Delphi 2006 - routine parameter untyped

Question

It is possible to have a parameter in a routine which can be in the same time either an type, either an string? I know I can accomplish this by overloading a routine, I ask if it possible to do it in another way.

Assume that I have this type - TTest = (t1,t2,t3). I want to have a routine which accepts a parameter of type TTest, but in the same time to be a String, so I can call it myproc(t1) or myproc('blabla')

Answer 1

Even this can be easily accomplished with overloaded functions, considering it's a good exercise, based on David Hefferman's and Sertac Akyuz answers I made a small example to test both solutions. It is not perfect, it only shows both possibilities.

unit Unit4;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs;

type
  ttest = (t1,t2);
  TForm4 = class(TForm)
    procedure FormCreate(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
    function my(aVar:Variant):String;
    function MyUntype(const aVar):String;
  end;

var
  Form4: TForm4;

implementation

{$R *.dfm}

{ TForm4 }

procedure TForm4.FormCreate(Sender: TObject);
var aTestTypeVar : ttest;
    aString : String;
begin
 my(t1);
 my(t2);
 my('ssss');
//with untyped params
 aString := 'aaaa';
 MyUntype(aString);
 aTestTypeVar := t1;
 aString := IntToStr(Ord(aTestTypeVar));
 MyUntype(aString);//can not be a numeral due to delphi Help
end;

function TForm4.my(aVar: Variant): String;
begin
 showmessage(VarToStr(aVar));//shows either the string, either position in type
end;

function TForm4.MyUntype(const aVar): String;
begin
 //need to cast the parameter  
 try
  ShowMessage(pchar(aVar))
 except
  showmessage(IntToStr(Ord(ttest(aVar))));
 end;
end;

end.

Also I know that Variants are slow and must be used only needed.

Answer 2

You should use an overloaded function.

You already have the perfect solution to the problem and there is no need to look for a different way to do this. You could try with a single function that receives a Variant, but then that function will also receive anything which means that the following would also be legal:

myproc(0.5);
myproc(intf);
myproc(-666);

Using an overload allows you to maintain compile time type safety and there is absolutely no loss of generality in using an overload.