refactoring.md

Refactoring for Service

• Separate the UI from the code that you need
  • Prefer to move code to a new unit
  • Change UI errors to exceptions or use a parameter for errors

function CalculateSomething: Currency;
begin
  Result := 0;
  if not Someglobal.IsValid then
  begin
    ShowMessage('Not valid');
    Exit;
  end;
  // ... etc
end;

---

Error handling dos

function CalculateSomething: Currency;
begin
  Result := 0;
  if not Someglobal.IsValid then
    raise MyException.Create('Not valid');

  // ... etc
end;

or

function TryCalculateSomething(var OutResult: Currency; var ErrorTxt: string): Boolean;
begin
  Result := False;
  if not Someglobal.IsValid then
  begin
    ErrorTxt := ErrorTxt + 'Not valid'#10;
    Exit;
  end;

  OutResult := 42;
  Result := True;
end;

---

Error handling donts

• Don't use global-state

var
  LastErrorCode: Integer = 0;
  LastErrorText: string = '';

function CalculateSomething: Currency;
begin
  Result := 0;
  if not Someglobal.IsValid then
  begin
    LastErrorCode := 6;
    LastErrorText := 'Not valid';
    Exit;
  end;

  // ... etc
end;

---

Refactoring for Service

• Separate the UI from the code that you need
  • Prefer to move code to a new unit
  • Change UI errors to exceptions or use a parameter for errors
  • Don't use a global error state
• Try to keep Windows specific calls in separate functions or (interfaced) classes
  • {$ifdef API}
• But don't ifdef your dpr uses, Delphi will make a mess of things