Let's dive more into object oriented programming ideas but with a dash of functional programming.
The idea today is to go a bit further withtraitand be able to describe behaviors ofhigher kinds. It is just a fancy terms to describe type that accept type as parameter, such asList[A], theAbeing the type accepted as parameter.
To create a generic trait that “target” type that take type(s) as parameter, the syntax is:
trait MyTrait[F[_]]
TheF[_]means that we are expecting a typeFthat take one type parameter as argument, the_.
Note that it is possible to target a type that takes two types as input with the following syntax:F[_, _]. You can imagine that it is possible to target type with more than two following the same logic.
When you use a parameterized type you do something likeList[Int]so if you want to use the type itself you simply has to doTrait[List], not need to add anything after theList.
You also noticed that you can create your own type and it will behave the same way. Look atCounterTin our example. It takes one type as parameter so it can be used with ourtrait.