Alternatively, things like this is why it is great when everyone works together to improve one lib rather instead of forming their efforts on two essentially-identical ones. You act like libc++ is somehow simply better and probably doesn't have bugs :/. I have been doing C++ work now for over two decades and let me set that record straight in your head: incredibly basic stuff has been pretty extremely broken in libc++. One horror story that wasted way way too much of my life is that the copy that Mac OS X 10.7 seriously shipped with a build of libc++ where std::streambuf failed to check EOF conditions correctly. Despite most of my projects being compiled simultaneously by numerous versions of both gcc and clang (to target various weird configurations), I seriously don't remember the last time I ran into a bug in gcc and libstdc++... it was pre-2006 for sure... but I continue to run into annoying issues with clang and libc++. The correct way to read "modern" when applied to "codebase" is "untested". And hell: while I am totally willing to believe there is a bug here, this post doesn't have a fix and doesn't even seem to have led to a bug report. This is like saying "I compiled my code using -O0 and it started working, so clearly this is a bug in the optimizer", which we should all know is a dubious statement at best.

Alternatively, having a choice of more than one thing tends to cause competition to kick in, which often results in better quality than a single solution that everyone pretty much has to use.