The document summarizes features in C# 10 and beyond, including records, required properties, parameter null checking, pattern matching, lambda improvements, and value tuple deconstruction. It also discusses how to run samples and provides information about the presenter, Moaid Hathot. Key C# 10 features covered are records, properties, parameter null checking, pattern matching, and lambda improvements. The document promotes less code through features like file-scoped namespaces and global using directives. It concludes with a discussion of abstract data types and static abstract members in interfaces.

1. Best of //Build 2021
C# 10, .NET 6 & Beyond
Moaid Hathot
Senior Software Engineer @ Microsoft | ex-Azure MVP
Moaid.Hathot@outlook.com
@MoaidHathot
https://moaid.codes
https://meetup.com/Code-Digest

2.  Some features are still under development
 Feature, design, and status
C# 10 features

3.  Records
 Record structs
 Sealed ToString
 Properties & Parameters improvements
 Required Properties
 ‘field’ keyword
 Parameter null-checking
 Pattern matching
 List Patterns
 Extended Property Patterns
 Cleaner code
 File-scoped namespaces
 File-scoped namespaces
 Global using directives
 Lambdas improvements
 ValueTuple deconstruction
 Deconstruction of ‘default’ literal
 Mix declaration and variables in deconstruction
 ADT – Abstract Data types
C# 10 and beyond

4.  How to run the samples
 .NET 6 SDK Preview 5
 Visual Studio 2022 Preview + Roslyn feature branches
 LinqPad 6 beta (not all features)
 SharpLab.io
C# 10 and beyond

5. About Moaid Hathot
 Senior software Engineer @ Microsoft
 Ex-Azure MVP
 Software Craftsmanship advocate
 Clean Coder
 Co-Founder of Code.Digest();
 https://meetup.com/Code-Digest
Moaid Hathot

6. C# feature
Record Improvements

7. Records
public record Person
{
public string FirstName { get; init; }
public string LastName { get; init; }
}

8. Records
public class Person : IEquatable<Person>
{
public string FirstName { get; init; }
public string LastName { get; init; }
public override bool Equals(object obj)
=> Equals(obj as Person);
public bool Equals(Person other)
=> other is { } && (FirstName, LastName) == (other.FirstName, other.LastName);
public override int GetHashCode()
=> (FirstName, LastName).GetHashCode();
public override string ToString()
=> $"FirstName: '{FirstName}', LastName: '{LastName}'";
public static bool operator ==(Person first, Person second)
=> object.ReferenceEquals(first, second) || (first is { } && first.Equals(second));
public static bool operator !=(Person first, Person second)
=> !(first == second);
public void Deconstruct(out string firstName, out string lastname)
=> (firstName, lastname) = (FirstName, LastName);
}

9. Records
public record Person
{
public string FirstName { get; init; }
public string LastName { get; init; }
}

10. Records
public record Person(string FirstName, string LastName);

11. Records
public record Person(string FirstName, string LastName);
var moaid = new Person("Moaid", "Hathot");

12. Records
public record Person(string FirstName, string LastName);
var moaid = new Person("Moaid", "Hathot");
var wifu = moaid with { FirstName = "Haneeni" };
var clone = moaid with { };

13. Records
public record Person(string FirstName, string LastName);

14. Records
public record Person(string FirstName, string LastName);
public record struct Person(string FirstName, string LastName);

15. Records
public record Person(string FirstName, string LastName);
public record struct Person(string FirstName, string LastName);
public record class Person(string FirstName, string LastName);

16. C# feature
Property Improvements

17. Required Properties
public class Person
{ … }

18. Required Properties
public class Person
{ … }
var moaid = new Person("Moaid", "Hathot");

19. Required Properties
public class Person
{ … }
var moaid = new Person("Moaid", "Hathot");
var moaid = new Person
{
FirstName = "Moaid",
LastName = "Hathot"
}

20. Required Properties
public class Person
{
public string FirstName { get; }
public string LastName { get; }
public Person(string firstName, string lastName)
{
FirstName = firstName;
LastName = lastName;
}
}
var moaid = new Person("Moaid", "Hathot");

