Implicit injection

We already saw implicits at a few places in this book. We used them in the type class design pattern, the pimp my library design pattern, and we also mentioned that they can be used for dependency injection. Implicits are also used for conversions from one type to another silently.

They are nothing more than some objects, values, or methods that the compiler knows about and injects for us into methods or places that need them. What we need to make sure is to make these implicits available to the scope of the methods that would use them.

Implicit conversions

We have already mentioned that implicits can be used for silent conversions. Sometimes it might be useful to be able to assign a Double to an Int and not get an error. Other times we might want to wrap an object of one type into another and take advantage of the methods the new one provides.

package object implicits {

  implicit def doubleToInt(a: Double): Int = Math.round(a).toInt
}

In the preceding code listing, we have...