Private method inlining

Question

In the Scala immutable Vector code there is a comment that says:

In principle, most members should be private. However, access privileges must be car

Answer 1

I'm not an expert in "compiler decision" but logically I would say:

Let's imagine these two classes (in Java for instance):

class A {

  private B b;

  public void execute(){
    b.execute();
  }

}

class B {

  private int number;

  public void execute {
    println(number);
  }

}

If B's execute is inlined by the compiler into A's execute, it would lead to an illegal access since number is private in B:

class A {

  private B b;

  public void execute(){
    println(number);  //OUPS! number is unreachable directly from A
  }

}

So I would say that when you expect some "inlining", prefer to avoid some uncompatible variable's scope.

Of course, I would imagine it's useful in rare cases (mostly for performance optimization, I don't imagine other cases)..maybe the case you shew, otherwise it would lead to a lot of "bad encapsulations"...