21. Required Properties
public class Person
{
public string FirstName { get; }
public string LastName { get; }
public Person(string firstName, string lastName)
{
FirstName = firstName;
LastName = lastName;
}
}
var moaid = new Person("Moaid", "Hathot");
var moaid = new Person
{
FirstName = "Moaid",
LastName = "Hathot"
}

22. Required Properties
public class Person
{
public string FirstName { get; set; }
public string LastName { get; set; }
public Person(string firstName, string lastName)
{
FirstName = firstName;
LastName = lastName;
}
public Person()
{
}
}

23. Required Properties
public class Person
{
public string FirstName { get; init; }
public string LastName { get; init; }
public Person(string firstName, string lastName)
{
FirstName = firstName;
LastName = lastName;
}
public Person()
{
}
}

24. Required Properties
public class Person
{
public string FirstName { get; init; }
public string LastName { get; init; }
public Person(string firstName, string lastName)
{
FirstName = firstName;
LastName = lastName;
}
public Person()
{
}
}
var moaid = new Person();

25. Required Properties
public class Person
{
public required string FirstName { get; init; }
public required string LastName { get; init; }
public Person(string firstName, string lastName)
{
FirstName = firstName;
LastName = lastName;
}
public Person()
{
}
}

26. Required Properties
public class Person
{
public required string FirstName { get; init; }
public required string LastName { get; init; }
}
var moaid = new Person
{
FirstName = "Moaid",
LastName = "Hathot"
}

27. Property fields
public class Person
{
public string Name { get; set; }
}

28. Property fields
public class Person
{
private string _name;
public string Name
{
get => _name;
set => _name = value?.ToLower();
}
}

29. Property fields
public class Person
{
public string Name
{
get;
set => field = value?.ToLower();
}
}

30. C# feature
Parameter null-checking

31. Parameter null-checking
void SayHello(Person person)
{
if(person is null)
{
throw new NullReferenceException();
}
Console.WriteLine($"Hello {person.FirstName}");
}

32. Parameter null-checking
void SayHello(Person person)
{
_ => person ?? throw new NullReferenceException();
Console.WriteLine($"Hello {person.FirstName}");
}

33. Parameter null-checking
void SayHello(Person person!!)
{
Console.WriteLine($"Hello {person.FirstName}");
}

34. C# feature
Pattern Matching

35. Extended property patterns
string obj = null;

36. Extended property patterns
string obj = null;
if (obj is { })
{
Console.WriteLine(obj);
}

37. Extended property patterns
string obj = null;
if (obj is { Length: var length })
{
Console.WriteLine(length);
}

38. Extended property patterns
string obj = null;
if (obj is { Length: 10 })
{
Console.WriteLine(10);
}

39. Extended property patterns
string obj = null;
if (obj is { Length: > 3 })
{
Console.WriteLine("> 3");
}

40. Extended property patterns
var moaid = new Person("Moaid", "Hathot");

41. Extended property patterns
var moaid = new Person("Moaid", "Hathot");
if (moaid is { FirstName: { Length: > 3 } })
{
}

42. Extended property patterns
var moaid = new Person("Moaid", "Hathot");
if (moaid is { FirstName: { Length: > 3 } })
{
}
if (moaid is { FirstName.Length: > 3 })
{
}

43. List Patterns
var arr = new []{ 1, 2, 3 };

44. List Patterns
var arr = new []{ 1, 2, 3 };
switch(arr)
{
case [_, 1, ..]: { }
case [.., 1, _]: { }
}

45. List Patterns
var arr = new []{ 1, 2, 3 };
switch(arr)
{
case [_, 1, ..]: { } // expr.Length is >= 2 && expr[1] is 1
case [.., 1, _]: { } // expr.Length is >= 2 && expr[^2] is 1
}

46. List Patterns
var arr = new []{ 1, 2, 3 };
arr is [1, 2, 3]

47. List Patterns
var arr = new []{ 1, 2, 3 };
arr is [1, 2, 3]
expr.Length is 3
&& expr[0] is 1
&& expr[1] is 2
&& expr[2] is 3

48. List Patterns
var arr = new []{ 1, 2, 3 };
arr is [1, .. var s, 3]

49. List Patterns
var arr = new []{ 1, 2, 3 };
arr is [1, 2, 3]
expr.Length is >= 2
&& expr[0] is 1
&& expr[1..^1] is var s
&& expr[^1] is 3

