refactoring

Delphi Code Refactoring — Rules

Use these rules when detecting or fixing code smells in Object Pascal. Refactoring doesn't change behavior — it just improves the internal structure.

🔴 Code Smells that Require Immediate Refactoring

✂️ Extract Method

Extract purposeful blocks of code into named methods.

//❌ BEFORE — long method without separation of responsibilities
procedure TOrderService.PlaceOrder(AOrder: TOrder);
var
  LTotal: Currency;
  LDiscount: Currency;
  LItem: TOrderItem;
begin
  // Calcula total
  LTotal := 0;
  for LItem in AOrder.Items do
    LTotal := LTotal + (LItem.UnitPrice * LItem.Quantity);

  //Apply discount
  if AOrder.Customer.IsVip then
    LDiscount := LTotal * 0.10
  else if LTotal > 500 then
    LDiscount := LTotal * 0.05
  else
    LDiscount := 0;

  LTotal := LTotal - LDiscount;

  //Validates stock
  for LItem in AOrder.Items do
  begin
    if LItem.Quantity > LItem.Product.StockQty then
      raise EInvalidOrderException.CreateFmt(
        'Estoque insuficiente: %s', [LItem.Product.Name]);
  end;

  AOrder.TotalAmount := LTotal;
  FRepository.Save(AOrder);
end;

//✅ AFTER — each responsibility in its own method
procedure TOrderService.PlaceOrder(AOrder: TOrder);
begin
  ValidateStock(AOrder);
  AOrder.TotalAmount := CalculateTotalWithDiscount(AOrder);
  FRepository.Save(AOrder);
end;

function TOrderService.CalculateSubtotal(AOrder: TOrder): Currency;
var LItem: TOrderItem;
begin
  Result := 0;
  for LItem in AOrder.Items do
    Result := Result + (LItem.UnitPrice * LItem.Quantity);
end;

function TOrderService.CalculateDiscount(AOrder: TOrder; ASubtotal: Currency): Currency;
const
  VIP_DISCOUNT_RATE     = 0.10;
  BULK_DISCOUNT_RATE    = 0.05;
  BULK_DISCOUNT_MINIMUM = 500;
begin
  if AOrder.Customer.IsVip then
    Result := ASubtotal * VIP_DISCOUNT_RATE
  else if ASubtotal > BULK_DISCOUNT_MINIMUM then
    Result := ASubtotal * BULK_DISCOUNT_RATE
  else
    Result := 0;
end;

function TOrderService.CalculateTotalWithDiscount(AOrder: TOrder): Currency;
var LSubtotal: Currency;
begin
  LSubtotal := CalculateSubtotal(AOrder);
  Result := LSubtotal - CalculateDiscount(AOrder, LSubtotal);
end;

procedure TOrderService.ValidateStock(AOrder: TOrder);
var LItem: TOrderItem;
begin
  for LItem in AOrder.Items do
    if LItem.Quantity > LItem.Product.StockQty then
      raise EInvalidOrderException.CreateFmt(
        'Estoque insuficiente: %s', [LItem.Product.Name]);
end;