CODEWITHSUNDEEP
scalagenericsoperators
marius
marius

Reputation: 1613

Generic Operator in Scala

Is it possible to define generic operators in Scala?

Scala lets me map arbitrary operators on functions, which is incredibly useful. It seems restrictive however, in a case where I might want the operators to change given the state of the application.

To give an example: I have a table with users and a table with their respective relationships. Each relationship has a type, such as: "friends-with", "works-with", etc. Based on my domain model, I would like the DSL to allow for: is(john friends-with mary). In this case, both john and mary would be of Object User, which would have a generic operator def <relationship> (a:User): Boolean = {...}.

What I wanted to achieve was exactly what Dynamic would allow me to do (see answer). The description fits perfectly:

A marker trait that enables dynamic invocations. Instances x of this trait allow calls x.meth(args) for arbitrary method names meth and argument lists args. If a call is not natively supported by x, it is rewritten to x.applyDynamic("meth", args).

More information here: http://www.scala-lang.org/api/current/scala/Dynamic.html

Upvotes: 0

Views: 421

Answers (1)

Daniel C. Sobral
Daniel C. Sobral

Reputation: 297265

Look at trait Dynamic, which will be available on Scala 2.10 (it's experimental on Scala 2.9).

For example:

scala> :paste
// Entering paste mode (ctrl-D to finish)

case class User(name: String) extends Dynamic {
  def applyDynamic(relationship: String)(to: User) =
    Relation(relationship, this, to)
}
case class Relation(kind: String, from: User, to: User)

// Exiting paste mode, now interpreting.

defined class User
defined class Relation

scala> User("john") friendsWith User("mary")
res0: Relation = Relation(friendsWith,User(john),User(mary))

Upvotes: 4

Related Questions