Scala Generics : Cannot write an instance of T to HTTP response. Try to define a Writeable[T] -

following code when written using generic give compilation error.

without generic

def getdata(id: string) = action.async {      val items = getitems(id)      sendresult(items)   }    private def sendresult(result: future[any]) = {       result.map {       items => {         try {           val itemstr = items.asinstanceof[string]           ok(itemstr)         } catch {           case t: classcastexception => internalservererror(s"casting exception while processing output $t")         }       }     }.recover {       case t:timeoutexception => internalservererror("api timed out")       case t: throwable => internalservererror(s"exception in api $t")     }   } 

with generic

  def getdata(id: string) = action.async {      val items = getitems(id)      sendresult[string](items)   }    private def sendresult[t](result: future[any]) = {       result.map {       items => {         try {           val itemstr = items.asinstanceof[t]           ok(itemstr)         } catch {           case t: classcastexception => internalservererror(s"casting exception while processing output $t")         }       }     }.recover {       case t:timeoutexception => internalservererror("api timed out")       case t: throwable => internalservererror(s"exception in api $t")     }   } 

the code part of play app's contorller method. first 1 works fine. second 1 gives following compilation error

cannot write instance of t http response. try define writeable[t] [error] ok(itemstr) [error]

using any generic function doesn't make sense.

private def sendresult[t](result: future[any]) // should better private def sendresult[t](result: future[t]) // ... remove unsafe cast 

then t needs provided instance of writeable, can written array[byte] on network.

// either ... private def sendresult[t: writeable](result: future[t]) // ... or ... private def sendresult[t](result: future[t])(implicit w: writeable[t])