Testing list ownership, see https://discord.com/channels/389676745957310465/468902667003887646/1202630782791852084

project1.lpr

// castle-engine simple-compile project1.lpr --compiler-option=-gh --compiler-option=-gl --verbose

program project1;
uses
  SysUtils, Generics.Collections, Generics.Defaults;

type
  TComplexObj = class
    private
      FMainKey: String;
      FSetKey: String;
    public
      procedure Add(const AMainKey: String; const ASetKey: String);
	end;
  //PComplexObj = ^TComplexObj;
  TSomeList = specialize TObjectList<TComplexObj>;

procedure TComplexObj.Add(const AMainKey, ASetKey: String);
begin
  FMainKey := AMainKey;
  FSetKey := ASetKey;
end;


var
  I: Integer;
  obj: TComplexObj;
  Index: TSomeList;
  SetIndex: specialize TObjectDictionary<string, TSomeList>;
  MasterList: TSomeList;
begin
  // Masterlist owns all instances of TComplexObj
  MasterList := TSomeList.Create(true);
  // SetIndex just uses pointers to them
  SetIndex := specialize TObjectDictionary<string, TSomeList>.Create([doOwnsValues]);

  // Populate MasterList
  obj := TComplexObj.Create;
  obj.Add('abc', 'set1');
  MasterList.Add(obj);

  obj := TComplexObj.Create;
  obj.Add('abd', 'set2');
  MasterList.Add(obj);

  obj := TComplexObj.Create;
  obj.Add('abe', 'set2');
  MasterList.Add(obj);

  obj := TComplexObj.Create;
  obj.Add('abf', 'set1');
  MasterList.Add(obj);

  for I := 0 to MasterList.Count - 1 do
    begin
    obj := MasterList[I];
    if SetIndex.TryGetValue(obj.FSetKey, Index) then
      begin
        Index.Add(obj);
        Writeln('add to index for ', obj.FSetKey);
      end
     else
      begin
        Index := TSomeList.Create(false);
        Index.Add(obj);
        SetIndex.Add(obj.FSetKey, Index);
        Writeln('new index for ', obj.FSetKey);
      end;

  end;

  SetIndex.Free;
  MasterList.Free;
end.