CODEWITHSUNDEEP
scalatypesstructural-typing
bigwheels16
bigwheels16

Reputation: 892

accept multiple types for a parameter in scala

I have two objects, ObjectA and ObjectB, both with a method update(). I want to write a function that accepts either ObjectA or ObjectB (but no other types). Conceptually, this is what I am trying to do:

def doSomething[T <: ObjectA | T <: ObjectB](obj: T) = {
    obj.update
}

I realize there are other ways to solve this problem (eg, structural typing of the update() method, common base class, etc) but my question is it is possible to do it this way in Scala and if so what is the syntax? And what is this called?

Upvotes: 20

Views: 15811

Answers (2)

Guru Vishnu Vardhan Reddy
Guru Vishnu Vardhan Reddy

Reputation: 349

As mentioned in accepted answer, Either is perfectly suitable for your problem

Here's a solution when field members are not the same

def doSomething(obj: Either[ClassA, ClassB]): String = {
  obj match {
    case Left(objA) => objA.field1
    case Right(objB) => objB.field2
  }
}

doSomething(Left(new ClassA(field1="something")))

doSomething(Right(new ClassB(field2="somethingelse")))

Here's a solution when we have to accept multiple Types

def doSomething[T](obj: T): String = {
  obj match {
    case objA: ClassA => objA.field1
    case objB: ClassB => objB.field2
    case objC: ClassC => objC.field3
  }
}

doSomething(new ClassA(field1="something"))

doSomething(new ClassB(field2="somethingelse"))

doSomething(new ClassC(field3="another"))

Upvotes: 2

blouerat
blouerat

Reputation: 692

In Scala, there is the type Either to make a disjoint union. Basically, you will do something like:

def doSomething(obj: Either[ObjectA, ObjectB]) {
  obj.fold(fa, fb)
}

Checkout http://www.scala-lang.org/api/current/scala/Either.html

Upvotes: 21

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