In languages like C/C++/Objective-C it's common to use preprocessor macros to define logging mechanisms that are not even compiled for released binaries, thus causing no performance hit. Something along the lines of:
#ifdef DEBUG
printf("some event we want to log\n");
#endif
Now, I know there's no preprocessor in Scala. So my question is: what is the best way to implement a mechanism to log program activity for debug purposes, while impacting performance the least when it's turned off?