CODEWITHSUNDEEP
scalaplayframework-2.0
Mik378
Mik378

Reputation: 22171

useless implicit keyword assigned to method ? / Play framework 2

As the official documentation of Play framework recommends, we can use an implicit request in order to improve access to some objects associated to the request.

Sample:

def index = Action { implicit request =>
  session.get("connected").map { user =>
    Ok("Hello " + user)
  }.getOrElse {
    Unauthorized("Oops, you are not connected")
  }
}

This is due to the addition of the following implicit method belonged to the Controller trait:

/**
   * Retrieves the session implicitly from the request.
   *
   * For example:
   * {{{
   * def index(name:String) = Action { implicit request =>
   *   val username = session("username")
   *   Ok("Hello " + username)
   * }
   * }}}
   */
  implicit def session(implicit request: RequestHeader) = request.session

Question: Why does this method is declared itself as implicit? Isn't it enough to only declare request parameter as implicit?

I expected to see that instead:

def session(implicit request: RequestHeader) = request.session

Upvotes: 0

Views: 329

Answers (1)

Régis Jean-Gilles
Régis Jean-Gilles

Reputation: 32719

The first implicit keyword is indeed not necessary at all to allow your sample to compile. So either it is an error in Play!, or the additional implicit keyword was intended to play another role.

In particular with this additional implicit keyword, you can call a method that expects an implicit value of type Session even if you only have an implicit value of type RequestHeader in scope (session also defines an implicit value of type RequestHeader , provided that you have an implicit value of type RequestHeader in scope).

Upvotes: 1

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