Why can't a class extend traits with method of the same signature?

overriding, scala, traits

Solution

This works for me in 2.8 and 2.11, and would allow you to be non-intrusive in traits `A` or `B`:

trait A { def hi = println("A") }
trait B { def hi = println("B") }

class C extends A with B {
  override def hi = super[B].hi
  def howdy = super[A].hi // if you still want A#hi available
}

object App extends Application {
  (new C).hi // prints "B"
}

Problem

Why do I get the error below? How to workaround it? I assumed that since A and B compile to (interface,class) pairs, it's a matter of choosing the right static method call to implement when compiling C. I would expect the priority to be according to order. ``` scala> trait A { def hi = println("A") } defined trait A scala> trait B { def hi = println("B") } defined trait B scala> class C extends B with A <console>:6: error: error overriding method hi in trait B of type => Unit; method hi in trait A of type => Unit needs `override' modifier class C extends B with A scala> trait A { override def hi = println("A") } <console>:4: error: method hi overrides nothing trait A {override def hi = println("A")} ``` Note that in Ruby this works well: ``` >> module B; def hi; puts 'B'; end; end => nil >> module A; def hi; puts 'A'; end; end => nil >> class C; include A; include B; end => C >> c = C.new => #<C:0xb7c51068> >> c.hi B => nil ```

Original source