Scala：两个隐式的ManManets

Question

Say I have this function in a class:

  def serializeObject[O<:MongoModel, F<:FunnelJob](mongoObject:O):F = {
    grater[F].asObject(mongoObject)
  }

I will not be able to compile this because I need a manifest for O and F. But I am unable to actually use to implicit manifest calls

  def serializeObject[O<:MongoModel, F<:FunnelJob](mongoObject:O)(implicit mf:Manifest[O], implicit m:Manifest[F]):F = {
    grater[F].asObject(mongoObject)
  }

is invalid, for example. How can I have two generics with two manifests?

Answer 1

You only need one implicit keyword, it applies to the entire parameter list in this context:

def serializeObject[O<:MongoModel, F<:FunnelJob](mongoObject:O)(implicit mf:Manifest[O], m:Manifest[F]):F

Side notes:

1. you probably don't need Manifest[O] ;

2. when calling, you'll need to provide the type parameters explicitly or have a clear expected type, otherwise F will be inferred to Nothing ;

3. Manifest s are semi-deprecated and should be replaced by ClassTag or TypeTag in most cases. See http://docs.scala-lang.org/overviews/reflection/typetags-manifests.html .