// Q: How to convert callback types in the most simple way?
// A: (Bradley) I see three ways to do this: The issue is that we have a C++ callback function, and we want to pass it to a C function.
// The fastest way is wrong: You cannot just pass the C++ function pointer since you cannot mix function pointers to C and C++.
// The "right" way is to declare an "extern C" function and do all the conversions. Create a Dbt from a DBT, and then call the C function. For returned data we would have do something too. But it turns out that DBT and Dbt pointers are interchangable so that leads to
// The "fast" way. Declare an "extern C" function, and then use Dbt::get_const_Dbt() to do the conversion quickly.