Some function arguments can be declared implicit.

Then, at compile-time, the only value matching the type of that argument is used. If there is no matching argument or there is more than one, then a compile-time error results.

Implicits appear like a potential problem at superficial glance, since what about side-effects?

But actually, we can encode an extremely powerful concept called type-classes^[15] with implicit arguments.

We can also do what the dynamic typing guys are doing, but with the advantage of safety^[16]

scala> implicit def i(s: String) = new { def parseInt = Integer.parseInt(s) }
i: (String)java.lang.Object{def parseInt: Int}

scala> val v = "456".parseInt
v: Int = 456