Scala：如何使子类可以访问受保护的方法（在其他实例上）？

Question

I'm trying to do something like this:

trait A[Out] {
    protected def foo(): Out
}

trait B extends A[Int]

class WrapperB(b: B) extends B {
    override protected def foo(): Int = b.foo() + 1
}

This won't compile, as WrapperB has no access to b.foo() .

There are a few ways to resolve this, but these won't work for me:

1. Make foo public: won't work, because I want it to stay protected .
2. Use a package scope: won't work, because I intend to have many B s in different packages.

Is there any other way?

Answer 1

How about:

trait A[Out] {
  protected def foo(): Out
}

trait B extends A[Int] {
  protected def gimme(that: B) = that.foo()
}

class WrapperB(b: B) extends B {
  override protected def foo(): Int = gimme(b) + 1
}

I have never liked the idea that private and protected can access other value's methods, I think it's bad design. private should mean private[this] . If you need cross-value access, I think you should declare private[my-package] , even if it means choosing a common base package in your case.