CODEWITHSUNDEEP
scalapattern-matchingtraits
michaelmotorcycle
michaelmotorcycle

Reputation: 19

Scala: How do I check that a dynamically loaded class implements a trait?

I am trying to build a Scala application in which the user can load in classes that implement an interface defined by a trait, which the application will then use.

For example, my Operator trait

trait Operator {
    def operate(a: Int, b: Int): Int
}

is implemented by a user-defined class to be loaded in at run time, Add.

class Add {
  def operate(a: Int, b: Int): Int = a + b
}

How can the application check that this Add class implements the Operator trait it knows about? I would like to be able to call operate on an instance of the loaded class.

I have tried simple pattern matching like this

case op: Class[Operator] => op.newInstance()

but this appears to check implementation based on trait name rather than member signatures.

Upvotes: 0

Views: 557

Answers (1)

sarveshseri
sarveshseri

Reputation: 13985

First of all, lets clear the terminology, your class Add simply does not implement the Operator trait which you defined. You should not and can not use clearly defined terms to mean something different compared to their actual meaning.

Now, what you are looking for are structural types and not traits.

Lets define a strucural type with name IsOperator,

type IsOperator = {
  def operate(a: Int, b: Int): Int
}

And lets define something logic which uses this,

def perform(a: Int, b: Int, o: IsOperator): Int = o.operate(a, b)

Now, any object or instance of any class which confirms to the structural type IsOperate (has a method named operate with type (Int, Int) => Int) can be used with perform.

object Add {
  def operate(a: Int, b: Int): Int = a + b
}

val sum = perform(1, 2, Add)
// sum: Int = 3

Upvotes: 3

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