Documentation for specializing type_conversion<> doesn't fully explain indicators about soci HOT 1 CLOSED

@creste sorry for delay, but haven't had time to compile a comprehensive answer to your question, a very interesting issue, by the way.

I have been trying to reach Maciej about original design background, if he replies it may clarify a lot.
Meanwhile, a brief answer to the three questions based on my own understanding. So, AFAIU:

1. Yes, I'd expect indicator must be set or we decide explicitly on some default value and related behaviour.
2. It is output variable.
3. I'd expect, in soci::use(myType, i_null) that the value is ignored and, presumably, SOCI assigns SQL NULL to corresponding placeholder in query. I understand that the indicator correspondence with semantic of SQL NULL, thus wherever user sets soci::i_null, s/he means SQL NULL.

But, all these needs to be verified, either by Maciej's response or by inspection of current implementation and corrections applied if needed, so the semantics and behaviours are intuitive and consistent. I think this is important topic, but I have to complete the SOCI 3.2.0 release first.

from soci.