，转智能指针的另外一种实现 - Smart pointers in Delphi
Strongly-typed smart pointers are now possible in Delphi, leveraging the work on generics. Here's a simple smart pointer type:
TSmartPointer<T: class> = record
strict private
FValue: T;
FLifetime: IInterface;
public
constructor Create(const AValue: T); overload;
class operator Implicit(const AValue: T): TSmartPointer<T>;
property Value: T read FValue;
end;
Here it is in action, where TLifetimeWatcher is a little class that executes some code when it dies:
procedure UseIt;
var
x: TSmartPointer<TLifetimeWatcher>;
begin
x := TLifetimeWatcher.Create(procedure
begin
Writeln('I died.');
end);
end;
Here's the full project code that defines TSmartPointer<>, TLifetimeWatcher, and the above test routine:
{$APPTYPE CONSOLE}
uses
SysUtils;
type
TLifetimeWatcher = class(TInterfacedObject)
private
FWhenDone: TProc;
public
constructor Create(const AWhenDone: TProc);
destructor Destroy; override;
end;
{ TLifetimeWatcher }
constructor TLifetimeWatcher.Create(const AWhenDone: TProc);
begin
FWhenDone := AWhenDone;
end;
destructor TLifetimeWatcher.Destroy;
begin
if Assigned(FWhenDone) then
FWhenDone;
inherited;
end;
type
TSmartPointer<T: class> = record
strict private
FValue: T;
FLifetime: IInterface;
public
constructor Create(const AValue: T); overload;
class operator Implicit(const AValue: T): TSmartPointer<T>;
property Value: T read FValue;
end;
{ TSmartPointer<T> }
constructor TSmartPointer<T>.Create(const AValue: T);
begin
FValue := AValue;
FLifetime := TLifetimeWatcher.Create(procedure
begin
AValue.Free;
end);
end;
class operator TSmartPointer<T>.Implicit(const AValue: T): TSmartPointer<T>;
begin
Result := TSmartPointer<T>.Create(AValue);
end;
procedure UseIt;
var
x: TSmartPointer<TLifetimeWatcher>;
begin
x := TLifetimeWatcher.Create(procedure
begin
Writeln('I died.');
end);
end;
begin
try
UseIt;
Readln;
except
on E:Exception do
Writeln(E.Classname, ': ', E.Message);
end;
end.
Update: Fixed capture - was capturing a location in the structure, which of course will be freely copied etc.
原帖地址： http://barrkel.blogspot.com/2008/09/smart-pointers-in-delphi.html