The document discusses new features in C# 8 including readonly members, default interface methods, pattern matching with switch expressions and property patterns, using declarations, static local functions, asynchronous streams with IAsyncEnumerable, and null-coalescing assignment. Some key features covered are readonly members to prevent modification of struct fields and methods, default interface methods to provide implementation in interfaces, switch expressions as a cleaner alternative to switch statements, and property patterns for matching on property values in a switch expression.

1. Novedades de C# 8
• Germán Küber
• Software Architect & Developer
NET-Baires
http://germankuber.com.ar
@germankuber
germankuber

2. Readonly members

3. public struct Point
{
public double X { get; set; }
public double Y { get; set; }
public double Distance => Math.Sqrt(X * X + Y * Y);
public override string ToString() =>
$"({X}, {Y}) is {Distance} from the origin";
}

4. public struct Point
{
public double X { get; set; }
public double Y { get; set; }
public double Distance => Math.Sqrt(X * X + Y * Y);
public readonly override string ToString() =>
$"({X}, {Y}) is {Distance} from the origin";
}

5. 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";
}

6. public readonly void Translate(int xOffset,
int yOffset)
{
X += xOffset;
Y += yOffset;
}

7. Default interface methods

8. public interface ICustomer
{
IEnumerable<IOrder> PreviousOrders { get; }
DateTime DateJoined { get; }
}

9. public interface ICustomer
{
IEnumerable<IOrder> PreviousOrders { get; }
DateTime DateJoined { get; }
public decimal ComputeLoyaltyDiscount()
{
DateTime TwoYearsAgo = DateTime.Now.AddYears(-2);
if ((DateJoined < TwoYearsAgo)
&& (PreviousOrders.Count() > 10))
{
return 0.10m;
}
return 0;
}
}

10. var customer = new Customer();
customer.ComputeLoyaltyDiscount();
ICustomer customer2 = new Customer();
customer2.ComputeLoyaltyDiscount();

11. public class Customer : ICustomer
{
public IEnumerable<IOrder> PreviousOrders { get; set; }
public DateTime DateJoined { get; set; }
}

12. public class Customer : ICustomer
{
public IEnumerable<IOrder> PreviousOrders { get; set; }
public DateTime DateJoined { get; set; }
public decimal ComputeLoyaltyDiscount()
{
return default;
}
}

13. public interface ICustomer
{
public static void SetLoyaltyThresholds(int minimumOrders = 10)
{
orderCount = minimumOrders;
}
private static int orderCount = 10;
private static decimal discountPercent = 0.10m;
public decimal ComputeLoyaltyDiscount()
{
//...
}
}

14. ICustomer customer2 = new Customer();
ICustomer.SetLoyaltyThresholds(12);
customer2.ComputeLoyaltyDiscount();

15. Pattern matching

16. Switch expressions

17. public enum Rainbow
{
Red,
Orange,
Yellow,
Green,
Blue,
Indigo,
Violet
}

18. public static RGBColor FromRainbowClassic(Rainbow colorBand)
{
switch (colorBand)
{
case Rainbow.Red:
return new RGBColor(0xFF, 0x00, 0x00);
case Rainbow.Orange:
return new RGBColor(0xFF, 0x7F, 0x00);
case Rainbow.Yellow:
default:
throw new ArgumentException();
};
}

19. public static RGBColor FromRainbow(Rainbow colorBand) =>
colorBand switch
{
Rainbow.Red => new RGBColor(0xFF, 0x00, 0x00),
Rainbow.Orange => new RGBColor(0xFF, 0x7F, 0x00),
Rainbow.Yellow => new RGBColor(0xFF, 0xFF, 0x00),
Rainbow.Green => new RGBColor(0x00, 0xFF, 0x00),
Rainbow.Blue => new RGBColor(0x00, 0x00, 0xFF),
Rainbow.Indigo => new RGBColor(0x4B, 0x00, 0x82),
Rainbow.Violet => new RGBColor(0x94, 0x00, 0xD3),
_ => throw new ArgumentException(),
};

20. Property patterns

21. public static decimal ComputeSalesTax(Address location,
decimal salePrice) =>
location switch
{
{ State: "WA" } => salePrice * 0.06M,
{ State: "MN" } => salePrice * 0.75M,
{ State: "MI" } => salePrice * 0.05M,
_ => 0M
};

22. Using declarations

23. int WriteLinesToFile(IEnumerable<string> lines)
{
int skippedLines = 0;
using (var file = new StreamWriter("WriteLines2.txt"))
{
foreach (string line in lines)
{
}
} // file is disposed here
return skippedLines;
}

24. nt WriteLinesToFile(IEnumerable<string> lines)
{
using var file = new StreamWriter("WriteLines2.txt");
int skippedLines = 0;
foreach (string line in lines)
{
}
return skippedLines;
// file is disposed here
}

25. Static local functions

26. int M()
{
int y;
LocalFunction();
return y;
void LocalFunction() => y = 0;
}

27. int M()
{
int y = 5;
int x = 7;
return Add(x, y);
static int Add(int left, int right) => left + right;
}

28. Asynchronous streams

29. Asynchronous streams
• Se declara con el modificador async
• Devuelve IAsyncEnumerable<T>
• Contiene instrucciones yield
• Utilizar await delante del foreach

30. public static async IAsyncEnumerable<int> GenerateSequence()
{
for (int i = 0; i < 20; i++)
{
await Task.Delay(100);
yield return i;
}
}

31. await foreach (var number in GenerateSequence())
{
Console.WriteLine(number);
}

32. Indices and ranges

33. Asynchronous streams
• System.Index representa un índice en una secuencia.
• índice desde el operador final ^
• System.Range representa un subrango de una secuencia.
• El operador de intervalo ..

34. var 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
}; // 9 (or words.Le

35. Recuperar última palabra
Console.WriteLine($"The last word is {words[^1]}");

36. Recupera un subrango
string[] quickBrownFox = words[1..4];

37. Incluye words[^2] y words[^1]
var lazyDog = words[^2..^0];

38. Null-coalescing assignment

39. ??=

40. List<int> numbers = null;
int? i = null;
numbers ??= new List<int>();
numbers.Add(i ??= 17);
numbers.Add(i ??= 20);
Console.WriteLine(string.Join(" ", numbers)); // output:
17 17
Console.WriteLine(i); // output: 17

41. Gracias !!!
• Germán Küber
• Software Architect & Developer
NET-Baires
http://germankuber.com.ar
@germankuber

42. Recursos
• https://www.germankuber.com.ar/novedades-en-c-8/
• https://docs.microsoft.com/en-us/dotnet/csharp/whats-new/csharp-
8
• https://www.youtube.com/watch?v=L2BvrXnaOy0
• https://www.youtube.com/watch?v=VdC0aoa7ung