Q1: Why is this still fenced off in the 'experimental' namespace? My understanding is that this facility officially merged into the mainstream with C++17.
Q2: The file '/Library/Developer/CommandLineTools/usr/include/c++/v1/experimental/memory_resource' mentions 'monotonic_buffer_resource' in the synopsis, but does not appear to implement it. Does a more recent recent version of the Xcode command line tools provide it?