Delphi in a Nutshell

Name

TClass Type

Syntax

type TClass = class of TObject;

Description

TClass is the root metaclass type. You can use TClass any time you need a generic class reference.

Tips and Tricks

• You can call any class method by invoking the method from a class reference.

• You cannot use the is and as operators on a class reference, but you can call the InheritsFrom class method to test whether a class reference inherits from another class.

• Delphi represents a class reference as a pointer to the class’s VMT. Thus, the size of a TClass reference is the same size as a Pointer.

Example

// Map class names to class references.
type
  TClassMap = class
  private
    fList: TStrings;
    function GetClass(const Name: string): TClass;
    procedure PutClass(const Name: string; Value: TClass);
  public
    procedure Add(ClsRef: TClass);
    property Classes[const Name: string]: TClass
        read GetClass write SetClass; default; end; procedure TClassMap.Add(ClsRef: TClass); begin // TStrings takes TObject as the associated data, // so cast TClass to TObject. fList.AddObject(ClsRef.ClassName, TObject(ClsRef)); end; function TClassMap.GetClass(const Name: string): TClass; begin Result := TClass(fList.Objects[fList.IndexOf(Name)]); end; procedure TClassMap.SetClass(const Name: string; Value: TClass); var Index: Integer; begin Index := fList.IndexOf(Name); if Index < 0 then fList.AddObject(Name, TObject(Value)) else fList.Objects[Index] := TObject(Value); end; ... var Map: TClassMap; Cls: TClass; ... Map.Add(TObject); Map.Add(TComponent); ...