Generic的访问方法，用于扩展特征

Question

for getting a bit deeper into Scala I play around with a mysql wrapper. No production stuff, just experimenting.

I have a trait which specifies an abstract method:

trait EntityDefinition {
  def tableName: String
}

Then I have a parameterized class where I want to access tableName:

class FinagleRepository[T >: EntityDefinition] @Inject()(client: FinagleMysqlClient) {
  def create(entity: T): Future[Result] = {
    // Here it is impossible to call T.tableName
  }
}

Can anyone tell me what I am doing wrong?

Answer 1

You're currently defining EntityDefinition to be a lower bound for T , meaning T should be a supertype of EntityDefinition . What you actually want is for EntityDefinition to be a an upper bound for T , meaning T to be a subtype of EntityDefinition :

class FinagleRepository[T <: EntityDefinition]