which version of bitcoin core is suitable for debugging ?

[maplelake]

I download the latest bitcoin core 0.19 to build, debug. But I found it is easy to lost in the "forest of code path".No wonder that the code base grows 10+years. A lot of feature,bug fix in it.

any suggestion ? which version is good playground ?

ps: In last some years I've read several books like "master bitcoin". "master bitcoin2". some online bitcoin video course. go through knowledge base "bitcoin.org"/bitcoin wiki. read tech-blog from time to time. But i feel that i still in puzzle for many things. I mean, known is known, unknown is unknown. Even you know sth in post, but you still do not understand it.
until some months ago, I start to playground on code by debugging. I find I make a progress.
I think now debugging is alternative to move forwards.
 
you know sth, you learn sth. you understand sth. Then you could think in "sth". until now you might create sth.
that is my thinking.
comments is welcome. 

[achow101]

What, exactly, are you trying to do or learn?

Old code is probably not easier to learn. It's often more complicated or does not separate things that should conceptually be separate. While the current codebase is fairly complex and tracing functions requires jumping around a lot, it should still make more sense than old code where everything was in one place and all mixed together.