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Implement initial version of C++20 module boost.type_index (#15)

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`#include <boost/type_index...` is now implicitly does `import boost.type_index` if the modules are supported 
All the library internals now have unconditional module level linkage.

Significant differences from https://anarthal.github.io/cppblog/modules3:
* `BOOST_TYPE_INDEX_USE_STD_MODULE` macro switch for `import std;` / `includes` while building module. This allows to use module in C++20 and even without usable  `std` module.
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Antony Polukhin
2025-05-12 17:35:17 +03:00
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parent 14ee2581bd
commit dc78cf1825
26 changed files with 469 additions and 43 deletions
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doc/type_index.qbk
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@ -1,6 +1,6 @@
[library Boost.TypeIndex
[quickbook 1.6]
[version 4.1]
[version 4.2]
[copyright 2012-2025 Antony Polukhin]
[category Language Features Emulation]
[license
@ -314,6 +314,40 @@ Sometimes there may be a need to create your own type info system. This may be u
[endsect]
[section C++20 module]
[caution C++20 module support is on early stage, targets, flags and behavior may change in the future]
If using modern CMake define CMake option `-DBOOST_USE_MODULES=1` to build a C++20 module and
make the `Boost::type_index` CMake target provide it. After that an explicit usage of C++20 module `boost.type_index` is allowed:
[import ../modules/usage_sample.cpp]
[type_index_module_example]
The `Boost::type_index` CMake target gives an ability to mix includes and imports of the library in different translation units. Moreover,
if `BOOST_USE_MODULES` macro is defined then all the `boost/type_index/...` includes implicilty do `import boost.type_index;` to give all the
benifits of modules without changing the existing code.
[note For better compile times make sure that `import std;` is available when building the `boost.type_index` module (in CMake logs there should be
a 'Using `import std;`' message). ]
If not using CMake, then the module could be build manually from the `modules/boost_type_index.cppm` file.
For manual module build the following commands can be used for clang compiler:
```
cd type_index/modules
clang++ -I ../include -std=c++20 --precompile -x c++-module boost_type_index.cppm
```
After that, the module could be used in the following way:
```
clang++ -std=c++20 -fmodule-file=boost_type_index.pcm boost_type_index.pcm usage_sample.cpp
```
[endsect]
[section Space and Performance]