{
AssertErrorProc example
The following code is a self-contained unit that you can add to a project
that logs failed assertions to the event log rather than raising an
exception. If /Debug is passed to the application as a command-line
parameter, all failed Assert calls cause a call to OutputDebugString,
which sends a messages to the Event Log window if run from Delphi, or
does nothing if run outside the IDE (OutputDebugString is a no-op if not
run from within a debugger). A nice side benefit is that all the line
numbers and unit names can be stripped from the EXE by turning off
assertions and rebuilding the project.
Note: AssertErrorHandler should do as little as possible.  This routine
does no cleanup, so no variables, no compiler generated variables.
Procedure calls are OK.
Note:   This example was originally provided by Brian Long.
}
type
  TForm1 = class(TForm)
    procedure Button1Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

  TStorage = class(TObject)
    FData: string;
    property Data: string read FData write FData;
  private
    { Private declarations }
  public
    { Public declarations }
  end;

  var
  Form1: TForm1;

procedure AssertErrorHandler(const Message, Filename: string;  LineNumber: Integer; ErrorAddr: Pointer);

implementation

{$R *.dfm}

{$ASSERTIONS ON}

type
  EMyAssert = class(Exception);
  

procedure DoMessage(Message, Filename: String; LineNumber: Integer; ErrorAddr: Pointer);
var
  S: String;
begin
  S := Format('%s (%s, line %d, address $%x)',
    [Message, Filename, LineNumber, Pred(Integer(ErrorAddr))]);
  OutputDebugString(PChar(S));
end;

procedure AssertErrorHandler(const Message, Filename: string;  LineNumber: Integer; ErrorAddr: Pointer);
{ No local variables.  Not compiler generated temporary variables. }
{ Using the call stack here will cause Access Violation errors. }
begin
  DoMessage(Message, Filename, LineNumber, ErrorAddr);
  raise EMyAssert.Create('Boom!');
end;

procedure AssertErrorNoHandler(const Message, Filename: string; LineNumber: Integer; ErrorAddr: Pointer);
begin
end;

procedure ModifyStorage(AStorage: TStorage; const s: string);
begin
  Assert(AStorage <> nil, 'Value');
  AStorage.Data := s;
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
  ModifyStorage(nil, 'Oops');
end;

initialization
  if FindCmdLineSwitch('Debug', ['/', '-'], True) then
  begin
    MessageDlg('Command line switch found!', mtInformation, [mbOK], 0);
//    OldProc := System.AssertErrorProc;
    System.AssertErrorProc := @AssertErrorHandler
  end
  else
    System.AssertErrorProc := @AssertErrorNoHandler;

  ModifyStorage(nil, 'Ooops');

{
This example demonstrates how Pred and Succ can be used to
manage enumerations.
}
procedure TForm1.Button1Click(Sender: TObject);
type
  Colors = (RED,BLUE,GREEN);
var
  S: string;
begin
  S := 'The predecessor of 5 is ' + IntToStr(Pred(5)) + #13#10;
  S := S + 'The successor of 10 is ' + IntToStr(Succ(10)) + #13#10;
  if Succ(RED) = BLUE then
    S := S + 'In the type Colors, RED is the predecessor of BLUE.';
  MessageDlg(S, mtInformation, [mbOk], 0, mbOk);
end;