Trait Fields in Scala
I mentioned in an earlier post that methods declared, but not defined, are implicitly defined as abstract:
trait Foo {
def bar(x: String) // abstract definition
def baz(y: String) {} // concrete definition
}
The same goes with fields:
trait Foo {
val bar:Int // abstract field
val baz = 10 // concrete field
}
When a class inherits from a trait, these fields are placed into the subclass - not inherited. Note that the JVM itself only allows for one superclass, so traits can’t be inherited in the same way - hence this distinction.
It’s also worth noting that, when you are dealing with traits which contain abstract fields, you must override the field in the class itself - just like you must with methods. Some syntactic sugar includes that you do not need to add an override modifier in your class in order to initiate abstract fields.