Create functions that can accept variable number of parameters such as Format()

Problem/Question/Abstract:

How to create functions that can accept variable number of parameters such as Format()

Answer:

Sometimes it's necessary to pass undefined number of [different type] variables to a function -- look at Format() function in Delphi and *printf() functions in  C/C++ for example. Once you analyze the following code, you'll be on your way to creating mysterious variable parameter functions...

// FunctionWithVarArgs()
//
// skeleton for a function that
// can accept vairable number of
// multi-type variables
//
// here are some examples on how
// to call this function:
//
// FunctionWithVarArgs(
//   [ 1, True, 3, '5', '0' ] );
//
// FunctionWithVarArgs(
//   [ 'one', 5 ] );
//
// FunctionWithVarArgs( [] );
//

procedure FunctionWithVarArgs(
  const ArgsList: array of const);
var
  ArgsListTyped:
  array[0..$FFF0 div SizeOf(TVarRec)]
    of TVarRec absolute ArgsList;
  n: integer;
begin
  for n := Low(ArgsList) to
    High(ArgsList) do
  begin
    with ArgsListTyped[n] do
    begin
      case VType of
        vtInteger:
          begin
            {handle VInteger here}
          end;
        vtBoolean:
          begin
            {handle VBoolean here}
          end;
        vtChar:
          begin
            {handle VChar here}
          end;
        vtExtended:
          begin
            {handle VExtended here}
          end;
        vtString:
          begin
            {handle VString here}
          end;
        vtPointer:
          begin
            {handle VPointer here}
          end;
        vtPChar:
          begin
            {handle VPChar here}
          end;
        vtObject:
          begin
            {handle VObject here}
          end;
        vtClass:
          begin
            {handle VClass here}
          end;
        vtWideChar:
          begin
            {handle VWideChar here}
          end;
        vtPWideChar:
          begin
            {handle VPWideChar here}
          end;
        vtAnsiString:
          begin
            {handle VAnsiString here}
          end;
        vtCurrency:
          begin
            {handle VCurrency here}
          end;
        vtVariant:
          begin
            {handle VVariant here}
          end;
      else
        begin
          {handle unknown type here}
        end;
      end;
    end;
  end;
end;

//
// example function created using
// the above skeleton
//
// AddNumbers() will return the
// sum of all the integers passed
// to it
//
// AddNumbers( [1, 2, 3] )
//   will return 6
//
//

function AddNumbers(
  const ArgsList: array of const)
  : integer;
var
  ArgsListTyped:
  array[0..$FFF0 div SizeOf(TVarRec)]
    of TVarRec absolute ArgsList;
  n: integer;
begin
  Result := 0;
  for n := Low(ArgsList) to
    High(ArgsList) do
  begin
    with ArgsListTyped[n] do
    begin
      case VType of
        vtInteger: Result := Result + VInteger;
      end;
    end;
  end;
end;