C++ Template Classes and Matlab Mex - c++

Question

I'm wondering if there is an elegant way to write a Matlab/Mex interface to templated C++ code.
Here is the situation: say I have written a very nice set of C++ template classes like so:
template<FooType T>
Foo{
private:
//Some data
public:
//Constructors, methods
};
template<BarType S>
Bar{
private:
//Some data
public:
//Constructors, methods
};
template<FooType T, BarType S>
MyClass{
private:
Foo<T> *D;
Bar<S> *M;
public:
//Constructors, methods
};
If I have say, n different FooTypes and m different BarTypes, I have n*m different parameter choices for MyClass (FooType and BarType are custom typenames, incedentally). Now, if I was writing a C++ program to use these classes, it would look very simple:
int main()
{
Foo<fooType1> *F = new Foo<fooType1>(params);
Bar<barType3> *B = new Bar<barType3>(params);
MyClass<fooType1,barType3> *M = new MyClass(F,B);
M->doThing();
return 0;
}
I compile main.cpp and run it and rejoice. This works because I have selected template parameters at compile time, as per C++ template design. This works very well for me so far, and I like the design.
Now suppose I want to write the same type of program as main.cpp, but using Matlab as the scripting language and a Mex interface to my classes.hpp. The main reason for wanting to do this is that my code is an add-on to an exisiting matlab package. Is there an elegant way to write my mex file so that I have access to every possible pair of template parameters? What I have started to do is write my interface file with a lot of switch statements so that I can select FooType and BarType - essentially the Mex file compiles every possible (n*m) class instance and leaves them sitting there for Matlab to use. This seems OK for now (I have n=3, m=2), but it also seems sloppy and difficult to maintain.
I have thought about making the "user" re-compile the mex file every time they want to choose a different FooType and BarType, but this also seems a bit irritating (to the average Matlab user anyway). Thanks for your input!

Answer 1

I'm not familiar with Mex; I'm just a C++ user. What you describe is not possible without direct MATLAB support for run-time library generation, which I don't think is even a thing that exists. You will definitely need to pre-instantiate everything at compile time. This is not simple.
The problem, as you have said, is that the templates are all generated at compile time, and they aren't used until runtime, when all the type information is gone. The mangled names shouldn't be an issue, assuming MATLAB knows the mangling scheme.
So you'll have to solve this at the C++ level. In C++, there's no type-safe way to get the name of a type as a string. The only solution is to use macros to eliminate some of the bloat. This is unfortunate, because if it were possible, a very elegant solution would be possible with a std::tuple of all your valid parameter types, and a little recursive template magic.