Understanding the Purpose of Interface and Implementation Module Files in C++20

Описание: Discover why C++20 distinguishes between `interface` and `implementation` module files, and how it impacts your coding efficiency and organization.
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Understanding the Purpose of Interface and Implementation Module Files in C++20

C++20 introduces a refined module system that enhances the way we organize and manage our code. With these changes, you may encounter two distinct types of module files: interface and implementation. This guide will clarify the purpose of these types of module files and explain how they can improve your development workflow.

The Problem: Why Two Types of Module Files?

As you dive into module programming in C++20, you might find yourself confused about the necessity of separating module files into interface and implementation.

When exporting a function, you might say something like:

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

While it's possible to implement the function in the same module file, C++20 allows a formal distinction between files with the export module mymodule and module mymodule keywords. This brings up an important question: Wouldn't it be simpler to just use the export keyword without creating special interface files?

The Solution: Understanding Module Interfaces and Implementation Units

To grasp the benefits of having both types of module files, let’s examine how they function within the build system and why this organization is advantageous.

How the Build System Works

When the build system encounters an import MyModule; statement, it needs to find the corresponding module file. Here's a breakdown of the process:

Module Identification: If MyModule has not been built, the build system will initiate the build.

Source File Scanning: The system scans all known source files to determine which are necessary for building MyModule.

Efficient Lookup: The optimal method is to locate a single file that contains everything required to build MyModule.

This method allows for quicker scanning and pre-processing, which streamlines development.

The Interface Module

The interface module serves as the primary file that defines everything exported from the module. The advantages include:

Single Source of Truth: Only one file needs to be built for other modules to access the functionalities provided by MyModule.

Clarity in Exposure: Users of the module can easily see which entities are made available to them.

The Use of Partitions

While maintaining everything in one file is not necessarily the most efficient approach, this is where module partitions come into play. They allow you to:

Namespace Management: Keep the global namespace clean by providing namespaced partitions within a module.

Selective Inclusion: Include partitions that are specific to your module, avoiding unwanted clutter in your overall code structure.

Implementation Units: A Specialized Role

The role of implementation units is crucial:

Non-Importable: These files are part of a specific module but cannot be imported externally, making it clear their purpose is for implementation only.

Accessibility of Local Names: They have access to module-local names within the partitions, which are not exported, thus encapsulating the implementation details.

Conclusion: The Benefits of Using Both Types of Module Files

Having both interface and implementation module files in C++20 serves several key purposes:

Efficiency in Build Processes: The build system can operate more quickly by knowing exactly which files to access and build.

Organized Code Structure: It reduces namespace pollution, making the code easier to manage and understand.

Clear Separation of Concerns: Developers can maintain a clear distinction between what is exposed and how it is implemented, enhancing code maintainability.

By understanding the mechanics behind these module types, you can leverage them to write clean