[lazarus] class-references

[Albert Zeyer]

Hello,

I want to use class-references (class of SOMECLASS) as a way for a dynamic object factory.
First I tried it with the predefined type TClass (:= class of TObject), but this doesn't work, because Create is not virtual in TObject (it costs some time to find out that this is the problem, nevertheless it is logical in some way... perhaps my experiences with ObjectPascal are to small). So I tried the following and it works as I want:

// ---------------------------------------------
...
type
  TBaseTestObject = class
    constructor Create(); virtual;
  end;

  TBaseTestClass = class of TBaseTestObject;

  TTestObject = class(TBaseTestObject)
  public
    constructor Create(); override;
    destructor Destroy(); override;
  end;


  TSkriptTestForm = class(TForm)
    Button1: TButton;
    procedure Button1Click(Sender: TObject);
    mTest: TTestObject;
  end;

procedure TSkriptTestForm.Button1Click(Sender: TObject);
var
  cls: TBaseTestClass;
begin
  cls := TTestObject;
  mTest := cls.Create() as TTestObject;
end;

constructor TBaseTestObject.Create();
begin
  // is this needed? it calls TObject.Create, but what does it?
  inherited Create();
 
  WriteLn('TBaseTestObject Create');
end;

constructor TTestObject.Create();
begin
  inherited Create();
 
  WriteLn('TTestObject Create');
end;

destructor TTestObject.Destroy();
begin
  WriteLn('TTestObject Destroy');
 
  inherited Destroy();
end;

// ---------------------------------------------     

But is there an easier way than this, so that I can use simply TClass?
I think, RTTI is very powerfull and there should be a way to do the same as above without a virtual constructor. But is it clean?

In practice, I have a abstract base class with a function like this:

function TMyBase.CreateCopy(): TMyBase;
begin
  Result := Self.ClassType.Create(); // this doesn't work because ClassType is a TClass
  // TODO: fill the result with same data ...
end;

Albert