Type Verification

Rice is very picky about types - it will throw an exception on startup if it comes across a type that has not been defined. Hopefully this will not come as a surprise to most C++ developers.

For example, let’s look at the following contrived example:

class MyClass
{
};

using Fancy_T = std::vector<std::unique_ptr<std::pair<std::string, MyClass>>>

class Factory
{
  Fancy_T& make_fancy_type();
};

void setupRice()
{
  define_class<Factory>("Factory").
    define_method("make_fancy_type", &Factory::make_fancy_type);
}

When Ruby loads the Rice extension above it will throw an exception. The reason is that MyClass has not yet been defined to Rice.

When define_method is called, Rice will see that the return type for &Factory::make_fancy_type is Fancy_T. It will then drill down through the vector to the unique_ptr to the pair to MyClass. When it encounters MyClass it will check its internal TypeRegistry and realize it has not yet been defined and throw a std::runtime_exception.

To fix this requires first definining MyClass like this:

void setupRice()
{
  define_class<MyClass>("MyClass");

  define_class<Factory>("Factory").
    define_method("make_fancy_type", &Factory::make_fancy_type);
}