Скачать или смотреть Using C++20 Modules to Manage Third-Party Library Dependencies

Learn how to effectively encapsulate third-party libraries in C++20 through proper use of modules while avoiding leaky abstractions.
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Managing Third-Party Library Dependencies in C++20 Modules

The introduction of C++20 modules has paved the way for more organized and encapsulated code structures. However, when it comes to incorporating third-party libraries, some questions arise about how to manage dependencies effectively. One common issue developers encounter is how to export dependencies from third-party libraries like spdlog within their own module. In this guide, we will discuss this problem and provide a clear, organized solution.

Understanding the Problem

When creating a module that encapsulates a logging library based on spdlog, you might be tempted to rely on the convenience of private implementations. However, if your logging interface utilizes type definitions from spdlog, such as spdlog::format_string_t, you’ll notice that if you don’t explicitly include -include <spdlog> in your source files (like test.cpp), your program won’t compile. This situation leads to the phenomenon known as leaky encapsulation, where the implementation details of your module are exposed and used by its clients.

In simpler terms, if your module’s interface depends on parts of an external library, users of your module will still need to include that library directly—causing your modularization to be less effective. Let’s explore how to handle this situation thoughtfully.

A Deep Dive into the Solution

Step 1: Recognizing Leaky Encapsulation

First and foremost, it’s vital to understand that when you allow your module to leak dependencies, users must both import your module and -include the external library. This means if a dependency isn't encapsulated well, your module offers no real advantage.

Step 2: Exposing Necessary Types

If your logging system requires specific types from spdlog, the most effective way to manage this dependency is not just to export types directly but to expose types that remain flexible. Here's how you can organize your log module while providing access to necessary dependencies:

Define Type Aliases: You can create your own type aliases in your module header that map to spdlog types, making it clearer for the users of your module while encapsulating underlying details.

Interface Design: Design your logging interface to accept the type definitions necessary for logging messages, allowing users of your module to understand what to expect without needing to delve into the spdlog headers.

Example Implementation

Flashback to the provided code snippets. Here’s a closer look at what adjustments we can make:

[[See Video to Reveal this Text or Code Snippet]]

In the code example above, we can’t directly export types such as spdlog::format_string_t<Args...> if we don't include <spdlog>. This is where recognizing leaky encapsulation comes into play.

Step 3: Wrap Dependencies

Instead of exposing spdlog directly, you could create classes and templates as wrappers around the spdlog functionality, ensuring your implementation is cleaner and users of your module won't need to expose spdlog directly in their code.

Create Wrappers: Building wrapper classes helps encapsulate and manage logging details without exposing spdlog's internals:

Use templates for flexibility

Define your log levels and serialize functions

Conclusion

By navigating through the concept of encapsulation and the implications of leaky abstractions in module design, you can create clean, maintainable code. Anyone utilizing your encapsulated log library must be aware that they may still need to -include third-party libraries if those details leak through your API. While C++20 modules serve as a powerful tool for organizing code, they require careful structuring, particularly when integrating external dependencies.

In summary,