TMyAbstractList = class
private
  FList: TList;
  FSize: Integer;
protected
  property Size: Integer read FSize;
protected
  procedure Get(AIdx, out AVal);
  procedure Set(AIdx, const AVal);
  procedure CopyData(const AFrom; out ATo); virtual; abstract;
  procedure FinalizeData(var AData); virtual; abstract;
public
  constructor Create(ASize: Integer);
  destructor Destroy; override;
  procedure Add(const AData);
  procedure Delete(AIdx: Integer);
  procedure Clear;
end;

TMyFixedList = class(TMyAbstractList)
protected
  procedure CopyData(const AFrom; out ATo); override;
  procedure FinalizeData(var AData); override;
end;

{ TMyAbstractList }

constructor TMyAbstractList.Create(ASize: Integer);
begin
  inherited Create;
  FList := TList.Create;
  FSize := ASize;
end;

destructor TMyAbstractList.Destroy; 
begin
  Clear;
  FList.Free;
  inherited Destroy;
end;

procedure TMyAbstractList.Get(AIdx, out AVal);
begin
  CopyData(FList[AIdx]^, AVal);
end;

procedure TMyAbstractList.Set(AIdx, const AVal);
begin
  CopyData(AVal, FList[AIdx]^);
end;

procedure TMyAbstractList.Add(const AData);
var
  LPtr: Pointer;
begin
  GetMem(LPtr, FSize);
  FillChar(LPtr, FSize, 0);
  CopyData(AVal, LPtr^);
  FList.Add(LPtr);
end;

procedure TMyAbstractList.Delete(AIdx: Integer);
var
  LPtr: Pointer;
begin
  LPtr := FList[AIdx];
  FinalizeData(LPtr^);
  FreeMem(LPtr);
  FList.Delete(AIdx);
end;

procedure TMyAbstractList.Clear;
var
  Li: Integer;
begin
  for Li := FList.Count - 1 downto 0 d0
    Delete(Li);
end;

{ TMyFixedList }

procedure TMyFixedList.CopyData(const AFrom; out ATo); 
begin
  Move(AFrom, ATo, Size);
end;

procedure TMyFixedList.FinalizeData(var AData); override;
begin
  // not need finalize
end;