Playing with recent and upcoming features from C# 8.0 through 11.0

Program.cs

// What's new in C#
// Good places to start:
// - https://docs.microsoft.com/dotnet/csharp/whats-new/csharp-version-history#c-version-72
// - https://docs.microsoft.com/dotnet/csharp/whats-new/csharp-11

#region implicit and global usings (C# 10)
global using Microsoft.EntityFrameworkCore;
global using System.Collections;
using System;
#endregion

#region top-level statements (C# 10)

Console.WriteLine("Waiting to start...");
// await Task.Delay(TimeSpan.FromMinutes(5));
Console.WriteLine("Hello team!");
#endregion

#region raw strings (C# 11)

// This is a raw string, new in C# 11 preview. No more pain pasting your JSON into code!
Console.WriteLine("""
    {
        "glossary": {
            "title": "example glossary",
            "GlossDiv": {
                "title": "S",
                "GlossList": {
                    "GlossEntry": {
                        "ID": "SGML",
                        "SortAs": "SGML",
                        "GlossTerm": "Standard Generalized Markup Language",
                        "Acronym": "SGML",
                        "Abbrev": "ISO 8879:1986",
                        "GlossDef": {
                            "para": "A meta-markup language, used to create markup languages such as DocBook.",
                            "GlossSeeAlso": ["GML", "XML"]
                        },
                        "GlossSee": "markup"
                    }
                }
            }
        }
    }
    """);

// What about interpolated strings?

Console.WriteLine($$$"""
    {
        "glossary": {
            "title": "example glossary",
            "GlossDiv": {
                "title": "{{{"S"}}}",
                "GlossList": {
                    "GlossEntry": {
                        "ID": "SGML",
                        "SortAs": "SGML",
                        "GlossTerm": "Standard Generalized Markup Language",
                        "Acronym": "SGML",
                        "Abbrev": "ISO 8879:1986",
                        "GlossDef": {
                            "para": "A meta-markup language, used to create markup languages such as DocBook.",
                            "GlossSeeAlso": ["GML", "XML"]
                        },
                        "GlossSee": "markup"
                    }
                }
            }
        }
    }
    """);

#endregion

#region interpolated string improvements
// See https://sharplab.io/#v2:EYLgtghglgdgNAExAagD4AEBMBGAsAKAPQGYACLc7AdgIG8DTHKA2cgFlIFloYAKASlIMmtIfiYTKABlLBSAXlIAiAB5KA3MMnTSAZwAuAJwWkAJEoi6EAM1rAAvhq2T02AJy8Dh/pvHax/qQAxgD2MAY6QSaqTn7aoeH6kWFeJuaWNrRBjr6Brh4JXj4EzvYE9kA===
#endregion

#region switch expressions (C# 8), caller argument expression (C# 10), list matching (C# 11)

var list = new[] { 1, 2, 3, 4 };
Describe(list);
Describe(new[] { 1, 2, 3 });
Describe(Array.Empty<int>());
Describe("I am not a list");

static void Describe<T>(T parameter, [System.Runtime.CompilerServices.CallerArgumentExpression("parameter")] string? name = default) =>
    Console.WriteLine($""" 
        The expression "{name}" represents { // multi-line expressions and comments in the interpolated string "holes" (C# 11)
            parameter switch
            {
                IList and [var a, var b, _] => $"a list of 3 elements, {a}, {b}, and some other element we don't care about",
                IList and [var a, ..] => $"a non-empty list that starts with {a}",
                IList and { Count: 0 } => "an empty list",
                _ => "something that isn't a list"
            }}.
        """);

#endregion

#region async streams (using EF Core) (C# 8), nullable reference types (C# 8), init-only settters (C# 9)

{  // Let's persist some data.
    using var context = new DatabaseContext(); // using declaration (gets disposed automatically at the end of the of scope)

    await context.Database.EnsureDeletedAsync();
    await context.Database.EnsureCreatedAsync();

    context.Add(
        new Person
        {
            Id = 1,
            PartitionKey = "1",
            FirstName = "John",
            LastName = "Doe"
        });

    context.Add(
        new Person
        {
            Id = 2,
            PartitionKey = "2",
            FirstName = "Jane",
            LastName = "Doe"
        });


    await context.SaveChangesAsync();
}

{ // Let's query some data.
    using var context = new DatabaseContext(); // using declaration (gets disposed automatically at then end of scope)

