Logger eagerly evaluates the message before checking the log level

[kamilkloch]

With log level set to INFO, the following snippet

logger.debug({ println("this should not be printed"); ""})

prints

this should not be printed

This is arguably an undesired behavior. Compare with https://github.com/lightbend-labs/scala-logging, where you can call log methods, without checking whether the respective log level is enabled.

[wsargent]

The first argument is an argument template, which takes a static string -- if you want to render an argument as the only thing in the template, you would typically do it using logger.debug("{}", Arguments("foo")).

You can use lazy blocks for preference:

logger.debug { debug =>
  val debugInfo = ...
  debug(st"I am a debugging statement with lots of extra $debugInfo")
}