Hi Nicolai,

   I think the header unit might be wanted. It allows us to import headers just like modules:

```

import <iostream>

```

   If we want named modules, we could use the following tricks:

```

module;

#include "headers"

export module named_module;

export the things we want to export;

```

   In this form, we need to write additional code but we avoid double-written.

Thanks,

Chuanqi

------------------------------------------------------------------

From:Nicolai Josuttis via Ext <ext@lists.isocpp.org>

Send Time:2022 May 25 (Wed.) 13:19

To:C++ EWG Reflector <ext@lists.isocpp.org>; WG21 Tooling Study Group SG15 <sg15@lists.isocpp.org>

Cc:Nicolai Josuttis <nico@josuttis.de>

Subject:[isocpp-ext] How to provide functionality as both header file and module?

I need your help.

One of my customers wants to start using modules.
So far, they use traditional header files, which should now step-by-step become modules.

However, their code is not necessarily only used within projects that use a build system.
It is a little piece of functionality useful in all kinds of programs (a key attribute of header files today).

Initially, I told the customer that AFAIK modules can be used everywhere.
But I learned that Microsoft decided to require using a build system when using modules.
And I learned here that this is intentional and OK.

Telling that my customer, they raise a very obvious question:

 How can they provide code that can be used in both software that uses a build systems and software that doesn't?

They want to avoid double-written code or scripts to transform code form one format to another (header files to module or vice versa)

And they really do not want to deliver/provide two different files of C++ code for the same functionality.

Which results in the following question:

 What is the best approach / trick / hack to provide single-source code that can be used as both header file and module?

Or should customers in situations like this not replace header files by something that supports modules at all?

-- 
--- 
Nicolai M. Josuttis
www.josuttis.de
+49 (0)531 / 129 88 86
+49 (0)700 / JOSUTTIS

Books:
 C++: http://cppstd20.com, http://cppstd17.com, http://cppmove.com,
      http://cppstdlib.com, http://tmplbook.com