Scala

# () => Int vs => Int

If you say f: () => Int, then you mean that "f takes no parameters and produces an Int".

If you say f: => Int, then you mean that "delay the execution of whatever statement produces 
an Int value until we use it in this code (and re-evaluate it each time)". 
Functionally, this ends up being basically the same as f: () => Int 
(and internally is converted into the same Function0 class), but it has a different usage, 
presumably to allow for a more compact form of closures (you always omit the => in the calling code).

http://stackoverflow.com/questions/3855595/what-is-the-scala-identifier-implicitly
Scala 2.8 allows a shorthand syntax for implicit parameters, called Context Bounds. Briefly, a method with a type parameter A that requires an implicit parameter of type M[A]:

def foo[A](implicit ma: M[A])
can be rewritten as:

def foo[A: M]

https://jaceklaskowski.gitbooks.io/mastering-apache-spark/content/spark-streaming-windowedoperators.html