What’s next for .NET Core and C#

Bertrand Le Roy

Agenda• Tooling• .NET Standard• C#

.NET Core everywhere• Windows• macOS• Ubuntu, Debian, CentOS, RHEL, openSUSE, Fedora, …• Docker• X86, x64, ARM

Tooling• Visual Studio 2017• OmniSharp: VS Code, vim, emacs, Sublime, etc.• Visual Studio for Mac• JetBrains Rider• CLI: x-plat, focused on building code for both humans

and machines…

Project system• project.json will be gone for good with the 1.0 of the tooling• New and improved csproj• Small• Easy to manually edit• Globs – easier merges!• No GUIDs• Lower concept count• Integrated package references• Easily migrated from project.json• One project system to rule Xamarin, Mono, .NET Core, .NET

Framework• All the power of MSBuild

Default console app template…<Project Sdk="Microsoft.NET.Sdk"> <PropertyGroup> <OutputType>Exe</OutputType> <TargetFramework>netcoreapp1.0</TargetFramework> </PropertyGroup></Project>

… with a package<Project Sdk="Microsoft.NET.Sdk"> <PropertyGroup> <OutputType>Exe</OutputType> <TargetFramework>netcoreapp1.0</TargetFramework> </PropertyGroup>

<ItemGroup> <PackageReference Include="Newtonsoft.JSON" Version="9.0.1" />

</ItemGroup></Project>

Default library template<Project Sdk="Microsoft.NET.Sdk"> <PropertyGroup>

<TargetFramework>netstandard1.4</TargetFramework> </PropertyGroup></Project>

Introducing the SDK• Contains all the tasks and targets for working with Core

code• Shared between CLI, Visual Studio, Visual Studio for

Mac, VS Code (OmniSharp)

Shared SDK component

Visual Studio VS Code.NET Core

Command Line tools

CLI commands

dotnet build --output [path]

the driver verb (command) verb arguments

Core commands• dotnet new• dotnet restore• dotnet run• dotnet build• dotnet publish• dotnet pack• dotnet test

CRUD & advanced commands• dotnet add/list/remove reference• dotnet add/list/remove package• dotnet sln add/list/remove• dotnet msbuild• dotnet nuget• dotnet vstest

• … and your own commands, distributed as NuGet packages or added to the path

.NET before .NET Standard .NET FRAMEWORK .NET CORE XAMARIN

APP

MO

DELS

BASE

LIBR

ARIE

S

Compilers Languages Runtime components

COMMON INFRASTRUCTURE

Base Class Library Core Library Mono Class Library

ASP.NET

Windows FormsWPF UWP

ASP.NET Core

iOSAndroid

OS X

.NET before .NET Standard .NET FRAMEWORK .NET CORE XAMARIN

APP

MO

DELS

BASE

LIBR

ARIE

S

Compilers Languages Runtime components

COMMON INFRASTRUCTURE

Base Class Library Core Library Mono Class Library

ASP.NET

Windows FormsWPF UWP

ASP.NET Core

iOSAndroid

OS XDifficult to reuse skills• Need to master 3+1 base class libraries

Difficult to reuse code• Need to target a small common denominator

Difficult to innovate• Need implementations on each platform

CHALLENGES

.NET after .NET Standard .NET FRAMEWORK .NET CORE XAMARIN

APP

MO

DELS

BASE

LIBR

ARIE

S

Compilers Languages Runtime components

COMMON INFRASTRUCTURE

Base Class Library Core Library Mono Class Library

ASP.NET

Windows FormsWPF UWP

ASP.NET Core

iOSAndroid

OS X

.NET STANDARDOne BCL to rule them all

.NET after .NET Standard .NET FRAMEWORK .NET CORE XAMARIN

APP

MO

DELS

BASE

LIBR

ARIE

S

Compilers Languages Runtime components

COMMON INFRASTRUCTURE

Base Class Library Core Library Mono Class Library

ASP.NET

Windows FormsWPF UWP

ASP.NET Core

iOSAndroid

OS X

.NET STANDARDOne BCL to rule them all

Reuse skills• Master one library, not a platform

Reuse code• Big surface area - no small common denominator

Faster innovation• .NET Standard can grow without updating platforms

BENEFITS

What is .NET Standard?• A spec: .NET Standard is to .NET what POSIX is to Unix

public class DotNetCore : IDotNetStandard { … }• A set of APIs that all .NET platforms have to implement• A class library provided as a NuGet package that

provides the façade that .NET code can compile against

Versioning .NET Standard• Higher version incorporates

all previous• Concrete .NET platforms

implement a specific version of the standard, and can run all code targeting versions up to that number

