type
  IChild = interface;

  IParent = interface
    ['{5CF4EEDB-C8BE-4EDF-B604-F2902A08A007}']
    function GetChild: IChild;
  end;

  IChild = interface
    ['{5CF4D571-2C04-4B15-923B-E8D7D79DE4F6}']
    function GetParent: IParent;
  end;

  TParent = class(TInterfacedObject, IParent)
  strict private
    FChild: IChild;
  strict protected
    function GetChild: IChild;
  public
    constructor Create;
  end;

  TChild = class(TInterfacedObject, IChild)
  strict private
    [Weak]
    FParent: IParent;
  strict protected
    function GetParent: IParent;
  public
    constructor Create(const AParent: IParent);
  end;

{ TParent }

constructor TParent.Create;
begin
  inherited Create;
  FChild := TChild.Create(Self);
end;

function TParent.GetChild: IChild;
begin
  Result := FChild;
end;

{ TChild }

constructor TChild.Create(const AParent: IParent);
begin
  inherited Create;
  FParent := AParent;
end;

function TChild.GetParent: IParent;
begin
  Result := FParent;
end;