Handling Third-Party Libraries

Handling third-party libraries that do not use C++20 modules involves a few strategies to ensure compatibility and maintainability. Here's how you can integrate these libraries into your C++20 project effectively.

The simplest approach is to continue using traditional #include directives for third-party libraries. This method requires no modification to the libraries and ensures they work as intended. Here's an example:

1#include <iostream>
2
3// Traditional include
4#include "third_party_library.h"
5
6int main() {
7  // Function from third-party library
8  third_party_function();
9}

You can convert third-party headers into header units using the import statement. This allows you to gradually transition to modules while still using existing headers. Here's an example:

1// third_party_library.h
2#pragma once
3void third_party_function();

1// main.cpp
2// Creating a header unit
3import "third_party_library.h";
4
5int main() {
6  third_party_function();
7}

Another approach is to create a module that wraps the third-party library. This module can expose the necessary functionality while hiding the implementation details. Here's an example:

1// third_party_wrapper.cppm
2export module ThirdPartyWrapper;
3#include "third_party_library.h"
4
5export void wrapped_function() {
6  third_party_function();
7}

1// main.cpp
2import ThirdPartyWrapper;
3
4int main() {
5  wrapped_function();
6}

For headers that need to be included before the module declaration, use the global module fragment. This ensures preprocessor directives and macros are handled correctly. For example:

1module; // Global module fragment
2#include "third_party_library.h"
3
4export module MyModule;
5import <iostream>;
6
7export void myFunction() {
8  third_party_function();
9}

When integrating third-party libraries, ensure your build system correctly handles the dependencies. Use package managers or build systems like CMake to manage and configure the inclusion of these libraries.

Example: CMake Integration

Here's an example of how you might configure a CMake project to use a third-party library with modules.

1cmake_minimum_required(VERSION 3.20)
2project(MyProject)
3
4# Add third-party library
5add_library(
6  third_party_library STATIC third_party_library.cpp
7)
8
9# Create module
10add_library(MyModule STATIC my_module.cppm)
11target_link_libraries(
12  MyModule PRIVATE third_party_library
13)
14
15# Set target properties
16set_target_properties(MyModule PROPERTIES
17  CXX_STANDARD 20
18  CXX_STANDARD_REQUIRED YES
19  CXX_EXTENSIONS NO
20)
21
22# Main executable
23add_executable(MyApp main.cpp)
24target_link_libraries(MyApp PRIVATE MyModule)

Integrating third-party libraries that do not use C++20 modules can be done using traditional #include directives, creating header units, or wrapping them in modules.

Each method has its benefits and can be chosen based on the specific needs and constraints of your project.