delphi-clean-code

name	Delphi Clean Code
description	Pragmatic clean code standards for Delphi — concise, direct, no over-engineering

Delphi Clean Code — Skill

CRITICAL SKILL — Be concise, direct and solution-focused.

Fundamental Principles

Principle	Rule
SRP	A function/class does ONE thing
DRY	Don't repeat code — extract and reuse
KISS	Simplest solution that works
YAGNI	Don't build what wasn't asked for
Boy Scout	Leave the code better than you found it

Naming Rules (Pascal Guide)

Element	Convention
Variables	Reveal intent: LCustomerCount not N
Methods	Verb + noun: GetCustomerById not Customer
Booleans	Question form: IsActive, HasPermission, CanEdit
Constants	SCREAMING_SNAKE: MAX_RETRY_COUNT
Fields	Prefix F: FCustomerName
Parameters	Prefix A: ACustomerName
Var. locations	Prefix L: LCustomer

Rule: If you need a comment to explain a name, rename it.

Method Rules

Rule	Description
Short	Maximum 20 lines, ideal 5-10
One Thing	Do one thing and do it well
One Level	One level of abstraction per method
Few Args	Maximum 3 arguments, prefer 0-2
No Side Effects	Don't mute inputs unexpectedly

Code Structure

Standard	Application
Guard Clauses	Early returns for edge cases
Flat > Nested	Avoid deep nesting (max 2 levels)
Composition	Small compound methods
Colocation	Related code together

Guard Clauses in Delphi

//❌ BAD — excessive nesting
procedure ProcessOrder(AOrder: TOrder);
begin
  if Assigned(AOrder) then
  begin
    if AOrder.Items.Count > 0 then
    begin
      if AOrder.IsValid then
      begin
        //real logic here
      end;
    end;
  end;
end;

//✅ BOM — guard clauses
procedure ProcessOrder(AOrder: TOrder);
begin
  if not Assigned(AOrder) then
    raise EArgumentNilException.Create('AOrder cannot be nil');
  if AOrder.Items.Count = 0 then
    raise EBusinessRuleException.Create('Order must have items');
  if not AOrder.IsValid then
    raise EValidationException.Create('Order validation failed');

  //real logic here — no nesting
end;

Anti-Patterns (DO NOT DO)

❌ Pattern	✅ Fix
Comment each line	Delete obvious comments
Method > 20 lines	Share by responsibility
Magic numbers	Named constants
with statement	Explicit local variables
Global variables	Constructor injection
Generic Catch	Specific exceptions
Logic in OnClick	Delegate to Service
God class / God unity	One class = one responsibility
Ignore Free	try/finally always

Memory Management

//✅ Temporary objects — always try/finally
LList := TStringList.Create;
try
  LList.Add('item');
  //use LList
finally
  LList.Free;
end;

//✅ Interfaces — reference counting automático
var LService: IMyService;
LService := TMyService.Create; //automatically released

//✅ Owner pattern for visual components
LButton := TButton.Create(Self); //Self frees automatically

AI Code Style

Situation	Action
User requests feature	Write directly
User reports bug	Correct, don't explain
Requirement unclear	Ask, don't assume

🔴 Before Editing (THINK FIRST!)

Question	Why
Which units use this?	They can break
What does this unit matter?	Interfaces can change
What tests cover this?	Tests may fail
Is it a shared component?	Multiple points affected

🔴 Rule: Edit the file + all dependents in the SAME task.

🔴 Self-Check (MANDATORY)

Check	Pergunta
✅ Goal achieved?	Did I do exactly what was asked?
✅ Edited files?	Have I modified everything necessary?
✅ Does the code work?	Have I tested/verified?
✅ No errors?	Compiles without warnings?
✅ Nothing forgotten?	Edge cases treated?
✅ Memory safe?	Objects released correctly?

🔴 Rule: If ANY check fails, correct it before finishing.