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_at_[hidden]rg>
Send Time:2022 May 25 (Wed.) 13:19
To:C++ EWG Reflector <ext_at_[hidden]>; WG21 Tooling Study Group SG15 <sg15_at_[hidden]>
Cc:Nicolai Josuttis <nico_at_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