Question: I am definitely more than thrilled with the Scala type inference engine, but in a real world environment:

1. How much of a performance draw back is it?
2. When is the type inferred, at compile time or runtime?

Answer: 
This is mentioned in this answer by Martin Odersky : [Why does IntelliJ IDEA compile Scala so slowly?](https://stackoverflow.com/questions/3606591/why-does-intellij-idea-compile-scala-so-slowly) "Type inference is costly, in particular if it involves implicit search."
The question is where the problem with compile times in Scala being longer than in Java come from. Hard for me to say as I'm no compiler construction expert. What I can say is that type inference is obviously not costly in Kotlin and also not in Groovy2.0. What slows down Scala must be something else such as search for implicits.