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

[bholas]

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;

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