C# 8 in Libraries and Applications

C# 8 in Libraries and Applications

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  C# 8 inLibraries and Applications Christian Nagel https://csharp.christiannagel.com
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  Topics NEW C# 8FEATURES HOW TO USE C# 8 IN LIBRARIES AND APPLICATIONS GUIDELINES
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  Christian Nagel • Training •Coaching • Consulting • Development • Microsoft MVP • www.cninnovation.com • csharp.christiannagel.com • github.com/cninnovation
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  How to useC# 8
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  How to useC# 8 • By default enabled with .NET Core 3.0 • Enable with other projects • <LangVersion>8.0</LangVersion> • <Nullable>enable</Nullable> • Directory.Build.Props
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  Features based on Frameworks/Runtimes •Syntax Sugar Features mit allen Frameworks • Manche Features brauchen Klassen & Interfaces • Ranges, async streams • Runtime Updates Required • .NET Standard 2.1 • Default Interface Members
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  Default Interface Members
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  Default Interface Members - Overview • Interfacesmit Implementierung • Modifiers: private, protected, internal, public, virtual, abstract, override, sealed, static, extern
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  Default Interface Methods Ändernvon Interfaces ohne Breaking Changes 1 Traits – Wiederverwendbarkeit von Methoden in unabhängigen Klassen 2 Basiert auf Java's Default Methods 3
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  Default Interface Methods •Changing the interface without breaking changes public interface ILogger { void Log(string message); } public interface Ilogger { void Log(string message); void Log(Exception ex) => Log(ex.Message); } public class MyLogger : ILogger { public void Log(string message) => Console.WriteLine(message); }
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  Demo • Default InterfaceMembers • Interface mit breaking change • Interface mit non-breaking change • Traits
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  Tipps Ist die ersteVersion eines Interfaces komplett? Erweiterungen sind jetzt möglich! Alternative zu Extension Methoden Runtime-Erweiterungen!
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  Indices and Ranges
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  Indexes and Ranges Indexund Range & Types & Extensions New Operators • ^ Hat Operator • .. Range Operator
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  Hat Operator int[] arr= { 1, 2, 3 }; int lastItem = arr[^1];
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  Range string text1 ="the quick brown fox jumped over the lazy dogs"; string quick = text1[4..9]; string dog = text1[^4..^1]; string brownfoxjumpedandmore = text1[10..]; string thequick = text1[..8]; string text2 = text1[..];
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  Demo • Ranges andIndices • Access Slice of Span<T> • Access String • Range, Index Types • Custom Collections
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  Implicit Support Index •countable (Length, Count) •instanceindexer with int Range •countable •Slice method with two int
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  Nullable Reference Types
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  Null References Most common.NET Exception NullReferenceException Billion Dollar Mistake 1965 in Algol by Tony Hoare "Billion Dollar Mistake"
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  Null Conditional Operator(C# 6) • Null checks made easier int? length = customers?.Length; Customer first = customers?[0]; int? count = customers?[0]?.Orders?.Count(); public void OnPropertyChanged([CallerMemberName] string propertyName = null) => PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
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  Coalescing Operator (C#5) • Default values for null int length = customers?.Length ?? 0; public bool CanExecute(object parameter) => _canExecute?.Invoke() ?? true;
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  Reference Types are not Nullable •#nullable enable/disable/restore • annotated with ? – nullable reference type • string? • Null-forgiving operator • ! • Null-coalescing assignment • numbers ??= new List<string>();
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  Nullable Reference Types •Dokumentation: null oder nicht null • Hilft finden von Bugs, aber keine Garantie! • Flow analysis - tracks nullable reference variables • Breaks existing code (opt-in) • Nullability implemented with metadata (ignored by downlevel compilers) • string, T non-nullable • string?, T? nullable
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  Demo • Nullable ReferenceTypes • Enable nullability • Add annotations • Solving issues • Current issues
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  Guidelines • Library authors– Nullable adoption phase before .NET 5 • App developers – nullability on your own pace • Annotate new APIs • Do not remove argument validation • Parameter is non-nullable if parameters are checked (ArgumentNullException) • Parameter is nullable if documented to accept null • Prefer nullable over non-nullable with disagreements
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  Async Streams
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  Async Streams bis jetzt: async/awaitliefert ein Ergebnis Async Streams erweitert async/await mit Stream von Ergebnissen Asynchronous Datenquellen die vom Consumer kontrolliert werden Alternative zu System.Reactive
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  Async Streams • IAsyncDisposable •IAsyncEnumerable • IAsyncEnumerator public interface IAsyncDisposable { ValueTask DisposeAsync(); } public interface IAsyncEnumerable<out T> { IAsyncEnumerator<T> GetAsyncEnumerator(); } public interface IAsyncEnumerator<out T> : IAsyncDisposable { ValueTask<bool> MoveNextAsync(); T Current { get; } }
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  Using Async Streams •await foreach IAsyncEnumerator<T> enumerator = enumerable.GetAsyncEnumerator(); try { while (await enumerator.MoveNextAsync()) { Use(enumerator.Current); } } finally { await enumerator.DisposeAsync(); } await foreach (var i in enumerable) { Use(i); }
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  Async with yield •return IAsyncEnumerable static async IAsyncEnumerable<int> MyIterator() { try { for (int i = 0; i < 100; i++) { await Task.Delay(1000); yield return i; } } finally { await Task.Delay(200); Console.WriteLine("finally"); } }
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  Demo • Async Streams& SignalR • Streaming from the Server to the Client • Streaming from the Client to the Server • C# 8 Async Streams
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  More Features…
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  using declaration public voidMethod(IEnumerable<string> lines) { using var file = new StreamWriter("sample.txt"); foreach (var line in lines) { file.WriteLine(line); } }
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  switch Expression static stringM2(Shape shape) => shape switch { Shape s when s.Size.height > 100 => $"large shape with size {s.Size} at position {s.Position}", Ellipse e => $"Ellipse with size {e.Size} at position {e.Position}", Rectangle r => $"Rectangle with size {r.Size} at position {r.Position}", _ => "another shape" } };
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  Recursive, Property, andDiscard Patterns static string M3(Shape shape) => shape switch { CombinedShape (var shape1, var (pos, _)) => $"combined shape - shape1: {shape1.Name}, pos of shape2: {pos}", { Size: (200, 200), Position: var pos } => $"shape with size 200x200 at position {pos.x}:{pos.y}", Ellipse (var pos, var size) => $"Ellipse with size {size} at position {pos}", Rectangle (_, var size) => $"Rectangle with size {size}", _ => "another shape" };
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  Demo • Switch expressionswith tuples • Pattern matching
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  Summary Avoid Errors Better Productivity BetterPerformance
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  Questions?
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  For action • Annotatelibraries with nullability • Use new C# 8 features • https://csharp.christiannagel.com • https://github.com/cninnovation • https://github.com/ProfessionalCSharp
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  Thank you!