libpqxx 8.0.0 release candidate 3

[jtv]

Here's another release candidate for libpqxx 8.0. With your feedback, contributions, and sometimes in-depth research, we have a lot of further improvements compared to the previous release candidate!

One big change is that you can now convert directly between simple one-dimensional SQL arrays and C++ containers such as std::vector<int> or std::list<std::string> etc. You can stream these values,read them from a pqxx::result using a field's as<...>() member function, and pass them as parameters.

(The conversion to string was already there but it wasn't working because of a small omission.)

Other important changes:

• You can now use std::string_view in more places that previously required pqxx::zview.
• There's an examples/ directory with working, compiling example code.
• We no longer support the JOHAB encoding. It's a deprecated encoding, and it doesn't look like the backend support was ever complete. Also... which variant of JOHAB? There's several.
• In general, the text handling got smaller, simpler, and more efficient.
• Compiler errors should be slightly clearer when you're writing your own string conversions and struggling to meet the API.
• Several pqxx::result member functions now take pqxx::sl (i.e. std::source_location) rather than pqxx::conversion_context.
• MSVC 2022 didn't actually support multi-dimensional operator[] in C++23 mode. The build now detects that problem.

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This discussion was created from the release libpqxx 8.0.0 release candidate 3.