Functions / methods in Scala. How does this work?

Question

I am new to Scala and have a hard time understanding all the ways of declaring and using functions. Can someone please explain, step by step, what is going on here?

I am

Answer 1

There are many things that are going on here and this is a pretty complex example to understand scala. But i'll try.

The route's type is Route, which is a type alias defined as type Route = RequestContext ⇒ Future[RouteResult] where RequestContext ⇒ Future[RouteResult] is a function that consumes RequestContext and produces Future[RouteResult].

path is a method that creates a Directive[Unit]. There is an implicit conversion that converts Directive[Unit] into a function Route => Route (simplified). A function can be called by method apply or with compiler sugar as (???) or {???}.

get is a method that creates a Directive[Unit] too and similar approach applies to it.

complete is of type StandardRoute that extends Route.

Knowing all this, we could uglify your example that will be written as

path("hello").apply { ctx =>
    val inner: Route = { ctx =>
      ctx.complete("done")
    }
    get.apply(inner).apply(ctx)
}