hseeberger / slf4s

Scala 3 sugar for efficient logging

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slf4s is a library providing convenient and performant logging for Scala 3. It piggybacks on SLF4J and it automagically applies the check-enabled-idiom thanks to Scala 3 metaprogramming.

In a nutshell, you can invoke logging methods like info without checking whether the respective log level is enabled, because that exact check is handled for you by the compiler:

val expensive = "expensive"
val logger = Logger(getClass)
logger.info(s"I am an $expensive log message!") // unnecessary String interpolation?

The compiler will – more or less – create the following code for you:

if (logger.isInfoEnabled)
  logger.info(s"I am an $expensive log message!")

So if the respective log level is not enabled, the potentially expensive construction of the log message will not happen, even though you do not have to spend any efforts on that.

Further slf4s makes it easy to work with MDCs (a.k.a. context maps):

withMDC("key1" -> "value1", "key2" -> "value2") {
  logger.info("Some message")
  logger.info("Some other message")

The withMDC method takes one or more MDC entries (key-value-pairs) and a block of code. Within that block the key-value-pairs are put on the MDC and removed afterwards even in the case of an exception.

slf4s is inspired by:

Contribution policy

Contributions via GitHub pull requests are gladly accepted from their original author. Along with any pull requests, please state that the contribution is your original work and that you license the work to the project under the project's open source license. Whether or not you state this explicitly, by submitting any copyrighted material via pull request, email, or other means you agree to license the material under the project's open source license and warrant that you have the legal authority to do so.


This code is open source software licensed under the Apache-2.0 license.