Traits and abstract methods override in Scala

scala, traits

Solution

You were very close. Add the abstract modifier to M.foo, and you have the 'Stackable Trait' pattern: http://www.artima.com/scalazine/articles/stackable_trait_pattern.html

trait Foo {
  def foo()
}

trait M extends Foo {
  abstract override def foo() {println("M"); super.foo()}
}

class FooImpl1 extends Foo {
  override def foo() {println("Impl")}
}

class FooImpl2 extends FooImpl1 with M

Problem

I have a base abstract class (trait). It has an abstract method `foo()`. It is extended and implemented by several derived classes. I want to create a trait that can be mixed into the derived classes so that it implements `foo()` and then calls the derived class's `foo()`. Something like: ``` trait Foo { def foo() } trait M extends Foo { override def foo() { println("M") super.foo() } } class FooImpl1 extends Foo { override def foo() { println("Impl") } } class FooImpl2 extends FooImpl1 with M ``` I tried self types and structural types, but I can't get it to work.

Original source