How to pass “nil” constant to the untyped parameter?

Question

is it possible to pass nil as an undeclared constant to the untyped parameter of some function? I have functions like these and I would like to pass some constant to the Data parameter to satisfy the compiler. Internally I'm deciding by the Size parameter. I know I can use Pointer instead of untyped parameter but it's much more comfortable for my case.

Now I'm getting E2250 There is no overloaded version of 'RS232_SendCommand' that can be called with these arguments

function RS232_SendCommand(const Command: Integer): Boolean; overload;
begin
  // is it possible to pass here an undeclared constant like nil in this example?
  Result := RS232_SendCommand(Command, nil, 0);
end;

function RS232_SendCommand(const Command: Integer; const Data; const Size: Integer): Boolean; overload;
begin
  ...
end;

This works, but I would be glad if I could leave the variable declaration.

function RS232_SendCommand(const Command: Integer): Boolean; overload;
var
  Nothing: Pointer;
begin
  Result := RS232_SendCommand(Command, Nothing, 0);
end;

---

Solution is to use somthing like this.

function RS232_SendCommand(const Command: Integer): Boolean; overload;
begin
  // as the best way looks for me from the accepted answer to use this
  Result := RS232_SendCommand(Command, nil^, 0);

  // or it also possible to pass an empty string constant to the untyped parameter
  // without declaring any variable
  Result := RS232_SendCommand(Command, '', 0);
end;

I'm doing this because some of my commands have a data sent after command transmission.

Thanks for the help

Answer 1

Easy:

RS232_SendCommand(Command, nil^, 0);

You just need to make sure that you don't access the Data parameter from inside RS232_SendCommand, but presumably that's what the 0 size parameter is for.

To my mind this is the best solution because it very explicitly states that you are passing something that cannot be accessed.

Answer 2

No, you can not. not that I knew of

Untyped Parameters

You can omit type specifications when declaring var, const, and out parameters. (Value parameters must be typed.) For example:

procedure TakeAnything(const C);

declares a procedure called TakeAnything that accepts a parameter of any type. When you call such a routine, you cannot pass it a numeral or untyped numeric constant.

From: Parameters (Delphi)

So, perhaps add another overloaded version without the const arg that you can call when Size = 0.