Delphi in a Nutshell

Name

TVarRec Type

Syntax

type
  TVarRec = record
    case Byte of
      vtInteger:    (VInteger: Integer; VType: Byte);
      vtBoolean:    (VBoolean: Boolean);
      vtChar:       (VChar: Char);
      vtExtended:   (VExtended: PExtended);
      vtString:     (VString: PShortString);
      vtPointer:    (VPointer: Pointer);
      vtPChar:      (VPChar: PChar);
      vtObject:     (VObject: TObject);
      vtClass:      (VClass: TClass);
      vtWideChar:   (VWideChar: WideChar);
      vtPWideChar:  (VPWideChar: PWideChar);
      vtAnsiString: (VAnsiString: Pointer);
      vtCurrency:   (VCurrency: PCurrency);
      vtVariant:    (VVariant: PVariant);
      vtInterface:  (VInterface: Pointer);
      vtWideString: (VWideString: Pointer);
      vtInt64:      (VInt64: PInt64);
  end;

Description

A subroutine parameter of type array of const is actually an array of TVarRec records. Delphi converts each open array element to a TVarRec record, filling in the VType member with the type code and the appropriate member with the actual value.

Tips and Tricks

• Delphi uses open arrays and TVarRec values to implement subroutines that take a variable number of arguments, while preserving complete type safety.

• TVarRec and TVarData are entirely unrelated. They look similar because they do similar things, but they are not interchangeable.

• TVarRec can handle more types than a Variant, but it cannot handle all Delphi types. In particular, arrays, records, and enumerations are not supported.

Example

// Compute the sum of an arbitrary number of values. function Sum(const Data: array of const): Double; var I: Integer; begin Result := 0.0; for I := Low(Data) to High(Data) ...