Return an iterator over the struct types defined in
        the module. The iterator will yield a TypeRef.

def struct_types(self):
        """
        Return an iterator over the struct types defined in
        the module. The iterator will yield a TypeRef.
        """
        it = ffi.lib.LLVMPY_ModuleTypesIter(self)
        return _TypesIterator(it, dict(module=self))