These widgets can only display a single column from the underlying data
model, and it was previously hard-coded to use column 0. Now you can
use any column you like.
This macro goes at the top of every CObject-derived class like so:
class SomeClass : public CObject {
C_OBJECT(SomeClass)
public:
...
At the moment, all it does is create an override for the class_name() getter
but in the future this will be used to automatically insert member functions
into these classes.
