What is New in C# 6.0?

What is new in the new version 6.0 of the C# programming language?

Telerik Academy Plushttp://academy.telerik.com

C# 6.0 and Roslyn Seminar

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Used Software and Tools

Windows 10 (Tech Preview) Visual Studio "14" CTP 4

Roslyn Syntax Visualizer

ILSpy for decompiling thecompiled code

Documentation and Roslyn source code http://roslyn.codeplex.com/

Demo code available in GitHub: github.com/NikolayIT

/CSharp-6-New-Features

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History of the C# Language

C# 1.0VS

2002.NET 1.0

Managed Code

C# 2.0VS

2005.NET 2.0

Generics<T>

Reflection

Anonymous

Methods

Partial Class

Nullable Types

C# 3.0VS

2008.NET 3.5

Lambda Expressi

onLINQ

Anonymous

Types

Extension

Methods

Implicit Type (var)

C# 4.0VS

2010.NET 4.0

dynamicNamed Argume

nts

Optional Paramet

ers

More COM

Support

C# 5.0VS

2012.NET 4.5

Async / Await

Caller Informati

on

C# 6.0 VS 14.NET ?

A lot of new features….NET Compiler

Platform (Roslyn)

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Table of Contents What is new in C# 6.0?

Auto-property Enhancements Primary Constructors (dropped) Expressions as Function Body Using Static Exception Filters Declaration Expressions (inline

declarations) Nameof Expressions Null-conditional Operators Index Initializers Await in catch/finally Not Implemented, Yet

Auto-property Enhancements

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Initializers for Auto-Properties

You can add an initializer to an auto-property, just as you can to a field:

The initializer directly initializes the backing field

Just like field initializers, auto-property initializers cannot reference "this"

public class Person{ public string FirstName { get; set; } = "Nikolay"; public string LastName { get; set; } = "Kostov";}

this.<FirstName>k__BackingField = "Nikolay";

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Getter-Only Auto-Properties

Auto-properties can now be declared without a setter:

The backing field of a getter-only auto-property is implicitly declared as read-only:

It can be assigned to via property initializer In future releases it will be possible

to assign it in the declaring type’s constructor body

public string FirstName { get; } = "Nikolay";

.field private initonly string '<FirstName>k__BackingField'

Primary ConstructorsAllow constructor parameters to be declared directly on the class or struct,

without an explicit constructor declaration in the body of the type

declaration

Dropped

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Experimental Features Some of the features currently only work when the LangVersion of the compiler is set to “experimental” Adding the following line to the

csproj file in appropriate places (e.g. next to <WarnLevel>) will do the trick:<LangVersion>experimental</LangVersion>

<PropertyGroup> ... <LangVersion>experimental</LangVersion> </PropertyGroup>

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Parameters on Classes and Structs With primary constructor (C# 6.0)

Without primary constructor (C# 5.0)

public class Person(string firstName, string lastName){ public string FirstName { get; set; } = firstName; public string LastName { get; set; } = lastName;}public class Person { private string firstName; private string lastName; public Person(string first, string last) { firstName = first; lastName = last; } public string FirstName { get { return firstName; } } public string LastName { get { return lastName; } }}

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Primary Constructor Bodies

Sometimes there is a desire to do other things in constructor bodies, such as validate the constructor arguments:public class Person(string firstName, string lastName){ { if (firstName == null) throw new ArgumentNullException("firstName"); if (lastName == null) throw new ArgumentNullException("lastName"); } public string FirstName { get; } = firstName; public string LastName { get; } = lastName;}

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Explicit Constructors A class declaration with a primary constructor can still define other constructors

To ensure that arguments actually get passed to the primary constructor, all other constructors must call a this(…) initializer

The primary constructor is the only one that can call a base(…) initializer

public Person() : this ("Nikolay", "Kostov") { }

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Base Initializer The primary constructor always implicitly or explicitly calls a base initializer If no base initializer is specified, it

will default to calling a parameterless base constructor

The way to explicitly call the base initializer is to pass an argument list to a base class specifier

public class BufferFullException() : Exception("Buffer full"){}

Expression BodiedFunction Members

Lambda expressions can be declared with an expression body as well as a

conventional function body consisting of a block

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Expression as Method Body

Methods as well as user-defined operators and conversions can be given an expression body by use of the “lambda arrow”:

The effect is exactly the same as if the methods had had a block body with a single return statement For void returning methods -

expression following the arrow must be a statement

public object Clone() => new Point(this.X, this.Y);

public static Complex operator +(Complex a, Complex b) => a.Add(b);

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Expression as Property Getter

Expression bodies can be used to write getter-only properties and indexers where the body of the getter is given by the expression body

