C# 9.0 Pocket Reference Instant Help for C# 9.0 Programmers Joseph Albahari & Ben Albahari C# 9.0 Pocket Reference Instant Help for C# 9.0 Programmers Joseph Albahari and Ben Albahari C# 9.0 Pocket Reference by Joseph Albahari and Ben Albahari Copyright © 2021 Joseph Albahari and Ben Albahari. All rights reserved. Printed in the United States of America. Published by O’Reilly Media, Inc., 1005 Gravenstein Highway North, Sebasto‐ pol, CA 95472. O’Reilly books may be purchased for educational, business, or sales promo‐ tional use. Online editions are also available for most titles (http://oreilly.com). For more information, contact our corporate/institutional sales department: 800-998-9938 or [email protected]. Acquisitions Editor: Amanda Quinn Development Editor: Corbin Collins Production Editor: Kristen Brown Copyeditor: Charles Roumeliotis Proofreader: James Fraleigh Indexer: WordCo Indexing Services, Inc. Interior Designer: David Futato Cover Designer: Karen Montgomery Illustrator: Kate Dullea January 2021: First Edition Revision History for the First Edition 2021-01-13: First Release See https://oreil.ly/c9pr_1 for release details. The O’Reilly logo is a registered trademark of O’Reilly Media, Inc. C# 9.0 Pocket Reference, the cover image, and related trade dress are trademarks of O’Reilly Media, Inc. The views expressed in this work are those of the authors, and do not repre‐ sent the publisher’s views. While the publisher and the authors have used good faith efforts to ensure that the information and instructions contained in this work are accurate, the publisher and the authors disclaim all responsi‐ bility for errors or omissions, including without limitation responsibility for damages resulting from the use of or reliance on this work. Use of the infor‐ mation and instructions contained in this work is at your own risk. If any code samples or other technology this work contains or describes is subject to open source licenses or the intellectual property rights of others, it is your responsibility to ensure that your use thereof complies with such licenses and/or rights. 978-1-098-10113-8 [LSI] Table of Contents C# 9.0 Pocket Reference 1 A First C# Program 2 Syntax 5 Type Basics 8 Numeric Types 19 Boolean Type and Operators 26 Strings and Characters 28 Arrays 32 Variables and Parameters 38 Expressions and Operators 47 Null Operators 53 Statements 55 Namespaces 65 Classes 69 Inheritance 87 The object Type 96 Structs 101 Access Modifiers 103 Interfaces 105 iii Enums 109 Nested Types 112 Generics 113 Delegates 122 Events 128 Lambda Expressions 134 Anonymous Methods 139 try Statements and Exceptions 140 Enumeration and Iterators 148 Nullable Value Types 154 Nullable Reference Types 158 Extension Methods 160 Anonymous Types 162 Tuples 163 Records (C# 9) 165 Patterns 172 LINQ 176 Dynamic Binding 202 Operator Overloading 210 Attributes 213 Caller Info Attributes 217 Asynchronous Functions 219 Unsafe Code and Pointers 230 Preprocessor Directives 235 XML Documentation 237 Index 241 iv | Table of Contents C# 9.0 Pocket Reference C# is a general-purpose, type-safe, primarily object-oriented programming language, the goal of which is programmer pro‐ ductivity. To this end, the language balances simplicity, expres‐ siveness, and performance. C# 9 is designed to work with the Microsoft .NET 5 runtime (whereas C# 8 targets .NET Core 3, and C# 7 targets .NET Core 2 and Microsoft .NET Framework 4.6/4.7/4.8). NOTE The programs and code snippets in this book mirror those in Chapters 2 through 4 of C# 9.0 in a Nutshell and are all available as interactive samples in LINQPad. Working through these samples in conjunction with the book accel‐ erates learning in that you can edit the samples and instantly see the results without needing to set up projects and solutions in Visual Studio. To download the samples, click the Samples tab in LINQ‐ Pad and then click “Download more samples.” LINQPad is free—go to www.linqpad.net. 1 A First C# Program Following is a program that multiplies 12 by 30 and prints the result, 360, to the screen. The double forward slash indicates that the remainder of a line is a comment: int x = 12 * 30; // Statement 1 System.Console.WriteLine (x); // Statement 2 Our program consists of two statements. Statements in C# exe‐ cute sequentially and are terminated by a semicolon. The first statement computes the expression 12 * 30 and stores the result in a variable, named x, whose type is a 32-bit integer (int). The second statement calls the WriteLine method on a class called Console, which is defined in a namespace called System. This prints the variable x to a text window on the screen. A method performs a function; a class groups function mem‐ bers and data members to form an object-oriented building block. The Console class groups members that handle command-line input/output (I/O) functionality, such as the WriteLine method. A class is a kind of type, which we examine in “Type Basics” on page 8. At the outermost level, types are organized into namespaces. Many commonly used types—including the Console class— reside in the System namespace. The .NET libraries are organ‐ ized into nested namespaces. For example, the System.Text namespace contains types for handling text, and System.IO contains types for input/output. Qualifying the Console class with the System namespace on every use adds clutter. The using directive lets you avoid this clutter by importing a namespace: using System; // Import the System namespace int x = 12 * 30; Console.WriteLine (x); // No need to specify System A basic form of code reuse is to write higher-level functions that call lower-level functions. We can refactor our program 2 | C# 9.0 Pocket Reference with a reusable method called FeetToInches that multiplies an integer by 12, as follows: using System; Console.WriteLine (FeetToInches (30)); // 360 Console.WriteLine (FeetToInches (100)); // 1200 int FeetToInches (int feet) { int inches = feet * 12; return inches; } Our method contains a series of statements surrounded by a pair of braces. This is called a statement block. A method can receive input data from the caller by specifying parameters and output data back to the caller by specifying a return type. Our FeetToInches method has a parameter for inputting feet, and a return type for outputting inches: int FeetToInches (int feet) ... The literals 30 and 100 are the arguments passed to the Feet ToInches method. If a method doesn’t receive input, use empty parentheses. If it doesn’t return anything, use the void keyword: using System; SayHello(); void SayHello() { Console.WriteLine ("Hello, world"); } Methods are one of several kinds of functions in C#. Another kind of function we used in our example program was the * operator, which performs multiplication. There are also con‐ structors, properties, events, indexers, and finalizers. A First C# Program | 3 Compilation The C# compiler compiles source code (a set of files with the .cs extension) into an assembly. An assembly is the unit of packag‐ ing and deployment in .NET. An assembly can be either an application or a library. A normal console or Windows applica‐ tion has an entry point, whereas a library does not. The purpose of a library is to be called upon (referenced) by an application or by other libraries. .NET 5 itself is a set of libraries (as well as a runtime environment). Each of the programs in the preceding section began directly with a series of statements (called top-level statements). The presence of top-level statements implicitly creates an entry point for a console or Windows application. (Without top-level statements, a Main method denotes an application’s entry point —see “Custom Type Examples” on page 9.) To invoke the compiler, you can either use an integrated devel‐ opment environment (IDE) such as Visual Studio or Visual Studio Code, or call it manually from the command line. To manually compile a console application with .NET, first down‐ load the .NET 5 SDK, and then create a new project, as follows: dotnet new console -o MyFirstProgram cd MyFirstProgram This creates a folder called MyFirstProgram, which contains a C# file called Program.cs, which you can then edit. To invoke the compiler, call dotnet build (or dotnet run, which will compile and then run the program). The output will be written to a subdirectory under bin\debug, which will include MyFirst‐ Program.dll (the output assembly) as well as MyFirstPro‐ gram.exe (which runs the compiled program directly). 4 | C# 9.0 Pocket Reference