Delphi / Object Pascal

Delphi (RAD Studio) and Free Pascal (Lazarus) keep Object Pascal alive. It is famous for Single EXE deployment and instant compilation.

When to Use

• Rapid Application Development (RAD) for Windows Desktop: Building native Windows desktop applications with rich VCL graphical controls.
• Legacy Enterprise Maintenance: Modernizing and maintaining established corporate desktop software suites.
• Single-Binary Zero-Dependency Native Compilation: Producing fast, standalone native binaries that run without external runtime frameworks.
• High-Performance Database Clients: Interfacing with enterprise SQL databases via native FireDAC data access components.

Quick Start

program HelloWorld;
{$APPTYPE CONSOLE}
uses
  System.SysUtils;

begin
  try
    Writeln('Hello from Delphi Object Pascal!');
  except
    on E: Exception do
      Writeln(E.ClassName, ': ', E.Message);
  end;
end.

Core Concepts

Object Pascal Strong Typing & Class Architecture

Clean, readable object-oriented architecture with explicit interfaces:

unit OrderProcessor;

interface

type
  IOrderService = interface
    ['{8F3D1E1C-3A62-47CF-A98B-7D12A9E32049}']
    function ProcessOrder(const OrderId: Integer; const Amount: Double): Boolean;
  end;

  TOrderService = class(TInterfacedObject, IOrderService)
  public
    function ProcessOrder(const OrderId: Integer; const Amount: Double): Boolean;
  end;

implementation

function TOrderService.ProcessOrder(const OrderId: Integer; const Amount: Double): Boolean;
begin
  // Business logic execution
  Result := Amount > 0.0;
end;

end.

Visual Component Library (VCL) & FireMonkey (FMX)

• VCL: Native Windows-only components wrapping direct Win32/Win64 APIs.
• FireMonkey (FMX): Cross-platform GPU-accelerated UI framework targeting Windows, macOS, iOS, and Android.

FireDAC Unified Database Connectivity

High-performance data access layer:

var
  Query: TFDQuery;
begin
  Query := TFDQuery.Create(nil);
  try
    Query.Connection := FDConnection1;
    Query.SQL.Text := 'SELECT * FROM Customers WHERE Balance > :MinBalance';
    Query.ParamByName('MinBalance').AsCurrency := 1000.0;
    Query.Open;
    // Process records
  finally
    Query.Free;
  end;
end;

Common Patterns

Safe Memory Management with Try..Finally

Problem: Object memory leaks in non-ARC desktop platforms when exceptions occur.

Solution: Use explicit try..finally destruction blocks:

procedure ProcessCustomerList;
var
  List: TStringList;
begin
  List := TStringList.Create;
  try
    List.Add('Customer 1');
    List.Add('Customer 2');
    List.SaveToFile('customers.txt');
  finally
    List.Free;
  end;
end;

Best Practices

Do:

• Always Wrap Object Allocations in try...finally: Guarantee that .Free executes to prevent memory leaks in non-ARC Windows runtimes.
• Use FireDAC for All Database Operations: Standardize on FireDAC; deprecate legacy BDE and dbExpress components.
• Target 64-Bit Windows (Win64): Ensure new applications compile for 64-bit to utilize modern memory spaces and system libraries.
• Use Parameterized Queries: Always use ParamByName() to prevent SQL injection vulnerabilities.

Don't:

• Ignore compiler hints and warnings: Treat Delphi compiler warnings with priority; they frequently identify uninitialized variables.
• Use global variables in units: Keep state encapsulated inside classes and records.
• Block the UI thread with long database queries: Execute heavy queries asynchronously using TTask.Run from the Parallel Programming Library.

Troubleshooting

References

• Free Pascal