https://docwiki.embarcadero.com/CodeExamples/Sydney/en/Generics_Collections_TDictionary_(Delphi)

type
  TCity = class
    Country: String;
    Latitude: Double;
    Longitude: Double;
  end;

var
  Form20: TForm20;

implementation

{$R *.dfm}

procedure TForm20.Button1Click(Sender: TObject);
var
  Dictionary: TDictionary<String, TCity>;
  City, Value: TCity;
  Key: String;
  i: integer;
begin
  { Create the dictionary. }
  Dictionary := TDictionary<String, TCity>.Create;

  City := TCity.Create;
  City.Country := 'United Kingdom';
  City.Latitude := 51.5;
  City.Longitude := -0.17;
  Dictionary.Add('London', City);

  City := TCity.Create;
  City.Country := 'Argentina';
  { Notice the wrong coordinates }
  City.Latitude := 0;
  City.Longitude := 0;
  Dictionary.Add('Buenos Aires', City);

  { Clear all entries in the dictionary. }
  Dictionary.Clear;

  { Free the memory allocated for the dictionary. }
  Dictionary.Free;
  City.Free;
end;

end.