Possibility to have a variable/expression as log level

[davidrohr]

I am trying to do something like:

LOG(foo == bar ? warning : error) << "this can be a warning or an error";

Is this possible with fairlogger (without an if/else and 2 LOG statements?
Or would it make sense to extend the API to support such a case?

[rbx]

Well, I came up with this:

#define FAIR_LOG_IF2(condition, severity1, severity2) \
    for (fair::Severity s = (condition ? fair::Severity::severity1 : fair::Severity::severity2), fairLOggerunLikelyvariable3 = fair::Severity::info; !fair::Logger::SuppressSeverity(s) && fairLOggerunLikelyvariable3 != fair::Severity::debug; fairLOggerunLikelyvariable3 = fair::Severity::debug) \
        for (bool fairLOggerunLikelyvariable = false; fair::Logger::Logging(s) && !fairLOggerunLikelyvariable; fairLOggerunLikelyvariable = true) \
            fair::Logger(s, MSG_ORIGIN)

int i = 1;
FAIR_LOG_IF2(i > 0, warning, error) << "asdf";
FAIR_LOG_IF2(i < 0, warning, error) << "asdf";

[WARN] asdf
[ERROR] asdf

This code becomes super unreadable, especially since s should be turned into something unique also. Perhaps there is a more readable way.

But what's the use case? Why not just if/else? It seems that a message would rarely be the same for both error and warning.
I would hate to make the macros even less readable for this.