50. List Patterns
var arr = new []{ 1, 2, 3 };
arr is [1, 2, 3]
expr.Length is >= 2
&& expr[0] is 1 //expr[new Index(1, true)]
&& expr[1..^1] is var s //expr[new Range(1, new Index(1, true))]
&& expr[^1] is 3 //expr[new Index(1, true)]

51. List Patterns
IEnumerable<int> collection = ...

52. List Patterns
IEnumerable<int> collection = ...
_ = collection switch
{
{ 1 } => { }
{ 2 } => { }
{ .., 3 } => { }
};

53. C# feature
Less Code

54. File-scoped namespace
using System;
namespace BestOfBuild
{
public class Program
{
public static void Main()
{
Console.WriteLine("Hello World!");
}
}
}

55. File-scoped namespace
namespace BestOfBuild
using System;
public class Program
{
public static void Main()
{
Console.WriteLine("Hello World!");
}
}

56. File-scoped namespace
namespace BestOfBuild
public static void Main()
{
Console.WriteLine("Hello World!");
}

57. File-scoped namespace
public static void Main()
{
Console.WriteLine("Hello World!");
}

58. File-scoped namespace
Console.WriteLine("Hello World!");

59. Global using Directive
using System;
namespace BestOfBuild
{
public class Program
{
public static void Main()
{
Console.WriteLine("Hello World!");
}
}
}

60. Global using Directive
using System;
using System.Linq;
using System.Collections.Generic;
using System.Threading;
using System.Threading.Tasks;

61. Global using Directive
using System;
using System.Linq;
using System.Collections.Generic;
using System.Threading;
using System.Threading.Tasks;
using Human = BestOfBuild.Person;

62. Global using Directive
global using System;
global using System.Linq;
global using System.Collections.Generic;
global using System.Threading;
global using System.Threading.Tasks;
global using Human = BestOfBuild.Person;

63. Lambda Improvements
var action = () => { };
var func = () => 5;

64. Lambda Improvements
var action = () => { };
var func = () => 5;
Action action = () => { };
Func<int> func = () => 5;

65. Lambda Improvements
var func = () => 5;
Func<int> func = () => 5;

66. Lambda Improvements
var func = (): int => 5;
Func<int> func = (): int => 5;

67. Lambda Improvements
var func = [FromBody](): int => 5;
Func<int> func = (): int => 5;

68. ASP.NET MapActions
[HttpGet("/")] Todo GetTodo() => new(Id: 0, Name: "Name");
app.MapAction((Func<Todo>)GetTodo);
[HttpPost("/")] Todo PostTodo([FromBody] Todo todo) => todo;
app.MapAction((Func<Todo, Todo>)PostTodo);

69. ASP.NET MapActions
[HttpGet("/")] Todo GetTodo() => new(Id: 0, Name: "Name");
app.MapAction(GetTodo);
[HttpPost("/")] Todo PostTodo([FromBody] Todo todo) => todo);
app.MapAction(PostTodo);

70. ASP.NET MapActions
app.MapAction([HttpGet("/")] () => new Todo(Id: 0, Name: "Name"));
app.MapAction([HttpPost("/")] ([FromBody] Todo todo) => todo);

71. ASP.NET Minimal APIs
using System;
using Microsoft.AspNetcore.Builder;
record Person(string FirstName, string LastName);
var app = WebApplication.Create(args);
app.MapGet("/", () => new ("Moaid", "Hathot"));
await app.RunAsync();

72. ASP.NET Minimal APIs
using System;
using Microsoft.AspNetcore.Builder;
record Person(string FirstName, string LastName);
var app = WebApplication.Create(args);
app.MapGet("/", () => new Person("Moaid", "Hathot"));
await app.RunAsync();

73. ASP.NET Minimal APIs
using System;
using Microsoft.AspNetcore.Builder;
record Person(string FirstName, string LastName);
var app = WebApplication.Create(args);
app.MapGet("/", () => new Person("Moaid", "Hathot"));
await app.RunAsync();
const express = require('express');
const app = express();
app.get('/', (req, res) => {
res.send({ firstName: "Moaid", lastName: "Hathot"});
});
app.listen(3000, () => {
console.log(`App is listening`);
})

