# What does vtkTypeMacro() do???
**URL:** https://discourse.vtk.org/t/what-does-vtktypemacro-do/14406
**Category:** Support
**Tags:** code
**Created:** [August 13, 2024, 4:27pm UTC](https://discourse.vtk.org/t/what-does-vtktypemacro-do/14406 "2024-08-13T16:27:48Z")
**Posts on this page:** 5
**Page:** 1
### Author:  [@Tomasso](https://discourse.vtk.org/u/Tomasso)
#### Post date: [August 13, 2024, 4:27pm UTC](https://discourse.vtk.org/t/what-does-vtktypemacro-do/14406/1 "2024-08-13T16:27:48Z")
In summary, what does vtkTypeMacro() do?
[I see its definition here](https://vtk.org/doc/release/4.0/html/vtkSetGet_8h-source.html#l00549), but frankly don’t understand what the heck it is doing.
E.g. in this example - what is going on with struct Data?
```auto
class MyClass {
struct Data : vtkObject
{
static Data* New(); // Pointer referencing itself?
vtkTypeMacro(Data, vtkObject); // ???
};
};
```
Thanks!
---
### Author:  [@Jens\_Munk\_Hansen](https://discourse.vtk.org/u/Jens_Munk_Hansen)
#### Post date: [August 13, 2024, 6:38pm UTC](https://discourse.vtk.org/t/what-does-vtktypemacro-do/14406/2 "2024-08-13T18:38:40Z")
Just look in the header `vtkSetGet.h` in `Common/Core`.
---
### Author:  [@danlipsa](https://discourse.vtk.org/u/danlipsa)
#### Post date: [August 13, 2024, 6:46pm UTC](https://discourse.vtk.org/t/what-does-vtktypemacro-do/14406/3 "2024-08-13T18:46:05Z")
It adds Runtime Type Information (RTTI) to the VTK objects - VTK preceded the addition of this feature in C++.
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### Author:  [@Tomasso](https://discourse.vtk.org/u/Tomasso)
#### Post date: [August 13, 2024, 6:48pm UTC](https://discourse.vtk.org/t/what-does-vtktypemacro-do/14406/4 "2024-08-13T18:48:38Z")
Yes, that macro definition is what I don’t understand. Can you summarize please?
---
### Author:  [@Jens\_Munk\_Hansen](https://discourse.vtk.org/u/Jens_Munk_Hansen)
#### Post date: [August 13, 2024, 6:53pm UTC](https://discourse.vtk.org/t/what-does-vtktypemacro-do/14406/5 "2024-08-13T18:53:36Z")
It establishes the hierarchy to the parent class and defines the factory for construction of the object. This goes hand-in-hand with the `vtkStandardNewMacro(MyClass)`, you need to place in the `.cxx` file. This hierarchy is central to VTK, e.g. by inheriting from `vtkObject`, you can add observers to objects, where a weak pointer is automatically created from the callee back to the caller. I can recommend that you just expand the macro pairs used in a `.h` and a `.cxx` to see what they expand to.