1.
What’s new in C# 8?
Damir Arh

2.
Agenda
New features
Nullable reference types
Improvements to pattern matching
Asynchronous streams
Default interface members
Ranges and indexes
Technical requirements

3.
Nullable reference types
Tony Hoare:
“I call it my billion-dollar mistake. It was the invention of the null reference in
1965.”
Null-safety through static analysis
Syntactically similar to nullable value types
Requires opt-in

4.
Nullable reference types
DEMO

5.
Nullability in existing projects
Two approaches
Opt-in project, opt-out files
Opt-in files one by one
There’s more to it:
notnull generic constraint
Precondition attributes
Postcondition attributes
Flow attributes
More details: http://bit.ly/NullableAnnotations

6.
Pattern matching
Originally introduced in C# 7
Enhanced in C# 8
Tuple patterns
Property patterns
Positional patterns
Switch expression

7.
Pattern matching
DEMO

8.
Asynchronous streams
Iterators:
IEnumerable, IEnumerator, yield return
Asynchronous methods:
async, await, Task
Asynchronous streams:
IAsyncEnumerable, IAsyncEnumerator, yield return
async, await

9.
Asynchronous streams
DEMO

10.
Asynchronous streams in use
API controller action methods in ASP.NET Core 3.0
Asynchronous query results in EF Core 3.0
LINQ methods in Ix.NET

11.
Default interface members
Default method implementation in interface
Why?
Extend interface without breaking existing implementations
Trait-like composition without multiple inheritance

12.
Default interface members
DEMO

13.
Ranges and Indexes
New types: Range, Index
New expression syntax for both
Implicit indexer syntax for existing types

14.
Ranges and indexes
DEMO

15.
Ranges and indexes cheat sheet
array 0 1 2 3 4 5
i 0 1 2 3 4 5
Length – i ^6 ^5 ^4 ^3 ^2 ^1
[ 1..5 )
Start: inclusive End: exclusive

16.
Can I use C# 8 in my project?
Supported in all popular IDEs
Requires .NET Standard 2.1
.NET Core 3.0+
UWP, Xamarin, Unity, Mono
No support in .NET framework

17.
What about class libraries?
Recommended target: .NET Standard 2.0
Reasons against it:
Platform-specific application model
C# 8 features
Nullable annotations
Not available in .NET Standard 2.0
Use multi-targeting

18.
Resources
What’s new in C# 8.0
http://bit.ly/Cs8WhatsNew
Visual C# Archives | .NET Blog
http://bit.ly/DotNetBlogCSharp
Language Feature Status
http://bit.ly/RoslynLanguageRoadmap
The Absolutely Awesome Book on C# and .NET
https://www.dotnetcurry.com/csharpbook/