Scala generics function call

Question

I have the following trait in scala:

trait BaseDao {

 type T <: BaseModel

 def saveModel(model: T)

}

I created a class which extends BaseDao:

 class Sample (dynamoDBMapper: DynamoDBMapper) extends BaseDao with LazyLogging {
 checkNotNull(dynamoDBMapper)

 protected def classType: Class[T] = implicitly[ClassTag[T]].runtimeClass.asInstanceOf[Class[T]]

 override def saveModel(model: T): Unit ={
   model.validate()

   dynamoDBMapper.save(model)
 }

Now, when I create the instance of above class and try to call save method:

    val testModel = new TestModel();
    testModel.setHashKey("a")
    testModel.setSortKey("b")
    testModel.setCreatedOn(new Date())
    testModel.setModifiedOn(new Date())

    sample.saveModel(testModel)

It gives the following error:

Type mismatch expected: Sample#T, actual: TestModel model class extends BaseModel class

I am new in scala and I am not able to figure out what is wrong here?

Markus Appel · Accepted Answer · 2019-01-23 15:03:16Z

1

You haven't defined type T in Sample.

Rewrite your Sample class to look somewhat like this:

class Sample (dynamoDBMapper: DynamoDBMapper) extends BaseDao with LazyLogging {

  checkNotNull(dynamoDBMapper)

  type T = TestModel

  override def saveModel(model: T): Unit ={
   model.validate()

   dynamoDBMapper.save(model)
  }
}

answered Jan 23, 2019 at 15:03

Markus Appel

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