example: register the shared classes in both modules, as Windows requires

[jll63]

(Written by Claude Code, on behalf of @jll63.)

The implicit_linking example aborts on Windows, and always has:

unknown class struct Wolf

extensions.cpp — the DLL — registers Animal, Herbivore, Cow,
Carnivore and Wolf. main.cpp creates a Wolf with new and dispatches on
it. Windows keeps one type_info object per module, so the program's Wolf and
the library's Wolf are two different type ids, and only the library's was ever
registered. ELF and Mach-O merge the two, which is why it passes everywhere
else.

This is the case cpp:use_classes[] already documents:

If a class is identified by different type ids in different translation units,
it must be registered in as many translation units as necessary … The only
such case known to the author is when using Windows DLLs.

The example was the one place that did not follow its own rule. The program now
registers the library's classes as well — redundant and harmless on ELF, and
what makes the example work on Windows. shared_libraries.adoc says why, next
to the example, since the extra line would otherwise look like an oversight.

Not a regression

Measured with MSVC v18 BuildTools, Ninja, Release, against three trees:

tree	result
7eb56f5 — "support DSO/DLL on all platforms (#75)", the commit that added the example	fails
develop	fails
this branch	passes

There is no good commit to bisect to; it has never worked on Windows.

Why CI never caught it

The doc examples are built only when this project is configured as the root
with BOOST_OPENMETHOD_BUILD_TESTS=ON, which no CI job does: the Boost.CI jobs
build the library inside the super-project, where that option defaults to OFF,
and b2's test/Jamfile globs test_*.cpp and compile_fail_*.cpp only. So
boost_openmethod-static runs in a local root CMake build and nowhere else, on
any platform.

Worth considering separately — not in this PR — whether one CI job should
configure the project as root with examples on, or this class of breakage stays
invisible.

Tests

186/186 under gcc 13.3 Release with warnings as errors; the affected test
verified directly under MSVC as above. The existing
test/implicit_shared_libraries tests are unaffected — they already register
their classes in both modules, which is why they pass on Windows today.

🤖 Generated with Claude Code

https://claude.ai/code/session_01RQG6CbE4o2agseE7bDVzHS

[cppalliance-bot]

An automated preview of the documentation is available at https://114.openmethod.prtest3.cppalliance.org/libs/openmethod/doc/html/index.html

If more commits are pushed to the pull request, the docs will rebuild at the same URL.

2026-09-16 00:57:04 UTC

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.25%. Comparing base (d44aa59) to head (f4fc118).
⚠️ Report is 4 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #114      +/-   ##
===========================================
- Coverage    93.51%   93.25%   -0.26%     
===========================================
  Files           22       22              
  Lines         1695     1706      +11     
  Branches       504      509       +5     
===========================================
+ Hits          1585     1591       +6     
- Misses          66       71       +5     
  Partials        44       44              

see 1 file with indirect coverage changes

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