Module rs::logging

Logging library.

This is probably the only part of squeekboard that should be doing any direct printing.

There are several approaches to logging, in the order of increasing flexibility and/or purity:

1. println! directly

It can’t be easily replaced by a different solution

2. simple log! macro

Replacing the destination at runtime other than globally would be awkward, so no easy way to suppress errors for things that don’t matter, but formatting is still easy.

3. logging to a mutable destination type

Can be easily replaced, but logging Result types, which should be done by calling a method on the result, can’t be formatted directly. Cannot be parallelized.

4. logging to an immutable destination type

Same as above, except it can be parallelized. Logs being outputs, they get returned instead of being misleadingly passed back through arguments. It seems more difficult to pass the logger around, but this may be a solved problem from the area of functional programming.

This library generally aims at the approach in 3.

Macros

• log_print 🔒
  Sugar for approach 2

Structs

• Print
  Prints info to stdout, everything else to stderr
• ProblemPanic
  Warning handler that will panic at any warning, error, surprise, bug, or panic. Don’t use except in tests

Enums

• Level
  Levels are not in order.
• Problem
  Only levels which indicate problems To use with Result::Err handlers, which are needed only when something went off the optimal path. A separate type ensures that Err can’t end up misclassified as a benign event like Info.

Traits

• Handler
  A mutable handler for text warnings. Approach 3.
• Warn
  Sugar for logging errors in results.

Functions

• print
  Approach 2