2.0

1.6

1.3

1.0

What’s new in .NET Standard 2.0?• More than double the APIs• Compatibility with .NET Framework libraries: your code

may already be cross-platform…

Version #APIs Growth %

1.6 13,501

2.0 32,638 +142%

APIs in .NET Standard 2.0

Primitives • Collections • Reflection • Interop • Linq

CORE

Threads • Thread Pool • TasksTHREADING

Files • Compression • MMFIO

Sockets • Http • Mail • WebSocketsNETWORKING

BinaryFormatter • Data Contract • XMLSERIALIZATION

XLinq • XML Document • XPath • Schema • XSL

XML

Abstractions • Provider Model • DataSetDATA

http://apisof.net

http://stackoverflow.com/research/developer-survey-2016#technology-most-popular-technologies

Most “popular” technologies

http://stackoverflow.com/research/developer-survey-2016#technology-most-loved-dreaded-and-wanted

Most “loved” technologies

C# - State of the Union• The lingua franca of .NET• Lead with C#• Keep up with (and move) industry state of the art• Focus on improvements for all C# developers• Innovate judiciously and responsibly

C# 1,000,000’sMillions

C# 7.0 recap

static void Main(string[] args){ object[] numbers = { 0b1, 0b10, new object[] { 0b100, 0b1000 }, // binary literals 0b1_0000, 0b10_0000 }; // digit separators

var (sum, count) = Tally(numbers); // deconstruction WriteLine($"Sum: {sum}, Count: {count}");}

C# 7.0 recapstatic (int sum, int count) Tally(object[] values) // tuple types{ var r = (s: 0, c: 0); // tuple literals void Add(int s, int c) { r.s += s, r.c += c; } // local functions foreach (var v in values) { switch (v) // switch on any value { case int i: // type patterns Add(i, 1); break; case object[] a when a.Length > 0: // case conditions var t = Tally(a); Add(t.sum, t.count); break; } } return r;}

What’s aheadNo clear shape of future versions yetMany ideas, and some stand out as clearly worthwhile

“Point” releases C# 7.1, 7.2, …Smaller, more frequent language versions that are opt-in for the cutting edge

C# 8.0, 9.0, …Major features requiring framework or runtime evolution

Design tenetsExpressivenessThe language embraces new concepts

ConvenienceCommon paths become easier

PerformanceCode runs faster or uses less memory

SafetyBugs are prevented

Recursive patterns

if (o is Point(_, var y)) { WriteLine($"Y: {y}"); }

if (o is Point { Y: var y }) { WriteLine($"Y: {y}"); }

Pattern matching expressionsvar s = match (o){ int i => $"Number {i}", case Point(int x, int y) => $"({x},{y})", string s when s.Length > 0 => s, null => "<null>", _ => "<other>"};

Tuples in patternsstate = match (state, request){ (Closed, Open) => Opened, (Closed, Lock) => Locked, (Opened, Close) => Closed, (Locked, Unlock) => Closed, _ => throw new InvalidOperationException(…)}

Nullable and non-nullable reference types

string? n; // Nullable reference typestring s; // Non-nullable reference type

n = null; // Sure; it's nullables = null; // Warning! Shouldn’t be null!s = n; // Warning! Really!

WriteLine(s.Length); // Sure; it’s not nullWriteLine(n.Length); // Warning! Could be null!

if (n != null) { WriteLine(n.Length); } // Sure; you checkedWriteLine(n!.Length); // Ok, if you insist!

Async streams and disposablesIAsyncEnumerable<Person> people = database.GetPeopleAsync();

foreach await (var person in people) { // use person}

using await (IAsyncDisposable resource = await store.GetRecordAsync(…)) { // use resource}

Default implementationspublic interface IEnumerator{ object Current { get; } bool MoveNext(); void Reset() => throw new InvalidOperationException("Reset not supported");}

public interface IEnumerator<out T> : IDisposable, IEnumerator{ new T Current { get; } object IEnumerator.Current => Current;}

Records and discriminated unionsclass Person : IEquatable<Person>{ public string First { get; } public string Last { get; }

public Person(string First, string Last) { this.First = First; this.Last = Last; }

public void Deconstruct(out string first, out string last) { first = First; last = Last; }

public bool Equals(Person other) => other != null && First == other.First && Last == other.Last; public override bool Equals(object obj) => obj is Person other ? Equals(other) : false; public override int GetHashCode() => GreatHashFunction(First, Last); …}

record Person(string First, string Last);

Primary constructorspublic class AccountController( UserManager<ApplicationUser> userManager, SignInManager<ApplicationUser> signInManager, ILogger<AccountController> logger) : Controller(){ public UserManager<ApplicationUser> UserManager => userManager; public SignInManager<ApplicationUser> SignInManager => signInManager; ///...}

Creating immutable objects

var p1 = new Point { X = 3, Y = 7 };

var p2 = p1 with { X = -p1.X };

Extension everythingextension Enrollee extends Person{ // static field static Dictionary<Person, Professor> enrollees = new();

// instance method public void Enroll(Professor supervisor) { enrollees[this] = supervisor; }

// instance property public Professor Supervisor => enrollees.TryGetValue(this, out var supervisor) ? supervisor : null;

// static property public static ICollection<Person> Students => enrollees.Keys;

// instance constructor public Person(string name, Professor supervisor) : this(name) { this.Enroll(supervisor); } }

Questions?