    // To see how foreach works, see https://sharplab.io/#v2:EYLgtghglgdgNAExAagD4AEBMBGAsAKHQAYACdbAOgBlYBHAbgIPQGYzMzsB2EgbyfwkhnAGxkALCQCy0GAAoAlHwLDVJAG4QATiQBmEANYBTAIoBXI1oCeJALwkYRgO4kA2gF0+AIghe4JL2A/AIBjLwBfCgBBAGdzSysIYAAbI0VGQTUhXQB7LSMIEIALOU0dIxJYPUNTC2sFFSzlTKbhAGEcmBic1IoAdS0oABc0owUM1vDGoSn8cKA==

    await foreach (var person in context.People.Where(p => p.LastName == "Doe").AsAsyncEnumerable().WithCancellation(default))
    {
        Console.WriteLine($"Here is a person: {person.FirstName} {person.LastName}");
    }
    Console.WriteLine();
}

public class Person
{
    public int Id { get; set; }
    // ! is the new "null-forgiving operator". 
    // Assigning default! signals the compiler we don't need to be warned that the non-nullable property isn't initialized.  
    public string PartitionKey { get; set; } = default!; 
    public string? FirstName { get; set; }
    public string LastName { get; set; } = default!; 
}

public class DatabaseContext : DbContext
{

    public DbSet<Person> People { get; init; } = default!; // Initialization-only settters

    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
        optionsBuilder.UseCosmos(
            "AccountEndpoint = https://localhost:8081/;AccountKey=C2y6yDjf5/R+ob0N8A7Cgv30VRDJIWEHLM+4QDU5DE2nQ9nDuVTqobD4b8mGGyPMbIZnqyMsEcaGQy67XIw/Jw==",
            "MyDatabase");
    }
}

#endregion

#region generic attributes (C# 11)

public class DefaultDatabaseValue<T> : Attribute
{

    public DefaultDatabaseValue(T value)
    {
        Value = value;
    }

    public T Value { get; }
}

public class PersonTest
{
    [DefaultDatabaseValue<int>(0)]
    public int Id { get; set; }

    [DefaultDatabaseValue<string>("J. Doe")]
    public string? Name { get; set; }
}

#endregion 

#region readonly struct members (C#8)

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

public struct Measure
{
    public readonly double Member { get; }
}
#endregion

#region records (C# 9)
// See https://sharplab.io/#v2:EYLgtghglgdgNAExAagD4AEBMBGAsAKAPQGYACLc7AdlIG8CDSnKA2cgFlIFloYAKAJR1GzUQAUApgCcAzgHsYAJQkBjOVISkADtPkxSAXlIwJAdz4AiAFIA6C3AsARORIsCA3CNFMv3gG4QUqQArloIEAAuEgiSsgqG2rrxplARABZ0pABiULIRAHIQYBIJ1hAmFqQAvp743sy+oujYAJx8jfWkACQWACppJaHhUZo6cTAA5DKkAGa5MhHGRSVQ0/R1naJDkdGxejY5eYXFVW61HT4b9c1tPRYWF960Y3pVpKvCV5vefC8KAIQGbYjPYKAD8pAsMDkiwsIEhbkeoiqEgAjsEIAAbOjA3ZJGBVJHMe5nXy+Qn4ClEMhSVTqTSgpR0jR8ZoABmy8wKyzglA5ABkIAtjhIPETvp1qaRaWoNKQAKJgLSYuQATwkJVZ2A5h2FPL5pEFeuKvPZCqVKvVUgE8N8jOUsoQfF13JNhqFrtFtSAA=
#endregion

#region UTF8 strings
// See https://sharplab.io/#v2:EYLgtghglgdgNAExAagD4AEBMBGAsAKAPQGYACLc7AdlIG8CDSnKA2cgFlIFloYAKAJR1GzUcACeAFwCmAbQC6pAK6SAZgA4AypIBOsAOakAvKQBEACWkAbKwHtSAVQAqAMXWltemPoDOAQlMldQBuEVEmdGwATj4VDU8DAVD8UQBfMNICVKA===
#endregion

#region default interface methods (C# 8)
// See https://docs.microsoft.com/dotnet/csharp/whats-new/csharp-8#default-interface-methods
#endregion

#region indices and ranges (C#8)
// See https://docs.microsoft.com/dotnet/csharp/whats-new/csharp-8#indices-and-ranges
#endregion

TestCSharp.csproj

<Project Sdk="Microsoft.NET.Sdk">

	<PropertyGroup>
		<OutputType>Exe</OutputType>
		<TargetFramework>net6.0</TargetFramework>
		<ImplicitUsings>enable</ImplicitUsings>
		<Nullable>enable</Nullable>
		<LangVersion>11</LangVersion>
		<EnablePreviewFeatures>True</EnablePreviewFeatures>
	</PropertyGroup>

	<ItemGroup>
	  <None Include="..\.editorconfig" Link=".editorconfig" />
	</ItemGroup>

	<ItemGroup>
	  <PackageReference Include="Microsoft.EntityFrameworkCore.Cosmos" Version="7.0.0-preview*" />
	</ItemGroup>

</Project>