Class/Static Constants in Delphi

Question

In Delphi, I want to be able to create an private object that\'s associated with a class, and access it from all instances of that class. In Java, I\'d use:

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Answer 1

 TMyObject = class
    private
      class var FLogger : TLogLogger;
      procedure SetLogger(value:TLogLogger);
      property Logger : TLogLogger read FLogger write SetLogger;
    end;

procedure TMyObject.SetLogger(value:TLogLogger);
begin
  // sanity checks here
  FLogger := Value;
end;

Note that this class variable will be writable from any class instance, hence you can set it up somewhere else in the code, usually based on some condition (type of logger etc.).

Edit: It will also be the same in all descendants of the class. Change it in one of the children, and it changes for all descendant instances. You could also set up default instance handling.

 TMyObject = class
    private
      class var FLogger : TLogLogger;
      procedure SetLogger(value:TLogLogger);
      function GetLogger:TLogLogger;
      property Logger : TLogLogger read GetLogger write SetLogger;
    end;

function TMyObject.GetLogger:TLogLogger;
begin
  if not Assigned(FLogger)
   then FLogger := TSomeLogLoggerClass.Create;
  Result := FLogger;
end;

procedure TMyObject.SetLogger(value:TLogLogger);
begin
  // sanity checks here
  FLogger := Value;
end;