Enumeratos/Override/Forward declared class

program project1;

uses
  Classes;

type
  TFoo = class;
  TBar = class;

  TFooListEnumerator = class
  private
    FFooList: TList;
    FCurrentIndex: Integer;
  protected
    function GetCurrent: TFoo; virtual;
  public
    constructor Create(AList: TList);
    function MoveNext: boolean;
    property Current: TFoo read GetCurrent;
  end;

  { TBarListEnumerator }

  TBarListEnumerator = class(TFooListEnumerator)
  protected
    function GetCurrent: TBar; override;
    // ^-- Fails with: Error: There is no method in an ancestor class to be overridden: "TBarListEnumerator.GetCurrent:TBar;"
  public
    property Current: TBar read GetCurrent;
  end;

  { TBarList }

  TBarList = class(TList)
  public
    function GetEnumerator: TBarListEnumerator;
  end;

  TFoo = class
  public
    Val: Integer;
  end;

  TBar = class(TFoo)
  public
    Val2: Integer;
  end;

{ TFooListEnumerator }

function TFooListEnumerator.GetCurrent: TFoo;
begin
  result := TFoo(FFooList[FCurrentIndex]);
end;

constructor TFooListEnumerator.Create(AList: TList);
begin
  FFooList := AList;
  FCurrentIndex := -1;
end;

function TFooListEnumerator.MoveNext: boolean;
begin
  inc(FCurrentIndex);
  result := FCurrentIndex < FFooList.Count;
end;

{ TBarListEnumerator }

function TBarListEnumerator.GetCurrent: TBar;
begin
  result := TBar(inherited GetCurrent);
end;

{ TBarList }

function TBarList.GetEnumerator: TBarListEnumerator;
begin
  result := TBarListEnumerator.Create(Self);
end;

var
  BarList: TBarList;
  Bar: TBar;

begin
  BarList := TBarList.Create;
  BarList.Add(TFoo.Create);

  for Bar in BarList do
    Bar.Val2 := 1;

  BarList.Free;
end.