Implicit in Scala

Implicit is another exciting and powerful feature introduced by Scala, and it can refer to two different things:

• A value that can be automatically passed
• Automatic conversion from one type to another
• They can be used for extending the capabilities of a class

Actual automatic conversion can be with implicit def, as seen in the following example (supposing you are using the Scala REPL):

scala> implicit def stringToInt(s: String) = s.toInt
stringToInt: (s: String)Int

Now, having the preceding code in my scope, it's possible for me to do something like this:

scala> def add(x:Int, y:Int) = x + y
add: (x: Int, y: Int)Int

scala> add(1, "2")
res5: Int = 3
scala>

Even if one of the parameters passed to add() is a String (and add() would require you to provide two integers), having the implicit conversion in scope allows the compiler to automatically convert from String to Int. Obviously enough, this feature could be quite dangerous, because it makes the code less readable...