we already have generic operator<< based formatter for sequence-alike
ranges defined in `utils/to_string.hh`, but as a part of efforts to
address #13245, we will eventually drop the formatter.
to prepare for this change, we should create/find the alternatives
where the operator<< for printing the ranges is still used.
Boost::program_options is one of them. it prints the options' default
values using operator<< in its error message or usage. so in order
to keep it working, we define operator<< for `vector<sstring>` here.
if there are more types are required, we will need the generalize
this formatter. if there are more needs from different compiling
units, we might need to extract this helper into, for instance,
`utils/to_string.hh`. but we should do this after removing it.
Refs #13245
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
Closesscylladb/scylladb#17413
4ee2aee279