C# Tutorials: Language Features, Patterns and Performance

Last updated: October 5, 2026

Every C# language article on this site in one place: what changed in recent versions, the core features you use daily, writing fast code, design patterns, testing, and writing secure code. Posts marked tested on .NET 10 were rewritten from a working project, with real compiler errors, output and measurements.

Hit one of these? Start here

You see this	Read this
CS0131 on new int[5] { [^1] = 1 }, or not sure which C# 13/14 feature needs which .NET version	C# 13 and C# 14 features
params ReadOnlySpan<T> and an existing array picking different overloads	C# 13: params collections, measured
CS0150 when the column width in {value,width} is a variable	String interpolation and alignment
Two SaveChanges calls and half the data written after a failure	Repository and Unit of Work with EF Core
Visual Studio suggests IDE0290 Use primary constructor and you are not sure it is safe	Primary constructors explained

1. What's new in C#

• C# 13 and C# 14 features: params collections with measured allocations, the new Lock type benchmarked, partial properties, the field keyword and what C# 14 added on .NET 10. (rewritten and tested on .NET 10)
• Primary constructors: how the parameters are captured, classes vs records, and the pitfalls before you accept IDE0290 everywhere.
• Pattern matching: type, property and list patterns, switch expressions and when guards.
• Nullable reference types: enabling them, reading the warnings, the nullable attributes and migrating an existing codebase.
• Records vs classes vs structs: value vs reference semantics and a decision cheat sheet.
• Extension methods: writing them well, real examples, and extension members in C# 14.

2. Core language

• Generics: generic classes and methods, constraints and real-world uses.
• Delegates, events, Func and Action: from a delegate type to events with EventHandler<T>, and the closure trap in loops.
• Interface vs abstract class: the real differences, default interface methods and when to pick each.
• Async/await: how it works underneath, concurrent calls, and the common mistakes.
• Exception handling: custom exceptions, logging them properly, and exceptions vs the Result pattern.
• LINQ: Where, Select, OrderBy, GroupBy and aggregates on everyday data.
• Access modifiers: public, private, protected, internal and protected internal in one short reference.

3. Strings, collections and performance

Measure before you optimise; the profiling guide shows how.

• String interpolation and StringBuilder: interpolation, alignment and padding, and when concatenation becomes a performance problem. (rewritten and tested on .NET 10)
• List vs Dictionary vs HashSet: Big-O cheat sheet, a benchmark and a quick decision guide.
• Frozen collections: FrozenDictionary and FrozenSet vs immutable and read-only collections.
• Span&lt;T&gt; and Memory&lt;T&gt;: zero-allocation code and measuring it with BenchmarkDotNet.
• Source generators: the compilation pipeline, a first generator, debugging and testing it.
• Profiling with dotTrace and PerfView: finding the real bottleneck in a slow program before changing code.

4. Design and architecture

• SOLID principles: each principle with a C# example, plus interview-style quick answers.
• Design patterns: factory, singleton, observer and strategy, and how to choose.
• Dependency injection: constructor injection, scoped vs transient vs singleton, and keyed services.
• Repository pattern: basic and generic repositories, DI registration and testing.
• Repository and Unit of Work with EF Core: seven runs against a real database showing what one SaveChanges does and does not protect. (rewritten and tested on .NET 10)
• Domain-driven design: entities, value objects, aggregates and domain events.
• Event-driven architecture: from C# events to MediatR domain events to integration events between services.

5. Testing and team practice

• TDD with xUnit and Moq: red-green-refactor on an order service and isolating dependencies with Moq.
• Code review checklist: what to look for in a C# pull request and a one-page checklist.
• Git for .NET teams: trunk-based branching, commits and pull requests that stay reviewable.

6. Writing secure C#

• SQL injection prevention: parameterised ADO.NET, EF Core raw SQL done safely and stored procedures.
• Hash passwords: PBKDF2, ASP.NET Core Identity's PasswordHasher and bcrypt, and why SHA-256 is the wrong tool.
• Encryption: AES, RSA and hashing: symmetric vs asymmetric encryption and hashing for integrity.

7. C# beyond the backend

• .NET MAUI: a first cross-platform app with XAML, MVVM and API calls.
• C# for Unity: how Unity C# differs, events and time, the fake-null trap and performance.

Related guides

Building web APIs with these features? The ASP.NET Core tutorials guide covers APIs, security, observability and deployment.