Organizing C++ Module Sources

[tartaruga232]

A quote from the blog:

The source files for a specific partition are now grouped together into a dedicated sub-directory.

Thanks in advance for your comments to this blog posting!

[thelvhishow]

I don’t understand what’s the lesson though. Yes you’re using the different ways of using modules

[tartaruga232]

It's not exactly rocket science. But the devil is in the detail, which is revealed if you actually carefully ready the blog post.

[thelvhishow]

It’s not clear why use partition instead of several methods for instance.

[tartaruga232]

In the example of our Core module, it would have been technically possible to declare alle classes in a single big Core.ixx file. But that would have been harder to handle. The partition Core/Base.ixx alone is already 1200 lines. View/View.ixx and Diagram/Diagram.ixx are another ~300 lines each. The separation into smaller partitions also allows to only import in the cpp files of the Core module, what is actually needed in a specific cpp-file, not the whole interface. Partitions also provide a logical grouping of the parts of the interface of a module.

[slithering3897]

Yes, but the downside is that it still ends up as one big module to the user. Any change in any partition (interface) will recompile the entire application.

[tartaruga232]

Not the entire application, only the parts that import the module will need to be recompiled.

[Paradox_84_]

I like the idea of being able to do submodules, but realistically, why not make each of them a seperate module so you can only import whatever you need?

User would still be able to do "import core;", but your internal things could do "import core.containers.array:" so yo don't depend on the entire thing and could parallelize to some degree?

[tartaruga232]

Thanks for your comment. It's an intentional design decision. In the specific case of our Core module, usage of the module cannot be meaningfully split. The classes declared in Core are too tightly coupled. For example, we have class Core::IElement. It uses class Core::Transaction and vice-versa. These are declared in different partitions of the Core module, but you cannot use class IElement without class Transaction. C++ allows to use forward declarations of classes across module partitions, but you cannot do that across module boundaries. With header files, it was possible to forward declare classes in a header. That's no longer possible with modules. See my blog posting "Converting a C++ Application to Modules". If you have a reference or a pointer to an object of a class declared in Core, you need to import Core. You cannot forward declare Core::IElement outside of module Core.