How can I access implicit "implicit" i.e. def a[A :B] or def a[A <% B]?

Question

for example I need to access manifest in function def a[A:ClassManifest] to get erasure class. I can use Predef.implicitly function but in that case my code will be as long as if I use full form def a[A](implicit b:ClassManifest[A]). So is there are convenient generated names for those implicit arguments?

Answer 1

There are three predefined methods in Predef that will do it for Manifests, ClassManifests and OptManifests: manifest[T], classManifest[T] and optManifest[T], respectively. You can write your own such “implicit getters” for other type classes according to the same pattern. Here is for instance manifest[T]:

def manifest[T](implicit m: Manifest[T]) = m

So here's how you could write your own:

trait UsefulTypeclass[A] {
  def info = 42 // sample method
}

// the “implicit getter”
def usefulTypeclass[A](implicit tc: UsefulTypeclass[A]) = tc

// a method that uses the implicit getter
def foo[A: UsefulTypeclass] =
  usefulTypeclass[A].info