Removal of deprecated things

[Nerixyz]

Boost 1.87.0 (specifically ASIO 1.33¹) breaks https://github.com/zaphoyd/websocketpp by removing io_service and more (yes, I know about Boost.Beast).

It would be great if deprecated things were annotated with [[deprecated]] so one can get compiler warnings before the things are removed. If this gets too noisy, users could define BOOST_ASIO_NO_DEPRECATION_WARNINGS² or something similar. Explicitly opting out is much better than requiring opt-in. I'm okay with removing stuff in minor releases³, but it's important to actively notify users about it - expecting users to use BOOST_ASIO_NO_DEPRECATED or to actively check the documentation for all their used functions is not enough in my opinion, we have [[deprecated]] for a reason.

Footnotes

1. This release is not available in this repository, only in the Boost one. ↩

2. Or even better: BOOST_ASIO_NO_DEPRECATION_WARNINGS_SINCE(1, 33) to disable deprecations introduced after 1.33. ↩

3. Ideally, the project would use semantic versioning, but I understand that this isn't possible. ↩

[klemens-morgenstern]

Deprecated isn't C++11 though.

[Nerixyz]

Deprecated isn't C++11 though.

There isn't a dedicated feature-test macro for this, but testing for __cplusplus should be enough:

#if __cplusplus >= 201402L // C++ 14
  #define ASIO_DEPRECATED [[deprecated]]
  #define ASIO_DEPRECATED_X(msg) [[deprecated(msg)]]
#else
  #define ASIO_DEPRECATED
  #define ASIO_DEPRECATED_X(msg)
#endif

tbf, allowing newer deprecations ("disable deprecations after 1.xx") is a bit harder, because the macros would need to be "unrolled" i.e. there would need to be a macro for each version (e.g. ASIO_DEPRECATED_1_33).