How do I leveraging SLF4J varargs logging in Play2.1 framework? - scala

Question

SLF4J's varargs on the logging calls are quite useful in my Java work
Logger log = LoggerFactory.getLogger( getClass() );
log.debug( "Hello, {}. The current time is {}", "robert", new Date() );
Attempting to do this simple example in Play 2.1 Framework/Scala and I run into the compiler rejecting me.
import play.api._
import play.api.mvc._
import org.slf4j.LoggerFactory
object Application extends Controller {
val log: org.slf4j.Logger = LoggerFactory.getLogger(getClass())
def hb = Action {
val message = makeMessage()
// COMPILER HATES THIS: ambiguous reference compiler error here
log.info("Hello {}. The current time is {}", "robert", new java.util.Date() )
Ok(message)
}
def makeMessage(): String = { return "stuff" }
}
[dm2-server] $ compile
[info] Compiling 2 Scala sources to /Users/bobk/work/dm2-server/target/scala-2.10/classes...
[error] /Users/bobk/work/dm2-server/app/controllers/Application.scala:16: ambiguous reference to overloaded definition,
[error] both method info in trait Logger of type (x$1: String, x$2: <repeated...>[Object])Unit
[error] and method info in trait Logger of type (x$1: String, x$2: Any, x$3: Any)Unit
[error] match argument types (String,String,java.util.Date)
[error] log.info("Hello {}. The current time is {}", "robert", new java.util.Date() )
[error] ^
[error] one error found
[error] (compile:compile) Compilation failed
[error] Total time: 1 s, completed Jun 6, 2013 10:54:41 AM
What is that error and how do I overcome it to call through to the SLF4J API? If I can't do that, how can I use the Play 2.1 Logging Framework to get varargs on my logging calls? Something is not right in Scala-land.

Answer 1

What version of SLF4J are you using? If you can go back to 1.6.6 or later, you can avoid this issue in ambiguity. Those two signatures unfortunately look the exact same to scala and the compiler can't seem to differentiate which one you mean. The common suggestion is to roll back to a version of SLF4J (if even possible for you) where this overloaded method ambiguity will not exist. More info can be found at the links below:
https://groups.google.com/forum/?fromgroups#!topic/scala-language/ms4IVIu-xGw
https://github.com/typesafehub/scalalogging/issues/16

Answer 2

The "quick fix" for this is as follows:
Just force the last argument to be type Any and that resolves the compiler's issue(s) (and makes for slightly less code...)
logger.debug("hello {} / {} ", "Hello", "World":Any)
Or in your case:
log.info("Hello {}. The current time is {}", "robert", new java.util.Date():Any)