74. ASP.NET Minimal APIs
using Microsoft.AspNetcore.Builder;
record Person(string FirstName, string LastName);
var app = WebApplication.Create(args);
app.MapGet("/", () => new Person("Moaid", "Hathot"));
await app.RunAsync();
const express = require('express');
const app = express();
app.get('/', (req, res) => {
res.send({ firstName: "Moaid", lastName: "Hathot"});
});
app.listen(3000, () => {
console.log(`App is listening`);
})

75. ASP.NET Minimal APIs
using Microsoft.AspNetcore.Builder;
var app = WebApplication.Create(args);
app.MapGet("/", () => new Person("Moaid", "Hathot"));
await app.RunAsync();
const express = require('express');
const app = express();
app.get('/', (req, res) => {
res.send({ firstName: "Moaid", lastName: "Hathot"});
});
app.listen(3000, () => {
console.log(`App is listening`);
})

76. ASP.NET Minimal APIs
var app = WebApplication.Create(args);
app.MapGet("/", () => new Person("Moaid", "Hathot"));
await app.RunAsync();
const express = require('express');
const app = express();
app.get('/', (req, res) => {
res.send({ firstName: "Moaid", lastName: "Hathot"});
});
app.listen(3000, () => {
console.log(`App is listening`);
})

77. C# feature
Deconstruction Improvements

78. ValueTuple Deconstruction
record Person(string FirstName, string LastName);

79. ValueTuple Deconstruction
record Person(string FirstName, string LastName);
Person moaid = new ("Moaid", "Hathot");

80. ValueTuple Deconstruction
record Person(string FirstName, string LastName);
Person moaid = new ("Moaid", "Hathot");
var (firstName, lastName) = moaid;

81. ValueTuple Deconstruction
public class Person(string FirstName, string LastName);

82. ValueTuple Deconstruction
public class Person(string FirstName, string LastName)
{
public void Deconstruct(out string firstName, out string lastName)
{
firstName = FirstName;
lastName = LastName;
}
}

83. ValueTuple Deconstruction
var (firstName, lastName) = default;

84. ValueTuple Deconstruction
int (foo, bar) = default;

85. ValueTuple Deconstruction
int (foo, bar) = default;
(int foo, string bar) = default;

86. ValueTuple Deconstruction
(string firstName, string lastName) = default;

87. ValueTuple Deconstruction
string (firstName, lastName) = default;

88. ValueTuple Deconstruction
string (firstName, lastName) = default;
string firstName2;
string lastName2;
(firstName2, lastName2) = default;

89. ValueTuple Deconstruction
string (firstName, lastName) = default;
string firstName2;
string lastName2;
(firstName2, lastName2) = default;
string lastName3;
(var firstName3, lastName3) = default;

90. C# feature
ADT – Abstract Data Types

91. Static abstract members in interfaces
interface IAddable<T> where T : IAddable<T>
{
static abstract T Zero { get; }
static abstract T operator +(T t1, T t2);
}

92. Static abstract members in interfaces
interface IAddable<T> where T : IAddable<T>
{
static abstract T Zero { get; }
static abstract T operator +(T t1, T t2);
}
struct Int32 : …, IAddable<Int32>
{
static Int32 I.operator +(Int32 x, Int32 y) => x + y;
public static int Zero => 0;
}

93. Static abstract members in interfaces
interface IAddable<T> where T : IAddable<T>
{
static abstract T Zero { get; }
static abstract T operator +(T t1, T t2);
}
struct Int32 : …, IAddable<Int32>
{
static Int32 I.operator +(Int32 x, Int32 y) => x + y;
public static int Zero => 0;
}
public static T AddAll<T>(T[] ts) where T : IAddable<T>
{
T result = T.Zero; // Call static operator
foreach (T t in ts)
{
result += t; // Use `+`
}
return result;
}

94. Best of //Build 2021
Questions?
Moaid Hathot
Senior Software Engineer @ Microsoft | ex-Azure MVP
Moaid.Hathot@outlook.com
@MoaidHathot
https://moaid.codes
https://meetup.com/Code-Digest