Annotations

Provides the annotations of type A of the fields or constructors of case class-like or sum type T.

If type T is case class-like, this type class inspects its fields and provides their annotations of type A. If type T is a sum type, its constructor types are looked for annotations.

Type Out is an HList having the same number of elements as T (number of fields of T if T is case class-like, or number of constructors of T if it is a sum type). It is made of None.type (no annotation on corresponding field or constructor) and Some[A] (corresponding field or constructor is annotated).

Method apply provides an HList of type Out made of None (corresponding field or constructor not annotated) or Some(annotation) (corresponding field or constructor has annotation annotation).

Note that annotation types must be case class-like for this type class to take them into account.

Example:

case class First(s: String)

case class CC(i: Int, @First("a") s: String)

sealed trait Base
@First("b") case class BaseI(i: Int) extends Base
case class BaseS(s: String) extends Base


val ccFirsts = Annotations[First, CC]
val baseFirsts = Annotations[First, Base]

// ccFirsts.Out is  None.type :: Some[First] :: HNil
// ccFirsts.apply() is
//   None :: Some(First("a")) :: HNil

// baseFirsts.Out is  Some[First] :: None.type :: HNil
// baseFirsts.apply() is
//   Some(First("b")) :: None :: HNil