https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99058
--- Comment #3 from Brad Spencer <bspencer at blackberry dot com> --- (In reply to Jonathan Wakely from comment #1) > C++17 support isn't stable until GCC 9 so there is no guarantee of > compatibility between 7 and 8 or 8 and 9. That applies to the entire library > (and language features) not just std::optional. Ok. What's the right way for me to learn what version of GCC has stable support for a C++ version? For example, where would I look to know that C++17 support isn't stable until GCC 9? I can't seem to find that information on the status page, but maybe I am looking in the wrong place. (In reply to Jonathan Wakely from comment #2) > (In reply to Brad Spencer from comment #0) > > Perhaps I was misusing this table, but I interpreted "supported since 7.1" > > to mean that if I compile against 7.1 headers, my code will remain ABI > > compatible against future versions of the library _and_ other code compiled > > against future versions of the headers. > > Absolutely not. Sorry. I was imprecise in my wording. I am not looking for or expecting any guarantees. I am under the (possibly mistaken) impression that the libstdc++ ABI (in a given configuration) has been stable for a very long time, and that generally integrators (such as Debian or Ubuntu, for example) provide versions of libstdc++ that are ABI-compatible with code compiled against previous versions. As per https://gcc.gnu.org/onlinedocs/libstdc++/manual/abi.html this is reflected in the long-standing .so major version of 6. I know there are many caveats here, especially around the early introduction of pre-standardized features, etc. Is it correct to think that the _intention_ is that it is possible to configure the library to remain ABI compatible into the future until a conscious decision is made to introduce an ABI break? Or, if I ever run code compiled with GCC N against the library from GCC N+1, am I always at risk, with not even best efforts to lean on? I'm not asking you to do more. I just want to get a good understanding of the circumstances of ABI stability.
