practices that actually matter today, with runnable C# and ASP.NET Core examples you can drop into a real project. We will focus on the failures that show up in genuine breach reports: broken object-level authorization, weak token validation, missing rate limits, and secrets sitting in source control. Every example targets ASP.NET Core on .NET 8 or later, and each one explains why the control exists — because a security rule you do not understand is a security rule you will disable the first time it breaks a deployment. Why REST API Security Fails: The OWASP API Security Top 10 The OW...

Learn Serilog structured logging in .NET with runnable C# examples, sinks, enrichers, and production best practices. Start logging smarter today. If you have ever opened a 400 MB text log file at 2 a.m. trying to figure out why one customer's checkout failed, you already understand why Serilog .NET exists. Traditional logging writes sentences. Serilog writes data. That single difference — structured logging instead of string concatenation — is what turns your logs from a wall of text into a queryable database of everything your application did in production. In this tutorial you will learn how to set up Serilog in a .NET 8/9 application, configure sinks and enrichers, use scopes and correlation IDs, and apply the production best practices that separate a hobby project from a system you can actually operate. Every example is runnable. What Is Structured Logging (and Why String Logs Fail) Consider the classic approach: // The old way — information is destroyed at write ti...