type
  TFontHelper = class helper for TFont
  private
    function GetBold: Boolean;
    procedure SetBold(Value: Boolean);
    function GetItalic: Boolean;
    procedure SetItalic(Value: Boolean);
    function GetUnderline: Boolean;
    procedure SetUnderline(Value: Boolean);
    function GetStrikeOut: Boolean;
    procedure SetStrikeOut(Value: Boolean);
  public
    property Bold: Boolean read GetBold write SetBold;
    property Italic: Boolean read GetItalic write SetItalic;
    property Underline: Boolean read GetUnderline write SetUnderline;
    property StrikeOut: Boolean read GetStrikeOut write SetStrikeOut;
  end;

implementation

{ TFontHelper }

function TFontHelper.GetBold: Boolean;
begin
  Result := fsBold in Style;
end;

procedure TFontHelper.SetBold(Value: Boolean);
begin
  if Value then
    Style := Style + [fsBold]
  else
    Style := Style - [fsBold];
end;

function TFontHelper.GetItalic: Boolean;
begin
  Result := fsItalic in Style;
end;

procedure TFontHelper.SetItalic(Value: Boolean);
begin
  if Value then
    Style := Style + [fsItalic]
  else
    Style := Style - [fsItalic];
end;

function TFontHelper.GetUnderline: Boolean;
begin
  Result := fsUnderline in Style;
end;

procedure TFontHelper.SetUnderline(Value: Boolean);
begin
  if Value then
    Style := Style + [fsUnderline]
  else
    Style := Style - [fsUnderline];
end;

function TFontHelper.GetStrikeOut: Boolean;
begin
  Result := fsStrikeOut in Style;
end;

procedure TFontHelper.SetStrikeOut(Value: Boolean);
begin
  if Value then
    Style := Style + [fsStrikeOut]
  else
    Style := Style - [fsStrikeOut];
end;