C++ decode void pointer nicely for Matlab mex

Question

I'm trying to write a C++ mex function for Matlab that can handle multiple datatypes. Matlab gives me an mxArray*, from which I can retrieve a void* for the data, and an mxClassID telling me the datatype. So I can do something like:

void *data = mxGetData(mxarray);
switch (mxGetClassID(mxarray)) {
  case mxDOUBLE_CLASS:
    my_function(static_cast<double *>(data));
  ...

my_function is templated, so this handles different datatypes nicely. But it's still very annoying to need to have this switch for every possible my_function1, my_function2, etc.

So far, the solution I've come up with is to use a functional approach and have a method that accepts a functor:

template <typename ReturnType, typename FunctorType>
ReturnType mxarr_apply(const mxArray *inarr, FunctorType functor) {
  void *data = mxGetData(inarr);
  switch (mxGetClassID(inarr)) {
    case mxDOUBLE_CLASS:
      return (ReturnType) functor(static_cast<double *>(data));
    ...

This way I can put my logic in the functor (with operator() templated) and not have to recreate the switch over and over.

But I wonder if there is some other way? In Java I think I could just have a function that translates the mxClassID directly into a class reference that could then be used to instantiate a type flexibly at runtime, but this doesn't seem to be an option in C++.

Answer 1

You're correct. There's no way in C++ to get a class reference at runtime. You have to write the switch, at least once.