You can write a parser for an IDL, but you can’t reasonably write a parser for C++. So you have to move the definition of whatever types of methods or fields you want to reflect on into the IDL, instead of defining them natively in C++. (Or worse, have separate definitions in both the IDL and C++.) Which tends to be cumbersome – especially if you want to define a lot of generic types (since then the code generator can’t statically determine the full list of types). It can work, but there’s a reason I rarely see anyone using this approach.