Better error handling

[suhr]

% tune scale 440 equal 31                                                                                                                                                                                                                      
thread 'main' panicked at 'Ratio must be finite and positive but was 0', /home/suhr/.cargo/registry/src/github.com-1ecc6299db9ec823/tune-0.10.0/src/ratio.rs:49:9
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

There's a handy crate for error handling: https://docs.rs/anyhow

[Woyten]

Hello @suhr! Thanks for your issue submission!

I am constantly working on improving the error handling concept. Unfortunately, I have no idea how to handle the error you reported as it is a numerical error which can occur at too many locations.

My strategy was to report all regular errors via Result and all numerical errors via .expect("..."). Do you have a good idea how numerical errors should be handled?

[Woyten]

I am closing this issue with the following outcome:

• Ratio operations no longer panic (to be released with tune-0.25.0). As a result, invalid float values (e.g. negative ones) are accepted by the API and can lead to non-finite (-inf, +inf, NaN) cents values. This is acceptable since all values passed to the API - including finite ones - need to be correct anyway.
• API code using expect in newer modules is expected to be rewritten without panics and with type-level numerical checks soon.
• Panics in executable code are okay.
• Code using unwrap is expected to never crash. If it does nonetheless, this is considered a bug.
• If a panic is observed in the API code, this is considered bug.