Does turbodbc still need boost as a dependency?

[bgemmill]

The C++ standard library has been absorbing concepts from boost, and it looks like it may be close to providing everything turbodbc needs, depending on which standard turbodbc wants to target.

From here, it looks like the required boost libraries are variant, optional, datetime, and locale.

C++17 has variant, optional, C++11 has chrono and C++20's chrono has a standardized date, and it looks like boost::locale may have been removed already.

Depending on the date formatting required, it may be too soon to consider requiring the standard library from 20, but this seemed interesting to bring up.

[alippai]

Does this look good? #466