program Generics;

{$APPTYPE CONSOLE}

{$R *.res}

uses
  FastMM4
  , System.SysUtils
  , System.Classes
  ;

type
  TObjectCreator = class
    FObject: TObject;
    constructor Create(aObject: TObject);
    destructor Destroy; override;
  end;

  TGenObjectCreator<TC: TPersistent, constructor> = class
    FObject: TC;
    constructor Create;
    destructor Destroy; override;
  end;

{TObjectCreator}

constructor TObjectCreator.Create(aObject: TObject);
begin
  FObject := aObject;
  writeln(Format('class FObject (%s) created', [FObject.ClassName]));
end;

destructor TObjectCreator.Destroy;
begin
  if Assigned(FObject) then
    FObject.Free;
end;

{TGenObjectCreator}

constructor TGenObjectCreator<TC>.Create;
begin
  FObject := TC.Create;
  writeln(Format('class FObject (%s) created', [TC.ClassName]));
end;

destructor TGenObjectCreator<TC>.Destroy;
begin
  FObject.Free;
end;

begin
  try
    { TODO -oUser -cConsole Main : Insert code here }
  /////////////////////////////////////
  ///  typecasting avoiding with Generics
  ///
  ///  1. using classic TObject
  writeln('TObjectCreator creation ..');
  with TObjectCreator.Create(TStringList.Create) do
  try
    TStringList(FObject).Append('first'); // typecast necessary
    writeln('typecast necessary to call real object''s methods:');
    writeln(TStringList(FObject).Text);
  finally
    Free;
  end;

  ///  2. using generic TObject<TStringList>
  writeln('TGenObjectCreator creation ..');
  with TGenObjectCreator<TStringList>.Create do
  try
    FObject.Append('first');
    writeln(Format('NO typecast necessary to call %s''s methods:', [FObject.ClassName]));
    writeln(FObject.Text);
  finally
    Free;
  end;

  readln;
  except
    on E: Exception do
      Writeln(E.ClassName, ': ', E.Message);
  end;
end.