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.
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
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super.foo()do when foo is unimplemented in the super class?