On 2020-04-06 20:01, Richard Hodges via Boost wrote:

Dear all,

With the upcoming Boost 1.73 release imminent, I felt it was worthwhile pointing out that latest gcc has a problem with Asio if the `-fconcepts` command line flag is set.

There is an issue in the Boost.Asio repo here relating to the manifestation of the bug in MSVC:

https://github.com/boostorg/asio/issues/312

and an issue here in the Boost.Beast repo:

https://github.com/boostorg/beast/issues/1884

It seems that the file boost/asio/detail/config.hpp was written when concepts support was not widespread and still in the concepts.ts stage.

The syntax and capabilities of concepts were subtly changed during standardisation, with gcc and MSVC only supporting the C++20 dialect.

Thus, compiling an Asio-based program with concepts enabled in either of gcc or MSVC fails unconditionally.

I'm wondering if anyone has Chris' ear and might ask him to indulge us with a fix prior to the 1.73 release.

I fear that by the time Boost 1.73 is in mainstream use, C++20 will be upon us we'll see an increase in issues and a loss of reputation as a result.

I think, your best bet is to report the problem to the upstream ASIO project[1] and explicitly ask for a fix in Boost.ASIO ASAP. [1]: https://github.com/chriskohlhoff/asio/