Quick start manual

6-18 Delphi Language Guide
Parameters
Variant open array parameters
Variant open array parameters allow you to pass an array of differently typed
expressions to a single procedure or function. To define a routine with a variant open
array parameter, specify array of const as the parameter’s type. Thus
procedure DoSomething(A: array of const);
declares a procedure called DoSomething that can operate on heterogeneous arrays.
The array of const construction is equivalent to array of TVarRec. TVarRec, declared
in the System unit, represents a record with a variant part that can hold values of
integer, Boolean, character, real, string, pointer, class, class reference, interface, and
variant types. TVarRec’s VType field indicates the type of each element in the array.
Some types are passed as pointers rather than values; in particular, long strings are
passed as Pointer and must be typecast to string. See the online Help on TVarRec for
details.
The following example uses a variant open array parameter in a function that creates
a string representation of each element passed to it and concatenates the results into a
single string. The string-handling routines called in this function are defined in
SysUtils.
function MakeStr(const Args: array of const): string;
var
I: Integer;
begin
Result := '';
for I := 0 to High(Args) do
with Args[I] do
case VType of
vtInteger: Result := Result + IntToStr(VInteger);
vtBoolean: Result := Result + BoolToStr(VBoolean);
vtChar: Result := Result + VChar;
vtExtended: Result := Result + FloatToStr(VExtended^);
vtString: Result := Result + VString^;
vtPChar: Result := Result + VPChar;
vtObject: Result := Result + VObject.ClassName;
vtClass: Result := Result + VClass.ClassName;
vtAnsiString: Result := Result + string(VAnsiString);
vtCurrency: Result := Result + CurrToStr(VCurrency^);
vtVariant: Result := Result + string(VVariant^);
vtInt64: Result := Result + IntToStr(VInt64^);
end;
end;
We can call this function using an open array constructor (see “Open array
constructors” on page 6-21). For example,
MakeStr(['test', 100, ' ', True, 3.14159, TForm])
returns the string “test100 T3.14159TForm”.