Before I spend too long tracking this down (I'm only seeing it in an
Appveyor Windows build, since I do most of my work on Linux), I wanted
to see if anyone else has experienced this issue. I'm trying to use
boost::program_options to parse a command line arg and store it into a
boost::optional, however I get a surprising compilation error[1].
This appears to have been introduced sometime between Boost 1.60 and
1.62 (Appveyor doesn't have Boost 1.61). I see that there were some
significant changes to boost::optional between those revisions, so maybe
that's the cause? The following test case *might* reproduce the issue,
but sadly, rextester only has Boost 1.60, so it works there[2]. If it
fails for someone with Boost 1.62+, then great! (Well, not "great", but
you know what I mean.)
Interestingly, it's not until Boost 1.65[3] that boost::program_options
claims to support storing values into boost::optional; it's worked for
me since long before that, possibly because I `#include