So, once again I am learning new things and I came across Smart Pointers. I had code
procedure TForm3.BitBtn1Click(Sender: TObject);
var
_StringList: ISmartPointer<TStringList>;
begin
_StringList := TSmartPointer<TStringList>.Create(TStringList.Create);
end;
As you see variable declaration is kinda odd, and simplification is needed. I came across another solution
procedure TForm3.btnDelphiClick(Sender: TObject);
var
_StringList: TStringList;
begin
_StringList := SmartGuard.SmartGuard<TStringList>(TStringList.Create(False));
end;
Sadly, it does not work with parameterless constructor
procedure TForm3.btnDelphiClick(Sender: TObject);
var
_StringList: TStringList;
begin
_StringList := SmartGuard.SmartGuard<TStringList>(TStringList.Create);
end;
[dcc32 Error] Main.pas(47): E2089 Invalid typecast
Am I out of luck here? P.S. I know some of you would argue I should stick to try..finally block, but this is out of curiosity.
unit SmartGuard;
interface
type
IGuard = interface
['{CE522D5D-41DE-4C6F-BC84-912C2AEF66B3}']
end;
TGuard = class(TInterfacedObject, IGuard)
private
FObject: TObject;
public
constructor Create(AObject: TObject);
destructor Destroy; override;
end;
SmartGuard<T: class> = record
private
FGuard: IGuard;
FGuardedObject: T;
public
class operator Implicit(GuardedObject: T): SmartGuard<T>;
class operator Implicit(Guard: SmartGuard<T>): T;
end;
implementation
uses
{Delphi}
System.SysUtils
{Project}
;
constructor TGuard.Create(AObject: TObject);
begin
FObject := AObject;
end;
destructor TGuard.Destroy;
begin
FObject.Free;
inherited;
end;
{ SmartGuard }
class operator SmartGuard<T>.Implicit(GuardedObject: T): SmartGuard<T>;
begin
Result.FGuard := TGuard.Create(GuardedObject);
Result.FGuardedObject := GuardedObject;
end;
class operator SmartGuard<T>.Implicit(Guard: SmartGuard<T>): T;
begin
Result := Guard.FGuardedObject;
end;
end.
I would love to find a solution that would not require additional "method" calling as in here https://github.com/marcocantu/DelphiSessions/blob/master/DelphiLanguageCodeRage2018/02_SmartPointers/SmartPointerClass.pas e.g. _StringList.Value.Add('foo');
and "special" brackets e.g. _StringList := TSmartPointer<TStringList>.Create(TStringList.Create)();
The compiler needs help disambiguating
TStringList.Create
The compiler doesn't know whether this is a reference to a method, or a call to the method.
Disambiguate by adding parens to indicate that it is a call.
_StringList := SmartGuard.SmartGuard<TStringList>(TStringList.Create());