C sharp 8.0 new features

Who Am I?
Miguel has over 10 years of experience with
Microsoft Technologies. Specialized with many
things in the Microsoft ecosystem, including C#,
F#, and Azure, he likes to blog about his
engineering notes and technology in general. He
is also very involved in the Montréal msdevmtl
community where he is a co-organizer.
NEXUS INNOVATIONS - PRÉSENTATION 2
https://blog.miguelbernard.com
https://www.linkedin.com/in/miguelbernard/
@MiguelBernard88
https://github.com/mbernard

New features
• Readonly members
• Default interface methods
• Pattern matching enhancements
• Using declarations
• Static local functions
• Disposable ref structs
• Nullable reference types
• Asynchronous streams
• Indices and ranges
• Null-coalescing assignment
• Unmanaged constructed types
• Stackalloc in nested expressions
• Enhancement of interpolated verbatim strings

Nullable reference types
To enable it
• In .csproj
• <LangVersion>8.0</LangVersion>
• <Nullable>Enable</Nullable>
• In code
• #nullable enable
• #nullable restore

? nullable operator
! Null forgiving operator
i.e.
string? a = null;
a!.Length;

DEMO

Pattern matching enhancements
Use case of a Toll service
V1 -Price per vehicle type
• 🚗Car -> 2$
• 🚕Taxi -> 3.50$
• 🚌Bus -> 5$
• 🚚Truck -> 10$

V2 - Price considering occupancy
• Car and taxi
• No passengers -> +0.50 $
• 2 passengers -> -0.50 $
• 3 or more passengers -> -1$

V3 - Price considering occupancy
• Car and taxi
• No passengers -> +0.50 $
• 2 passengers -> -0.50 $
• 3 or more passengers -> -1$
• Bus
• Less than 50% full -> +2$
• More than 90% full -> -1$

V4 - Price considering weight
• > 5000 lbs -> +5$
• < 3000 lbs -> -2$

V5 – Refactor Car and Taxi!

Asynchronous streams
To have an async stream you need 3 properties
• It’s declared with the ‘async’ modifier
• It returns an IAsyncEnumerable<T>
• The method contains ‘yield return’ statements

Asynchronous streams
internal async IAsyncEnumerable<int> GenerateSequence()
{
for (int i = 0; i < 20; i++)
{
// every 3 elements, wait 2 seconds:
if (i % 3 == 0)
await Task.Delay(3000);
yield return i;
}
}
internal async Task<int> ConsumeStream()
{
await foreach (var number in GenerateSequence())
{
Console.WriteLine($"The time is {DateTime.Now:hh:mm:ss}. Retrieved {number}");
}
return 0;
}

Indices and ranges
New operators
• The index from end operator ^, which specifies that an index is relative to the
end of the sequence
• The range operator .., which specifies the start and end of a range as its
operands

Indices and ranges
Notes
• The ^0 index is the same as sequence[sequence.Length].
• Note that sequence[^0] does throw an exception, just as
sequence[sequence.Length] does
• For any number n, the index ^n is the same as sequence.Length – n
• The range [0..^0] represents the entire range, just as [0..sequence.Length]
represents the entire range.

Indices and ranges
private string[] words = new string[]
{
// index from start index from end
"The", // 0 ^9
"quick", // 1 ^8
"brown", // 2 ^7
"fox", // 3 ^6
"jumped", // 4 ^5
"over", // 5 ^4
"the", // 6 ^3
"lazy", // 7 ^2
"dog" // 8 ^1
};

Indices and ranges
var allWords = words[..]; // contains "The" through "dog".
var firstPhrase = words[..4]; // contains "The" through "fox"
var lastPhrase = words[6..]; // contains "the, "lazy" and "dog"
var lazyDog = words[^2..^0];
Index the = ^3;
words[the];
Range phrase = 1..4;
words[phrase];

Default interface methods
Demo!

Static local functions
int M()
{
int y = 5;
int x = 7;
return Add(x, y);
static int Add(int left, int right) => left + right;
}
You can now add the static modifier to local functions to ensure that local function doesn't capture (reference) any
variables from the enclosing scope.
Doing so generates CS8421, "A static local function can't contain a reference to <variable>."

Null-coalescing assignment
C# 8.0 introduces the null-coalescing assignment operator ??=. You can use
the ??= operator to assign the value of its right-hand operand to its left-hand
operand only if the left-hand operand evaluates to null.
List<int> numbers = null;
int? a = null;
(numbers ??= new List<int>()).Add(5);
Console.WriteLine(string.Join(" ", numbers)); // output: 5
numbers.Add(a ??= 0);
Console.WriteLine(string.Join(" ", numbers)); // output: 5 0
Console.WriteLine(a); // output: 0

Using declarations
Using variables are automatically disposed at the end of the current scope
public void Method()
{
using var file = new StreamWriter(“myFile.txt”);
…logic here…
} // Disposed here
public void Method()
{
using(var file = new StreamWriter(“myFile.txt”))
{
…logic here…
} // Disposed here
}

Enhancement of interpolated verbatim strings
Order of the $ and @ tokens in interpolated verbatim strings can be any: both
$@"..." and @$"..." are valid interpolated verbatim strings
In earlier C# versions, the $ token must appear before the @ token

Readonly members
• Only applicable for struct
• Advantages
• The compilier can now enforce your
intent
• Doing so will enable to compiler to
perform performance optimizations on
your code
public struct Point
{
public double X { get; set; }
public double Y { get; set; }
public readonly double Distance =>
Math.Sqrt(X * X + Y * Y);
public readonly override string ToString() =>
$"({X}, {Y}) is {Distance} from the origin";
}

Unmanaged constructed types
public struct Coords<T> where T : unmanaged
{
public T X;
public T Y;
}
Span<Coords<int>> coordinates = stackalloc[]
{
new Coords<int> { X = 0, Y = 0 },
new Coords<int> { X = 0, Y = 3 },
new Coords<int> { X = 4, Y = 0 }
};

Stackalloc in nested expressions
Starting with C# 8.0, if the result of a stackalloc expression is of the Span<T>
or ReadOnlySpan<T> type, you can use the stackalloc expression in other
expressions
Span<int> numbers = stackalloc[] { 1, 2, 3, 4, 5, 6 };
var ind = numbers.IndexOfAny(stackalloc[] { 2, 4, 6 ,8 });
Console.WriteLine(ind); // output: 1

Disposable ref structs
A struct declared with the ref modifier may not implement any interfaces and so
can't implement IDisposable.
Therefore, to enable a ref struct to be disposed, it must have an accessible
`void Dispose()` method. This feature also applies to readonly ref struct
declarations.
ref struct Book
{
public void Dispose()
{
}
}

References
• https://github.com/mbernard/csharp8sample
• https://docs.microsoft.com/en-us/dotnet/csharp/whats-new/csharp-8
• https://docs.microsoft.com/en-us/dotnet/csharp/tutorials/default-interface-
methods-versions

Questions?
Questions?
https://blog.miguelbernard.com
https://www.linkedin.com/in/miguelbernard/
@MiguelBernard88
https://github.com/mbernard

1751 Richardson, suite, 4.500
H3K 1G6, Montréa, Canada

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