1. type
2.   IWidget = interface(IInvokable)
3.     function GetId: string;
4.     function WidgetType: string;
5.  
6.     property Id: string read GetId;
7.   end;
8.  
9.   TWidget = class(TInterfacedObject, IWidget)
10.   private
11.     FId: string;
12.     function GetId: string;
13.   public
14.     constructor Create(const Id: string);
15.     function WidgetType: string; virtual; abstract;
16.  
17.     property Id: string read GetId;
18.   end;
19.  
20.   TRoundWidget = class(TWidget)
21.   private
22.     FRadius: double;
23.   public
24.     constructor Create(const Id: string; const Radius: double);
25.     function WidgetType: string; override;
26.  
27.     property Radius: double read FRadius;
28.   end;
29.  
30. { TWidget }
31.  
32. constructor TWidget.Create(const Id: string);
33. begin
34.   inherited Create;
35.  
36.   FId := Id;
37. end;
38.  
39. function TWidget.GetId: string;
40. begin
41.   result := FId;
42. end;
43.  
44. { TRoundWidget }
45.  
46. constructor TRoundWidget.Create(const Id: string; const Radius: double);
47. begin
48.   inherited Create(Id);
49.  
50.   FRadius := Radius;
51. end;
52.  
53. function TRoundWidget.WidgetType: string;
54. begin
55.   result := 'Round';
56. end;
57.  
58.  
59. var
60.   widget: TWidget;
61.   iw: IWidget;
62.   f: RIFunc<string>; // type RIFunc<R> = reference to function(const Instance): R;
63.   r: RIFunc<double>;
64.   id, wt: string;
65.   rad: double;
66. begin
67.   widget := TRoundWidget.Create('42', 42);
68.  
69.   try
70.     f := RIConstructor<TWidget>.PropGetter<string>('Id');
71.     id := f(widget);
72.     WriteLn(id);  // 42
73.  
74.     r := RIConstructor<TRoundWidget>.PropGetter<double>('Radius');
75.     rad := r(widget);
76.     WriteLn(rad); // 4.20000000000000E+0001
77.  
78.     f := RIConstructor.Func<string>(TypeInfo(TWidget), 'WidgetType');
79.     wt := f(widget);
80.     WriteLn(wt);  // Round
81.  
82.  
83.     iw := TRoundWidget.Create('abc', 123);
84.  
85.     f := RIConstructor.PropGetter<string>(TypeInfo(IWidget), 'Id');
86.     id := f(iw);  
87.     WriteLn(id);  // abc
88.    
89.   finally
90.     widget.Free;
91.   end;
92. end.