| Issue |
138906
|
| Summary |
[C++20] [Modules] [std module] Implicitly import std if standard library header is included
|
| Labels |
new issue
|
| Assignees |
|
| Reporter |
apolukhin
|
What do you think about the following idea: add a preprocessor macro that replaces content of the header with `import std;` if the macro is defined by user.
For example libcxx/include/vector can be changed in the following way:
```
#ifndef _LIBCPP_VECTOR
#define _LIBCPP_VECTOR
#if defined(LIBCPP_IMPLICIT_MODULES_USE)
import std;
# include <version>
#else
... // all the remaining code from <vector>
#endif // LIBCPP_IMPLICIT_MODULES_USE
#endif // _LIBCPP_VECTOR
```
Motivation:
1. Implicit `import std;` in standard library header would improve compile times if module std is available.
2. Migration from includes to `import std;` for big projects is not trivial. The above approach eases that migration
3. It's a possible alternative solution to https://github.com/llvm/llvm-project/issues/80663
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