Note that there is no get keyword It is implied by the use of the

expression body syntax

public Person this[string name] => this.Children.FirstOrDefault( x => x.Name.Contains(name));

public string Name => FirstName + " " + LastName;

Using Static

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Using Static Allows specifying a static class in a using clause All its accessible static members

become available without qualificationusing System.Console;

using System.Math;class Program{ static void Main() { WriteLine(Pow(2, 10)); }}

Exception Filters

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Exception Filters If the parenthesized expression evaluates to true, the catch block is run

Already available in VB.NET and F#

try{ person = new Person("Nikolay", null);}catch(ArgumentNullException e) if(e.ParamName=="firstName"){ Console.WriteLine("First name is null");}catch(ArgumentNullException e) if(e.ParamName=="lastName"){ Console.WriteLine("Last name is null");}

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Logging with Exception Filters

We can use exception filters for side effects (e.g. logging)

Exception filters are preferable to catching and rethrowing (they leave the stack unharmed) You have access to the actual stack

when the exception araises

try { ... }catch (Exception ex) if (Log(ex)) { ... }

private static bool Log(Exception exception){ Console.WriteLine(exception.Message); return false;}

Declaration ExpressionsInline variable declarations.

Experimental feature. Currently suspended.

Dropped

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Declaration Expressions Declaration expressions allow you to declare local variables in the middle of an expression, with or without an initializer

The scope of the variables is to the nearest block or embedded statement (if-else)

if (int.TryParse(s, out int i)) { ... }

Console.WriteLine("Result: {0}", (var x = GetValue()) * x);if ((string str = obj as string) != null) { ... str ... }from s in stringsselect int.TryParse(s, out int i) ? i : -1;

Nameof Expressions

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Nameof Expressions Occasionally you need to provide a string that names some program element When throwing

ArgumentNullException

When raising a PropertyChanged event

When selecting controller name in MVC

nameof() = Compiler checks, navigation, easy for renaming (refactoring)

Still missing support for other classes [info]

if (x == null) throw new ArgumentNullException(nameof(x));

@Html.ActionLink("Sign up",nameof(UserController),"SignUp")

Null-conditional OperatorsNull-propagating operator ?.

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Null-conditional Operators

Lets you access members and elements only when the receiver is not-null Providing a null result otherwise

Can be used together with the null coalescing operator ??:

Can also be chained

int? length = customers?.Length; //null if customers is nullCustomer first = customers?[0]; //null if customers is null

int length = customers?.Length ?? 0; // 0 if customers null

int? first = customers?[0].Orders?.Count();

Index Initializers

Index Initializers A new syntax to object initializers allowing to set values to keys through the indexers

Before (C# 5.0)

Now (C# 6.0)

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var numbers = new Dictionary<int, string> { [7] = "seven", [9] = "nine", [13] = "thirteen"};

var numbers = new Dictionary<int, string> { { 7, "seven" }, { 9, "nine" }, { 13, "thirteen" }};

Await in catch/finally

Await in catch/finally In C# 5.0 using the await keyword in catch and finally blocks was not allowed This has actually been a significant

limitation In C# 6.0 await is now allowed in catch/finally

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var input = new StreamReader(fileName);var log = new StreamWriter(logFileName);try { var line = await input.ReadLineAsync();}catch (IOException ex) { await log.WriteLineAsync(ex.ToString());}finally { if (log != null) await log.FlushAsync();}

Not Implemented, YetNot implemented C# features as of

October 2014

Not Implemented, Yet Binary literals and digit separators

private protected – for derives in the assembly

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var bits = 0b00101110; var hex = 0x00_2E;var dec = 1_234_567_890;

protectedinternalprivate protected

protected internal private public

Not Implemented, Yet (2)

Indexed member initializer

Indexed member access

Equivalent to

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var obj = new JObject { $first = "N", $last = "K" }// Equivalent tovar obj = new JObject();obj["first"] = "N";obj["last"] = "K";

obj.$name = obj.$first + " " + obj.$last;

obj["name"] = obj["first"] + " " + obj["last"];

Not Implemented, Yet (3)

Params IEnumerable<>

Event initializers

Constructor Inference

Instead of

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decimal Avg(params IEnumerable<int> numbers) { … }

var tuple = new Tuple(3, "three", true);

var tuple = new Tuple<int,string,bool>(3, "three", true);

var fsw = new FileSystemWatcher { Changed += FswCh };

Not Implemented, Yet (4)

Semicolon operator

String interpolation

This feature is planned and probably will be released in the next CTP (5) of VS 14

More information: [link] Constructor assignment to getter-only auto-properties 36

var res = (var x = 4; Console.Write(x); x * x); // 16

var str = $"{hello}, {world}!";

// Instead ofvar str = string.Format("{0}, {1}!", hello, world);

int P { get; } public Class() { P = 15; }

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What is New in C# 6.0?

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