First preview version of .NET 10.0 extends the class libraries

CUI.H2("--- LeftJoin ALT seit .NET Framework 3.5 ---");

var AllCompaniesWithWebsitesSetOld = outer
  .GroupJoin(inner,
             c => c.ID,
             w => w.CompanyID,
             (c, websites) => new { Company = c, Websites = websites })
  .SelectMany(
    x => x.Websites.DefaultIfEmpty(),  // Falls keine Webseite existiert, wird `null` verwendet
    (c, w) => new WebsiteWithCompany
    {
      Name = c.Company.Name,
      URL = w.URL,   // Falls `w` null ist, bleibt URL null
      City = c.Company.City
    });

foreach (var item in AllCompaniesWithWebsitesSetOld)
{
  Console.WriteLine((item.Name != null ? item.Name + " " + item.City : 
    "- keine Firma - ") + " -> " + (item.URL ?? "- keine URL -"));
}

CUI.H2("--- LeftJoin NEU ab .NET 10.0 ---");
var AllCompaniesWithWebsitesSet = outer.LeftJoin(inner, e => e.ID, e => e.CompanyID, (c, w) 
  => new WebsiteWithCompany { Name = c.Name, City = c.City, URL = w.URL });
foreach (var item in AllCompaniesWithWebsitesSet)
{
  Console.WriteLine((item.Name != null ? item.Name + " " + item.City :
    "- keine Firma - ") + " -> " + (item.URL ?? "- keine URL -"));
}

CUI.H2("--- RightJoin OLD seit .NET Framework 3.5  ---");
var WebsiteWithCompanySetOLD = inner
  .GroupJoin(outer,
             w => w.CompanyID,
             c => c.ID,
             (w, companies) => new { Website = w, Companies = companies })
  .SelectMany(
    x => x.Companies.DefaultIfEmpty(),  // Falls kein Unternehmen existiert, bleibt `null`
    (w, c) => new WebsiteWithCompany
    {
      Name = c.Name,  // Falls `c` null ist, bleibt `Name` null
      City = c.City,   // Falls `c` null ist, bleibt `City` null
      URL = w.Website.URL
    });

foreach (var item in WebsiteWithCompanySetOLD)
{
  Console.WriteLine((item.Name != null ? item.Name + " " + item.City : 
    "- keine Firma - ") + " -> " + (item.URL ?? "- keine URL -"));
}

CUI.H2("--- RightJoin NEU ab .NET 10.0 ---");
var WebsiteWithCompanySet = outer.RightJoin(inner, e => e.ID, e => e.CompanyID, (c, w) 
  => new WebsiteWithCompany { Name = c.Name, City = c.City, URL = w.URL });

foreach (var item in WebsiteWithCompanySet)
{
  Console.WriteLine((item.Name != null ? item.Name + " " + item.City :
    "- keine Firma - ") + " -> " + (item.URL ?? "- keine URL -"));
}

// Zum Vergleich: Inner Join, den es seit .NET Framework 3.5 gibt
CUI.H2("--- InnerJoin seit .NET Framework 3.5 ---");
var CompaniesWithWebsitesSet = outer.Join(inner,
                                          c => c.ID,
                                          w => w.CompanyID,
                                          (c, w) => new WebsiteWithCompany
                                          {
                                            Name = c.Name,
                                            URL = w.URL,
                                            City = c.City
                                          });
foreach (var item in CompaniesWithWebsitesSet)
{
  Console.WriteLine((item.Name != null ? item.Name + " " + item.City : 
    "- keine Firma - ") + " -> " + (item.URL ?? "- keine URL -"));
}

OrderedDictionary<string, string> websites = new OrderedDictionary<string, string>();
websites.Add("Heise", "www.Heise.de");
websites.Add("Microsoft", "www.Microsoft.com");
websites.Add("IT-Visions", "www.IT-Visions.de");

var propertyName = "IT-Visions";
var value = "www.IT-Visions.de";

// bisher
if (!websites.TryAdd(propertyName, value))
{
  int index1 = websites.IndexOf(propertyName); // Second lookup operation
  CUI.Warning("Element " + value + " ist bereits vorhanden!");
}

// neu
if (!websites.TryAdd(propertyName, value, out int index))
{
  CUI.Warning("Element " + value + 
              " ist bereits vorhanden an der Position " + 
              index + """!""");
}

// neu
if (websites.TryGetValue(propertyName, out string? value2, out int index2))
{
  CUI.Success($"Element {value2} wurde gefunden an der Position {index2}.");
}

JsonElement element1 = JsonSerializer.Deserialize<JsonElement>("""{ "ID" : 1, "Name" : "Dr. Holger Schwichtenberg", "Website": "www.IT-Visions.de" }""");
Console.WriteLine(element1.GetPropertyCount()); // 3

JsonElement element2 = JsonSerializer.Deserialize<JsonElement>("""[ 1, 2, 3, 4 ]""");
Console.WriteLine(element2.GetArrayLength()); // 4

System.Text.Json.Nodes.JsonArray array = JsonSerializer.Deserialize<System.Text.Json.Nodes.JsonArray>("""[ 1, 2, 3, 4, 5, 6, 7, 8, 9 ]""");
System.Console.WriteLine(array.Count); // 9
PrintJsonArray(array);

array.RemoveRange(5, 2);
PrintJsonArray(array);

array.RemoveAll(n => n.GetValue<int>() > 5);
PrintJsonArray(array);