stdlib_logger: structure of the different log messages?

[jvdp1]

With the PR #261, a hierarchy of levels for the different types of log messages was added in stdlib_logger led by @wclodius2 . Currently the user can only choose a level from which all messages with a level higher than the chosen level can be written. See these specs for more details on the different levels.

During the review of the #261, @ivan-pi proposed another possibility that would consider the different levels as switches.
Usig a binary representation of integers, levels would look like:

none_level = 0
text_error_level = shiftl(1,0) 
io_error_level = shiftl(1,1) ! or the error levels can have the same switch
error_level = shiftl(1,2)
warning_level = shiftl(1,3)
information_level = shiftl(1,4)
debug_level = shiftl(1,5)
all_level = text_error_level + io_error_level + error_level + warning_level + &
                 information_level + debug_level

This representation would allow the user to turn on selectively only certains combinations of log messages needed to be written to the output.

I often use stdlib_logger and I am happy with the current behaviour. However, I can see the advantages of such an approach.

What do you think?

[wclodius2]

I am also happy with the current behavior. I worry that allowing arbitrary combinations of levels would be hard to reason about, and hard to test (With six levels I believe there are 64 different combinations).

[milancurcic]

I think this approach could work well if we had levels in a flat, rather than hierarchical (i.e. info, warning, error). What are some examples of log levels that are not hierarchical (io could be one of them)?

I'm not a likely user of this potential feature and am happy with the current behavior.