Across multiple modules

When developing larger projects, you may need to create multiple C++ Python extension modules that communicate with each other. For example, module B might need to use a class defined and wrapped in module A.

clair-c2py generates up to two files for each wrapped module:

A .wrap.cxx file (the implementation of the bindings), always generated.
A .wrap.hxx file (a small header declaring which classes are wrapped in A), generated only if module A wraps at least one class.

The .wrap.hxx file allows other modules to know the type wrapped in module A. Technically, it just specializes of the c2py::is_wrapped<T> variable for each type T wrapped in module A. Modules that wrap only free functions and/or enums do not produce a .wrap.hxx, since there is no per-class information to share.

Example: Two communicating modules

Module A: Defining a class

Let’s create the first module that wraps a class N::A:

my_class.hpp:

namespace N {
  struct A {
    int k = 5;
    int f(int i) { return i + k; }
  };
}

module_a.cpp:

#include <c2py/c2py.hpp>
#include "./my_class.hpp"

#include "module_a.wrap.cxx"

clair-c2py generates module_a.wrap.cxx and module_a.wrap.hxx.

Module B

Now create a second module that uses the wrapped class A from module A:

module_b.cpp:

#include <c2py/c2py.hpp>
#include "./my_class.hpp"
#include "./module_a.wrap.hxx"  // declares that N::A is wrapped

struct B {
  int g(int i, N::A const &a) { return i + a.k; }
};

#include "module_b.wrap.cxx"

CMake configuration

In your CMakeLists.txt, ensure module A is compiled before module B:

# Add both modules
# FIXME
add_clair_module(module_a)
add_clair_module(module_b)

# Module B depends on module A's .wrap.hxx file
add_dependencies(module_b module_a)

Usage in Python

Once both modules are compiled, you can use them together:

import module_a
import module_b

# Create objects from both modules
a = module_a.A()
b = module_b.B()

# Use them together - B.g() takes an A object
result = b.g(2, a)  # Returns 7 (2 + a.k where a.k = 5)