Delphi Language Guide Delphi for Microsoft Win32 Delphi for the Microsoft. Net framework

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
124

---

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.
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. For example,
MakeStr(['test', 100, ' ', True, 3.14159, TForm])
returns the string 
'test100 T3.14159TForm'
.