Delphi Style Guide EN.md

Delphi Style Guide

Version 2.1, updated 2025-10-08

This comprehensive style guide establishes conventions for modern Delphi projects across formatting, naming, structure, and coding practices.

Key Formatting Rules

Indentation & Line Length:

• Use 2 spaces per logical block (avoid tabs)
• Maximum 120 characters per line
• begin..end statements on separate lines

Comments:

• // for single-line comments
• {} for multi-line comments
• (* *) for temporarily disabled code
• /// for XML documentation

Naming Conventions Summary

Element	Convention	Example
Variables (local)	L prefix + PascalCase	LCustomerName
Variables (field)	F prefix + PascalCase	FConnectionString
Parameters	A prefix + PascalCase	AValue
Loop counters	lowercase, no prefix	i, j (exception to rules)
Constants	c prefix; sc for strings	cMaxRetries, scErrorMsg
Types/Classes	T prefix + PascalCase	TCustomer
Interfaces	I prefix + PascalCase	ILogger
Exceptions	E prefix + PascalCase	EFileNotFound
Methods	Verb + PascalCase	SaveDocument, IsValidEmail

Unit Organization

Namespace Hierarchy with Dot Notation:

• Forms: Main.Form → file Main.Form.pas → class TFormMain
• Data Modules: Main.DM → file Main.DM.pas → class TDMMain
• Nested: Customer.Details.Form → TFormCustomerDetails

Error Handling Best Practices

Always use FreeAndNil() instead of .Free:

try
  LObject := TObject.Create;
finally
  FreeAndNil(LObject);
end;

Modern Delphi Features

• Collections: Use TArray<T> for fixed sizes, TList<T> for dynamic lists, TObjectList<T> for owned objects
• Inline variables (Delphi 10.3+) preferred in loops
• Sealed classes for utility functions
• Generics for type-safe collections
• Anonymous methods for callbacks

Documentation

Use XML documentation comments with ///:

/// <summary>
/// Calculates the sum of two numbers
/// </summary>

This guide emphasizes consistency, maintainability, and modern Delphi practices.