scala - useless implicit keyword assigned to method ? / Play framework 2 -

as official documentation of play framework recommends, can use implicit request in order improve access objects associated request.

sample:

def index = action { implicit request =>   session.get("connected").map { user =>     ok("hello " + user)   }.getorelse {     unauthorized("oops, not connected")   } } 

this due addition of following implicit method belonged controller trait:

/**    * retrieves session implicitly request.    *    * 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 method declared implicit? isn't enough declare request parameter implicit?

i expected see instead:

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

the first implicit keyword indeed not necessary @ allow sample compile. either error in play!, or additional implicit keyword intended play role.

in particular additional implicit keyword, can call method expects implicit value of type session if have implicit value of type requestheader in scope (session defines implicit value of type requestheader , provided have implicit value of type requestheader in scope).