Title: How to implement a Smart Pointer Class C almost
unit Unit2;
interface
uses
Classes;
type
TSmartPointer = class(TComponent)
private
FPointer: Pointer;
FReadOnly: Boolean;
FOwnsMemory: Boolean;
function GetIsNil: Boolean;
procedure SetPointer(const Value: Pointer);
public
constructor Create(AOwner: TComponent); overload; override;
constructor Create(AOwner: TComponent; APointer: Pointer; AOwnsMemory: Boolean = True);
overload;
destructor Destroy; override;
property Memory: Pointer read FPointer write SetPointer;
property OwnsMemory: Boolean read FOwnsMemory write FOwnsMemory;
property IsReadOnly: Boolean read FReadOnly write FReadOnly;
property IsNil: Boolean read GetIsNil;
procedure FreeMemory;
function AssignMemory(APointer: Pointer): Boolean;
end;
implementation
{ TSmartPointer }
function TSmartPointer.AssignMemory(APointer: Pointer): Boolean;
begin
Result := False;
if not FReadOnly then
begin
FPointer := APointer;
Result := (FPointer = APointer);
end;
end;
constructor TSmartPointer.Create(AOwner: TComponent);
begin
inherited;
FOwnsMemory := True;
FPointer := nil;
FReadOnly := False;
end;
constructor TSmartPointer.Create(AOwner: TComponent; APointer: Pointer;
AOwnsMemory: Boolean);
begin
inherited Create(AOwner);
FOwnsMemory := AOwnsMemory;
FPointer := APointer;
FReadOnly := False;
end;
destructor TSmartPointer.Destroy;
begin
if FOwnsMemory = True then Dispose(FPointer);
FPointer := nil;
inherited;
end;
procedure TSmartPointer.FreeMemory;
begin
Dispose(FPointer);
FPointer := nil;
end;
function TSmartPointer.GetIsNil: Boolean;
begin
Result := (FPointer = nil);
end;
procedure TSmartPointer.SetPointer(const Value: Pointer);
begin
if not FReadOnly then FPointer := Value;
end;
end.
(*-------------------------------------------------------------------
Here is a sample form to see its usage:
--------------------------------------------------------------------*)
unit Unit1;
interface
uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs, Unit2, StdCtrls;
type
TForm1 = class(TForm)
Button1: TButton;
procedure FormCreate(Sender: TObject);
procedure Button1Click(Sender: TObject);
private
{ Private declarations }
public
{ Public declarations }
end;
var
Form1: TForm1;
ATextPointer: TSmartPointer;
implementation
{$R *.dfm}
procedure TForm1.FormCreate(Sender: TObject);
var
A: ^String;
begin
New(A);
ATextPointer := TSmartPointer.Create(Form1, A, True);
string(ATextPointer.Memory^) := 'a pascal smart pointer stored this text!';
Self.Caption := string(ATextPointer.Memory^);
end;
procedure TForm1.Button1Click(Sender: TObject);
var
APointer: TSmartPointer;
ACanvas: TCanvas;
begin
ACanvas := TCanvas.Create;
APointer := TSmartPointer.Create(Form1, @ACanvas, False);
with TCanvas(APointer.Memory^) do
begin
Handle := GetWindowDC(Form1.Handle);
Brush.Color := clMoneyGreen;
FillRect(Rect(0, 0, Form1.Width, 23));
Font.Size := 10;
Font.Color := clGreen;
Font.Style := [fsBold];
TextOut((Form1.Width div 2) - (TextWidth(string(ATextPointer.Memory^)) div 2),
3, string(ATextPointer.Memory^));
end;
end;
end.